National Documentation

Japanese Contribution to CLIVAR: Update

Japanese Committee for CLIVAR

March 2004

Preface

This documentation is an update of the former national report “Japanese Contribution for CLIVAR” submitted to International CLIVAR Conference in November 1998. Japanese research community has been actively participating in observational and modelling efforts in the whole area of CLIVAR-GOALS, DecCen and ACC. The present report describes the achievements relevant to CLIVAR so far and the currently on-going and planned activities which are expected to contribute to International CLIVAR Project. In this document, as in the former one, Japanese CLIVAR activities are described, for convenience, not according to the three streams of CLIVAR or the CLIVAR principal research areas, but to organizations/institutions and research projects. It should be noted that both the number of organizations/institutions participating in CLIVAR research and that of projects related to CLIVAR have been significantly increased since 1998, demonstrating growing contribution of the Japanese community to CLIVAR.

In Japan, there are also many individually-oriented research projects and small research projects, which are relevant to CLIVAR but can not be described in the text of this document in the format mentioned above. To include the information about the contribution from some of those projects, part of another national document, “Report of Oceanographic Studies in Japan for the period from 1999 to 2002” submitted to IAPSOXXIII General Assembly, is reproduced as an annex of this report.

Contributors for this document are as follows: Masaro Saiki (JMA) [Chapter 1], Hiroyuki Yoritaka (JCG) [Chapter 2], Tomowo Watanabe (FRA) [Chapter 3], Yoshihumi Kuroda (JAMSTEC) [Chapter 4], Yukio Masumoto (FRSGC) [Chapter 5], Kensuke Takeuchi (FORSGC) [Chapter 6], Hirohumi Sakuma (ESC) [Chapter 7], Ichiro Yasuda (Univ. Tokyo) [Chapter 8], Shiro Imawaki (RIAM/Kyushu Univ.) [Chapter 9], Masaaki Wakatsuchi (ILTS/Hokkaido Univ.) [Chapter 10], Nobuyuki Shikama (FORSGC) [Chapter 11], Masahumi Kamachi (MRI/JMA) and Toshiyuki Awaji (Kyoto Univ.) [Chapter 12], and Akimasa Sumi (CCSR/Univ. Tokyo) [Chapter 13]. March 2004

Toshio Suga Chairperson of Japanese Committee for CLIVAR

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< Contents > Page no. 1. Researches, Observations and Services Related to the CLIVAR 1

at the Japan Meteorological Agency (JMA) 1.1. GOALS 1.2. DecCen 1.3. ACC 1.4. Oceanographic observations, digitization of historical data, etc.

2. Observations Related to CLIVAR at Japan Coast Guard (JCG) 7

2.1. Tidal observation 2.2. Western boundary current 2.3. Repeat hydrography 2.4. Surface drifter

3. CLIVAR Related Activity at the Fisheries Research Agency 9

3.1. Oceanographic observation 3.2. Digitization of the historical data

4. JAMSTEC Research Activities Related to CLIVAR/GOALS 10

and DecCen 4.1. TRITON project and Tropical Ocean Climate Study 4.2. Global Ocean Circulation Studies 4.3. Arctic Ocean Research 4.4. Time-series observational study for biogeochemistry in the

northwestern North Pacific

5. Research Programs Relevant to CLIVAR/GOALS, DecCen, 18 and ACC at Frontier Research System for Global Change (FRSGC) 5.1. Frontier Research System for Global Change 5.2. Outline of research programs

6. Contribution of FORSGC to CLIVAR 27 7. Earth Simulator Project 28

7.1. Introduction 7.2. Contribution to CLIVAR as a unique computational center

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7.3. Collaborative high-resolution simulation researches relating to CLIVAR

7.4. Perspective on high-resolution simulation researches 8. SAGE (Subarctic Gyre Experiment) 32 9. Kuroshio Fluctuation Prediction Experiment 33 10. Study of the Sea of Okhotsk 40

10.1. Japan-Russia-United States joint project (1997-2002) 10.2. Amur-Okhotsk Project (2005-2010)

11. Argo Project in Japan 43

11.1. Introduction 11.2. Domestic organizations to conduct Argo and the objectives 11.3. Deployment of Argo floats 11.4. Technical issues 11.5. Distribution and quality control of Argo float data 11.6. Data analysis 11.7. Assimilation and prediction 11.8. International cooperation (1st Science Workshop)

12. Japan GODAE Activities 48

12.1. Background 12.2. Japan-GODAE Consortium 12.3. Data Product Serving

13. Model Development in Japan at the Era of the Earth Simulator 53

12.1. Introduction 12.2. Model development in Kyosei project 12.3. Other model development

Annex 1 Japanese Committee for CLIVAR 57 Annex 2 Recent Progress in Physical Oceanography in Japan 58

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1. Researches, Observations and Services Related to the CLIVAR

at the Japan Meteorological Agency (JMA)

CLIVAR related researches and operational observations and services between 1999 and 2003, and those planned in near future at the Japan Meteorological Agency (JMA) including the Meteorological Research Institute (MRI) are summarized briefly. Researches under the umbrella of GOALS, DecCen and ACC are described in Sections 1, 2 and 3, respectively. Oceanographic observations and those of atmospheric constituents are described in Section 4. 1. 1. GOALS 1.1.1. Operational ENSO Monitoring and Prediction

For ENSO monitoring and prediction, the JMA started the operation of a global ocean data assimilation system (ODAS) in 1995, and dynamical El Niño forecast with a coupled ocean-atmosphere model in 1998. Both the ODAS and the coupled model were upgraded in 2003. Major changes were replacement of an atmospheric component and introduction of an advanced ocean data assimilation system where salinity and sea surface height can be newly assimilated. Forecast skill of sea surface temperature (SST) is improved by this upgrade. Anomaly correlation coefficient of Nino.3 SST exceeds 0.7 and its RMSE remains below 0.7 degree Celsius even at six-month lead time. 1.1.2. Operational Seasonal Forecasts

The JMA began 3-month dynamical ensemble forecast operationally in March 2003 with the SST anomalies fixed to the initial values through the 4-month integration. In September 2003, the JMA started the 6-month dynamical ensemble forecasts targeting the cold season, December-January-February (DJF), and warm season, June-July-August (JJA). For the 6-month forecasts, the persistence of SST anomaly is not appropriate. In the JMA system, for the latter three months of the 7-month integration, the Niño3 (eastern-equatorial Pacific) SST anomalies are predicted with the El Niño prediction model (an atmosphere-ocean coupled model) first. Then, based on the MOS (model output statistics)-corrected Niño3 SST anomalies, global SST anomalies for the atmospheric model are obtained statistically with regression method. Considering that signal to noise ratio (S/N) in the extra-tropics is low and the model is imperfect at present, the model output is used mostly for the guidance to forecasters together with other statistical model results. 1.1.3. Operational Land Surface Data Assimilation)

In April 2003, snow data analyzed from SSM/I (Special Sensor Microwave Imager) has been applied to the land data assimilation system, which started its operation in April 2002

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using only the SYNOP snow-depth report. The output from the land surface data assimilation is used as the initial condition for the land model incorporated in the JMA seasonal forecast system. 1.1.4. Reanalysis Project

To respond to the serious requirements for the long-term reanalysis dataset for operational climate system monitoring and dynamical seasonal forecasting, the JMA started the Japanese 25-year Re-Analysis project (JRA-25) as a joint research project with the Central Research Institute of Electric Power Industry (CRIEPI) in April 2001. The project period is the fiscal years from 2001 to 2005. The target period is about 26 years from 1979 to 2004. The resolution of the model is spectral T106 (horizontal grid size around 110km) and 40 vertical layers with the model top level at 0.4hPa and the data assimilation scheme is 3DVAR, which was introduced in the JMA’s operational system in September 2001. At the end of the project, JRA-25 system will be inherited to the operational Japanese Climate Data Assimilation System (JCDAS). JRA-25 is the first re-analysis project in which historical position data of tropical cyclones (TC) and retrieved wind data around the TCs will be assimilated. TCs were analyzed correctly at the reported position with the retrieval data in a preliminary experiment. Production of JRA-25 will be started in March 2004.

1.1.5. CEOP

The JMA contributes to the Coordinated Enhanced Observing Period (CEOP) initiated on July 1, 2001 under the international coordination by providing the JRA-25 re-analysis data as well as Model Output Location Time Series (MOLTS) and gridded data of the NWP for the CEOP period from October 2002 to December 2004. The eventual purpose is to understand and improve the water and energy cycle processes of global models.

The JMA is involved in the Coordinated Enhanced Observation Period (CEOP) by providing model output data from the operational global data assimilation system. The data constitute the CEOP integrated data base and will serve for the Monsoon System Studies as well as the Water and Energy–cycle Simulation and Prediction. The JMA and the University of Tokyo cooperatively develop a satellite data assimilation technique for land surface variables such as soil water, soil temperature and snow. They also collaborate with each other in developing a land process model. The collaborations aim to elucidate the mechanism of the monsoon systems and to improve the operational forecasts ranging from daily to seasonal. 1.2. DecCen

The Pacific Decadal Oscillation (PDO) is known as the most prominent decadal to interdecadal variability in the North Pacific, and exhibits El Nino-like spatial pattern. Behavior and causes of the variability is continuously studied at MRI with coupled atmosphere-ocean GCMs (CGCMs), and connections with ENSO and the Arctic Oscillation (AO) are discussed. Another DecCen related variability of the Pacific is interdecadal modulation of ENSO, which is

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also studied at MRI with the CGCM to understand the mechanism. The AO index exhibits a large fluctuation in recent 30 years, which is a matter of concern associated with the global warming. With making a simulation for twentieth century climate change with the CGCM, studies on the different behaviors of the AO in response to external forcing and the internal climate variability is ongoing at MRI. 1.3. ACC 1.3.1. Operational activity at JMA

The JMA conducted a global warming experiment using a CGCM developed at the MRI with 1% per year increase of atmospheric CO2 and the effect of changes in sulphate aerosols. The results were published as “Global Warming Vol.3” in 1999. The JMA conducted a global warming experiment with a regional climate model developed at the MRI. Based on the experiment, a report on detailed climate change over Japan was published in 2001 as “Global Warming Vol.4”. The JMA conducted another experiment using a new version of CGCM developed at MRI using the SRES A2 and B2 scenarios. The results were reported in “Global Warming Vol.5” in 2003. Based on the A2 scenario experiment, using the regional climate model, a detailed climate change scenario over Japan has been computed and provided for the Climate Change Impact Study groups in Japan.

Global annual mean temperature is monitored based on the monthly mean temperature data (CLIMAT) reported from about 1200 stations over the globe. By averaging the temperatures at 17 stations with least effect of urbanization in Japan, the trend and long-term changes in annual mean temperature of Japan is monitored. 1.3.2. Research at MRI

The JMA is responsible for providing scientific information on the global warming to relevant organizations of the government. Projections of possible future climate changes due to the increase of greenhouse gases have been continued at the MRI with the use of CGCMs. Further improvements of oceanic part and cloud modeling are still marked with the highest priority among others to make the model projections without flux adjustments.

Studies using CGCMs have revealed that the global warming does not occur uniformly over the globe but has characteristic horizontal structure. Studies at the MRI showed that the characteristic horizontal structure found in the global warming has a close similarity to the one that occurs most dominantly as a part of natural variability of the climate system. In particular, the northern Pacific is affected by the Arctic Oscillation-like change combined with the ENSO-like change. Studies to clarify mechanisms behind the similarity will be continued further at the MRI with improved CGCMs.

Information about possible local climate changes in Japan due to the global warming is also very important for the planning of adaptation program to the global warming. The Baiu front and typhoon are very important phenomena which produce much rain in Japan in summer and

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fall. Any changes in them will have no little impact on the agriculture in Japan and the society. So far two kinds of experiments have been conducted toward that direction at the MRI: one with a localized high resolution model imbedded in a CGCM with an intermediate resolution, and the other with a very high resolution global atmospheric model forced by sea surface temperatures supplied by the CGCM. A high resolution RCM (Regional Climate Model) has been developed and a coupled atmosphere-ocean RCM is being developed for the former experiment. The latter experiment is now being conducted on the Earth Simulator. 1.3.3. Water resource and its variability in Asia in the 21st century

Japanese six institutes (MRI, NIES, NIAES, CSIS/UT, IIS/UT, CRIEPI) have participated in a project "Water Resource and Its Variability in Asia in the 21st Century (FY2001-FY2003)" that consists of (1) Spatial and temporal interpolation of land-use and land surface environment, (2) Projection of global and Asian water circulation, and (3) Future perspective of variability of water resources in Asia based on climate projection. In the first part, estimation of future land use has been done based on available future scenarios on population growth, urban expansion, industrial structure, agricultural productivity and possible changes in natural vegetation. Two global climate models (MRI and CCSR-NIES) are used under the SRES-A2 scenario, and three regional climate models (MRI, NIES and CRIEPI) are integrated for mid-21st century using boundary conditions obtained by two global climate models. Statistical downscaling method is also used! for Japan and China region. Finally, estimation of total future water demand is made based on estimation of population change, water demand due to agricultural use and better living standard and change in irrigation. This is contrasted with calculated future water resources, and assessment of water supply/demand balance is conducted. [A summary poster will be shown at the CLIVAR2004 Conference] 1. 4. Oceanographic observations, digitization of historical data, etc.

Quasi-periodical oceanographic observations by research vessels have been continued by the JMA. Oceanographic observations are made two or four times a year cooperatively by JMA’s five research vessels along the fixed lines, which are located to across the main ocean currents in the western North Pacific. Among them, oceanographic observation along 137E from south of Japan to the tropics has been continued over 36 years since 1967. Similar observations have been extended further along 165E from the sub-arctic region to the tropics since 1996 (see Fig. 1-1). These observations will be continuously maintained so that the data will be used to monitor oceanic variability of inter-annual to inter-decadal time-scale quantitatively in the western North Pacific.

CO2 exchange between atmosphere and ocean as well as total inorganic carbon inventory in the ocean has been measured as a part of regular observation in the quasi-periodical cruise stated above. The time series of monthly CO2 exchange in the subtropical area of the western North Pacific were estimated based on the empirical relationship between observed oceanic CO2 and sea surface temperature. The measurement so far clarified a very large

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seasonal change in the exchange and the role of ocean as a sink of CO2 in the western Pacific on the annual average basis. As the results of CO2 observation along 137°E in each winter since 1983, surface oceanic CO2 (partial pressure of CO2) was found to increase year by year. The increasing rate of oceanic CO2 was similar to that of atmospheric CO2, indicating that the increase of oceanic CO2 was attributed to the invasion of anthropogenic CO2 into ocean from atmosphere.

JMA had been operating three moored boys A, B and C located in the vicinity of Japan as shown in Fig. 1-1 until 2000. Instead of moored boys, JMA has been operating drifting ocean data buoys in the seas around Japan since 2000. These buoys automatically observe ocean waves as well as SST and air pressure. JMA has been participated in the Ship of opportunity Program, SOOP under the framework of JCOMM, to make XBT sampling by ships of opportunity. Collection and exchange of marine meteorological observations data by Voluntary Observing Ships (VOSs) have also been continued under the framework of JCOMM. Efforts will be made to continue these observations in future.

Fig. 1-1. A schematic picture to show oceanographic observations performed by JMA.

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A broad-scale global array of temperature/salinity profiling floats, known as Argo, is a major component of the global ocean observing system. In the Argo Project, JMA has taken part in the Argo data management system as Japanese national data center since the beginning of the project. It is currently processing 179 Japanese floats data, deployed by JAMSTEC/FORSGC, JMA, Meteorological Research Institute, National Polar Research Institute, Tohoku University and Tohoku National Fisheries Research Institute, as of 13th February 2004. All the profile data are issued to the GTS and the global data centers (GDACs) within 24 hours after observations in accordance with the Argo data management standard.

As one of the GOOS (the Global Ocean Observing System) Regional Alliances, North-East Asian Regional GOOS (NEAR-GOOS) has been implemented by People's Republic of China, Japan, Republic of Korea and Russian Federation since 1996. Exchange of ocean observational data in the North-East Asian marginal seas has been a first priority of NEAR-GOOS in its initial phase. JMA has been playing a leading role in planning and implementation of NEAR-GOOS particularly by operating the Regional Real Time Data Base, which collects all available real time ocean observational data and provides them to a wide range of data users.

Measurement of atmospheric constituents has also been conducted at the JMA. There are three Global Atmosphere Watch (GAW) monitoring stations (Minamitorishima, Ryori and Yonagunijima). Greenhouse gases and surface ozone concentrations are measured at these stations. Acid rain is monitored at Ryori and Minamitorishima. Besides them, ozone observations have been continued at five stations in Japan as well as at Syowa Station in Antarctica. Atmospheric turbidity is observed with Pyrheliometer at 14 meteorological stations and with Sunphotometers at the three GAW stations. In 2002, JMA newly installed a lidar at Ryori, and started the measurement of aerosol vertical profiles. These monitoring program will be continuously maintained by the JMA. In collaboration with the Japan Airline Foundation and the Ministry of Land, Infrastructure and Transport, the JMA has been monitoring concentrations of greenhouse gases at a height of 8 to 13 km twice a month by regularly scheduled airline flight between Australia and Japan since 1993.

The Kobe Collection is the historical marine meteorological data set observed by Japanese VOSs in the period from 1889 to 1960. About 2.7 million data of them observed in the period from 1933 to 1960 were digitized in 1960/1961 and had been included in the Comprehensive Ocean Analysis Data Set (COADS) Release 1. The project to digitize the remaining 3.14 million data of the collection observed in the period from 1889 to 1932 completed in 2003 with financial support of the Nippon Foundation. These data will contribute to research activities related to the climate change.

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2. Observations Related to CLIVAR at Japan Coast Guard (JCG)

2.1. Tidal observation

JCG maintains 30 tide gauge stations at the Japanese coast and Ongle Island of Antarctica. These stations supply long-term variation of sea level. Tidal observation at Antarctica was intermittently carried out from 1960’s and continuously conducted from 1980’s as a part of Japanese Antarctic Research Expedition (JARE) (Fig. 2-1).

2.2. Western boundary current JCG monitors the variation of the Kuroshio by vessels with ADCP, XBT/XCTD and tide

gauge stations at islands. Surface current monitoring of the Kuroshio by long range HF ocean radar was started from 2001 (Fig. 2-2).

Fig. 2-1. Sea level at Ongle Island of Antarctica.

Fig. 2-2. Surface current measured by long range HF ocean radar.

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1984 1986 1988 1990 1992 1994 1996 1998 2000

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5

10

15

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25

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13.514.014.515.015.516.016.517.017.518.018.519.019.520.020.521.021.522.022.523.023.524.0

Fig. 2-3. Year (horizontal axis) – Latitude (vertical axis) diagram of temperature averaged for upper

layer (0-300m) along 144°E.

Fig. 2-4. Tracks of surface drifters deployed by JCG.

2.3. Repeat hydrography JCG repeats deep hydrographic observation along 144°E line in the western North Pacific

(Fig. 2-3), along 110°E and 150°E lines in the Southern Ocean. Hydrographic observation including temperature, salinity, dissolved oxygen and nutrients are conducted every February along 144°E since 1984, every December along 110°E and every March along 150°E. Repeat hydrography in the Southern Ocean has been carried out as a part of JARE. 2.4. Surface drifter

JCG deployed surface drifters since 1978 in the Pacific Ocean, the Indian Ocean and the Southern Ocean (Fig. 2-4). These surface drifters were deployed as a part of various projects, such as WOCE/TOGA SVP, Kuroshio Exploitation and utilization Research (KER), Japanese Experiment on Asian Monsoon (JEXAM), Subarctic Gyre Experiment (SAGE) and JARE.

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3. CLIVAR Related Activities at the Fisheries Research Agency

1. Oceanographic observation

The Fisheries Research Agency (FRA) has several monitoring lines in the adjacent seas of Japan. The purpose of the monitoring is to investigate the structure and the variability of the marine ecosystem, which controls the fisheries resources.

In the Oyashio area, the FRA is maintaining the monitoring line called “A-line” off Hokkaido since 1987. Five to eight cruises are conducted every year. Various items from physical variables to chemical and biological variables are obtained at appropriate quality. The datasets are opened to the public. The Kuroshio ecosystem monitoring along the 138°E meridian line was launched in 1999 to investigate the marine ecosystem in the Kuroshio region south of the Honshu-island. The line is occupied every season. In 2002, the FRA also commenced the monitoring along the 31°45´N latitude line in the Japanese EEZ of East China Sea. Seasonal and inter-annual variation of the oceanographic conditions on the source region of the Tsushima Warm Current will be shown.

The FRA made plan of special research in the Kuroshio Extension and recirculation area in 2003/4 winter and 2004/5 winter by using the large research vessels of the Fisheries Agency as a part of Kuroshio ecosystem monitoring. The area is recognized as key area not only for the variation of the fisheries resources but also for the climate variation of the North Pacific. The results will be reported in the near future. 2. Digitization of the historical data

The FRA is undertaking the digitization of the historical oceanographic data that were observed by the fisheries research laboratories in Japan. The systematic oceanographic observation in the field of the fisheries research was started in 1918 and several thousand profiles were constantly obtained every year. It is expected that the available oceanographic data will drastically increase in the adjacent seas around Japan for the period before World War II. The data set will be opened via internet to the research community.

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4. JAMSTEC Research Activities Related to CLIVAR/GOALS and DecCen

The Japan Marine Science and Technology Center (JAMSTEC) will be abolished by the end

of March 2004, and restarted as Independent Administrative Institution, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) in April 2004. The following activities shall be continued by the new organization. 4.1. TRITON project and Tropical Ocean Climate Study

The Japan Marine Science and Technology Center (JAMSTEC) began the surface mooring project with feasibility studies, conceptual buoy design, and simulation of buoy motion during 1992-1994. The prototype buoy was built in 1995, and since 1995, the open sea tests were carried out. The project was named as TRITON (TRIangle Trans-Ocean buoy Network), where the TRIANGLE means three themes and geographical regions of (1) ENSO in the tropical Pacific Ocean, (2) Asian monsoon in the western Pacific and Indian Oceans, and (3) decadal variations in the northern Pacific Ocean.

The array in the western tropical Pacific Ocean aims to monitor ENSO jointly with TAO array, and furthermore to elucidate the generation and dissipation mechanism of the warm pool emphasis on salinity changes. The deployment of TRITON buoys started in 1998 at four sites along 156°E in the western tropical Pacific Ocean (Fig. 4-1). TAO buoys west of 156°E were replaced with TRITON buoys, and the TAO/TRITON array officially began in January 2000. Two TRITON buoys were deployed in the eastern tropical Indian Ocean in October 2001. One TRITON buoy is located at 1.5°S, 90°E to determine the upper-layer variations associated with the zonal jets along the equator (originally it was planned at 0°, 90°E, but technologically it is difficult to design the buoy under the Indian Ocean equatorial jets). The other buoy is deployed at 5°S, 95°E, to investigate the contribution of the surface heat flux and the ocean dynamics/thermodynamics to the SST variability in the eastern part of the Dipole Mode. This location corresponds to the center of the area where the maximum SST anomaly appears during the peak period of the Dipole Mode. In August 2002, originally planned TRITON array consisted of eighteen buoy sites was completed. In JFY 2004, 17 TRITON buoys will be operated, and will be continually operated in next five years as same as present buoy numbers.

All TRITON buoys take the standard set of measurements sampled on the TAO array. Additionally, they all sample for salinity down to 750 m depth and include current at 10 m depth. Standard recording of measurements is done every 10 min, while real-time data consist of hourly means of these 10-minute records. Because of the vandalism, the moorings along 130°E and 0°, 138°E have no meteorological instruments. The data from TRITON buoys and detailed information on the project can be obtained from TRITON home page (http://www.jamstec.go.jp/jamstec/TRITON/).

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Fig. 4-1. Development of the TRITON array.

Fig. 4-2. TOCS subsurface ADCP mooring array.

JAMSTEC launched a research program named the Tropical Ocean Climate Study (TOCS) in 1993 as its own project. The purpose of the TOCS program is to observe physical oceanic conditions in the western tropical Pacific for better understanding of ocean-atmosphere interaction with emphasis on ENSO phenomena. The TOCS program has been successfully continued since 1993. Subsurface ADCP moorings have been deployed to measure the equatorial currents and low latitude western boundary currents as the New Guinea Coastal Current and Mindanao Current (Fig. 4-2). As part of the TOCS program, the TRITON project is supported by the Ministry of Education, Culture, Sports, Science and Technology.

March, 1998 March, 1999 March, 2000

March, 2001 March, 2002 August, 2002

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4.2. Global Ocean Circulation Studies The ocean is a major factor in determining the global climate and its variability. However,

to date there has been no empirical quantification of the volume of heat and material (e.g. nutrients) transports, their regional convergence, and temporal changes. This means that we have no firm grasp of the real state of global warming, and also that the empirical data for any climate model relating to heat and material transports are inadequate. This research is aimed to clarify the distribution of stored heat and dissolved material on the basin scale and their transports through surface and deep current system by implementing intercontinental high-precision observation (revisits of WOCE-WHP lines), and to understand the ocean's role in the global climate system. We also aim to clarify decadal changes in heat and material contents of the ocean by comparing up-dated observation results with foregoing results (Fig. 4-3). The deep-water exchange which will be determined through deep moorings between ocean basins will be a great help for understanding of possible changes in the global thermohaline circulation.

During the 1990's basin-scale hydrographic observations were carried out along as many as 80 observation lines throughout the world's ocean with the highest accuracy at the time. Eleven of those observation lines were located in the North Pacific Ocean. These accurate observation lines will be observed again by 2009 internationally to provide answers on long-term oceanic changes, e.g. how is global warming impacting on the ocean, and at the same time, to provide data for climate models and for various other usages.

Taking the lead in this, Japan conducted accurate observation on two lines in the North Pacific Ocean. A zonal observation in the Pacific Ocean was carried out in 1999 as a collaborated program by the Fishery Agency, Tokai University, JAMSTEC, Agency of Industrial Science and Technology and the Canadian Institute of Ocean Sciences, all of which took part in the “International Research on Subpolar Circulation and Climate Change” project. JAMSTEC’s R/V Mirai also participated in the observation. In 2001, researchers from JAMSTEC and the Fishery Agency boarded R/V Mirai and carried out another revisit of a line extending diagonally across the Gulf of Alaska.

In 2003, Pacific Ocean observation has started with the southern hemisphere observation mission (BEAGLE 2003). This is expected to make an important contribution to understanding of the ocean climate change through the collection of data that can be compared with the results of high-precision observations in the 1990s.

As a local intensive observation, five deep mooring sites measuring water temperature, salinity, and current direction and speed have been started in the Wake Island passage which is the only corridor where the North Pacific bottom water is supplied from the South Pacific Ocean.

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Fig. 4-3. Research purpose and area of the global ocean circulation studies. 4.3. Arctic Ocean Research 4.3.1. JWACS2002 joint field experiment

Historically, the Arctic Ocean was assumed to exhibit little spatial and temporal variability and to have little impact on climate and the global heat balance. This highly inaccurate view has been corrected during the past decade. For example, the climatological summer ice edge was located on the shelf breaks along the perimeter of the Canada Basin in the Western Arctic Ocean. However the edge has now moved into the Canada Basin greater than 74N north of the Bering Strait after 1997 except 2001. The geographical distribution of recent ice reduction suggests the influence of Pacific inflow on the Western Arctic climate system. The global climate system is established by a balance between heating in the low latitude and cooling in the polar regions. The Arctic change could cause a change in the balance of the current climate state. Under these backgrounds, JAMSTEC and Fishery and Oceans of Canada (DFO) agreed to initiate joint observation oriented project called JWACS (Joint Western Arctic Climate Studies). The overarching goal is to prepare for global change and to reduce uncertainties in forecasting, a substantial improvement in our fundamental understanding of processes controlling variability in Arctic climate systems, specifically, of shelf/basin interactions, and inter-basin forcing of ice and water properties of land/ocean exchanges.

JWACS 2002 filed experiment (Fig. 4-4) is coordinated by multi ship operation using R/V Mirai, CCGS Louis S. St-Laurent and CCGS Sir Wilfrid Laurier to cover the entire southern Canadian Basin, to establish the climate mooring stations in the Canada Basin. R/V Mirai (MR02K05 leg1) was in charge of multi-disciplinary studies mainly focusing on the shelf-basin interaction.

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Fig. 4-4. JWACS hydrographic stations occupied by three vessels, R/V Mirai, CCGS Louis S.

St-Laurent and CCGS Sir Wilfrid Laurier. US station is also described in the map.

The research missions of R/V Mirai are summarized as: (1) Basin scale ocean circulation Conduct a CTD/XCTD, water sampling survey in the full span of the Southern Canada Basin from off Mackenzie shelf into the Chukchi Abyssal Plain west of the Chukchi Borderland. Hydrographic revisit of SHEBA 97 section from North Slope to near the initial SHEBA site. Hydrographic revisit of SHEBA 97-98 drift section. (2) Shelf basin interaction processes Conduct a CTD sections across/along the shelf breaks and submarine canyons. Conduct an underway ADCP and surface water sampling. (3) Plankton sampling (4) Carbonate chemistry Observation of partial pressure of CO2 (pCO2), total alkalinity, total dissolved inorganic carbon (TDIC), dissolved oxygen and nutrients in order to assess the spatial and temporal variations of budget and flux of CO2. (5) Atmospheric science Radiosonde, Tethered balloon, Doppler radar, and Aerosol observations are conducted. (6) Paleo Oceanography and geology Piston samplings at three locations in the Mackenzie Canyon were conducted. Surface sediment core samplings were conducted over the Kopanor Mud-volcano in the Mackenzie shelf. Underway surveys using Seabeam and Sub-bottom profiler surveys were conducted. High resolution survey of sea floor topography was conducted in the vicinity of the mud volcano.

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Fig. 4-5. Drift trajectories of J-CAD after 2000.

4.3.2. JWACS 2003

In the Arctic Ocean, there are data missing area still remains. The missing areas in the western Arctic Ocean are the Eastern Canadian Basin and Makarov Basin. We have carried out JWACS in the areas using heavy ice breaker CCGS Louis S. St-Laurent. 4.3.3. Long term monitoring of the Arctic Ocean

We have initiated a long-term observatory at the North Pole and in the Eastern Arctic Basins with US team since 2000 (Fig. 4-5). Our automated drifting buoy called J-CAD has been installed at North Pole since 2000 as a main platform of the NPEO (North Pole Environmental Observatory). We are scheduled to deploy at least one J-CAD until 2004 at North Pole. 4.4. Time-series observational study for biogeochemistry in the northwestern North Pacific

Mutsu Institute for Oceanography of JAMSTEC initiated new decadal time-series observation program with using advanced mooring system in 2001. This program called HiLaTS (High Latitude Time-Series observatory) is a joint program with JPAC group of Woods Hole Oceanographic Institution (HilaTS web site: http://jpac.whoi.edu/hilats). We decided three time-series stations in the northwestern North Pacific. Each stations called K1 (51°N, 165°E), K2 (47°N, 160°E), K3 (39°N, 160°E) are located in the north boundary and center of the Western Subarctic Gyre, and the boundary of the subtropical gyre, respectively (Fig. 4-6).

16

As Sea WiFS chl-a map shows, these stations are expected to have different biogeochemical and physical oceanography.

The BGC mooring system consist of, not only ordinary sediment trap in the deep sea, but also subsurface Incubation Chamber for measurement of primary productivity (SID), automatic water sampler (RAS), phyto and zooplankton sampler installed in the surface euphotic layer (Fig. 4-7). Optical sensors such as fluorometer and radiometer are also mounted on the SID flame. Moreover, in order to study material cycle in the twilight zone, 10 sediment traps were tied in a row on BGC mooring system at station K2. On the other hand, in order to know physical oceanographic circumstance, we also deploy shuttle CTD with acoustic current meter, called MMP around mooring for Biogeochemistry.

We deployed the above mooring systems at stations K1 and K2 in September, 2001, and recovered these mooring systems successfully in October, 2002. Various time-series samples and data were obtained and the preliminary results demonstrate interesting seasonal change. Surface water samples obtained by using automated water sampler (RAS) deployed at approximately 50m show seasonal variability in nutrients. Nutrients’ concentrations varied largely in autumn. It is likely that winter mixing starts in this period and surface water with low nutrients and intermediate water with high nutrients invades to 50 m depth extemporaneously. This is supported by shuttle CTD (MMP) data. Concentrations increased toward winter and maximum concentration was observed in March. From April, concentrations decreased toward summer. It is attributed to the fact that biological activity consumes nutrients in the upper water.

Thus, the automated instruments enable us to conduct time-series observation for biogeochemistry in the North Pacific where it is very tough, especially in winter, to do so by using ordinary research vessel. This study will be continued using JAMSTEC research vessels to visit and maintain the HiLaTS moorings.

Fig. 4-6. Mooring sites of the time-series observational study for biogeochemistry in the northwestern

North Pacific.

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Fig. 4-7. Mooring systems used in the time-series observational study for biogeochemistry in the northwestern North Pacific.

　-

BGC

~ 30m

~ 40m

~ 50m

~ 1000m

~ 2000m

~ 5000m

5100 ~ 5200m

PO

~ 30m

~ 50m

~ 4550m

Water sampler

Phytoplankton sampler

Incubation Device

Zooplankton sampler

Sediment Trap

Shuttle CTD / ACM (MMP)

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5. Research programs relevant to CLIVAR/GOALS, DecCen, and ACC

at Frontier Research System for Global Change (FRSGC) 5.1. Frontier Research System for Global Change (FRSGC)

Frontier Research System for Global Change (FRSGC) was established in 1997 as a joint program between National Space Development Agency of Japan (NASDA) and Japan Marine Science and Technology Center (JAMSTEC) to promote mainly process studies for climate simulations. FRSGC consists of six research programs based in Japan and two international research centers at Hawaii (International Pacific Research Center; IPRC) and Alaska (International Arctic Research Center; IARC) (Fig. 5-1), focusing on climate variability, hydrological cycle, global warming, atmospheric composition, biological processes and model integrating studies. IPRC and IARC were established under Common Agenda for Global Perspectives between the US and Japanese governments. Since JAMSTEC will change to a new organization in April 2004, the following research plans are subject to changes accordingly. All the research activity in FRSGC, however, will contribute more or less for CLIVAR/GOALS, DecCen, and ACC in many ways.

5.2. Outline of research programs 5.2.1. Climate Variations Research Program (Research on climate change prediction in the Asia-Pacific region) (1) Scientific objectives

The objectives of this research program are to elucidate the climate change and related phenomena occurring in the atmosphere and ocean particularly in the Asia-Pacific region (including the Indian Ocean and polar and subpolar ocean regions) and to contribute to constructing a sophisticated system to predict these phenomena. It is principally aimed at getting deep understanding of the underlying processes chiefly by means of experimentation and data analysis using an atmosphere-ocean model with various degrees of freedom. This research program will concentrate on model research by using models with very high degrees of freedom; however, a theoretical study will also be promoted using a mechanical system model with relatively low degrees of freedom to deepen the understanding of predictability. (2) Research subjects a) Analysis of short-term climate variations including seasonal variations and elucidation of their occurrence mechanisms

The study comprehends short-term climate variations such as El Niño/Southern Oscillation (ENSO), Indian Ocean dipole (IOD) events, the quasi-biennial oscillation in the troposphere, remarkable seasonal variations typified by monsoon. The study also extends to the researches on atmospheric variations including Aleutian lows, and ocean current variations in the Pacific and Indian Oceans such as the Kuroshio Current, Indonesian Throughflow, and Wyrtki-Yoshida

19

Jets, and aims at elucidating and predicting their occurrence mechanisms. Efforts will be made to elucidate the interactions between these various phenomena.

Fig. 5-1. Structure of Frontier Research System for Global Change (FRSGC).

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b) Analysis of climate variations on decadal and interdecadal time scales and elucidation of their occurrence mechanisms

The study will analyze atmospheric and oceanic phenomena lasting one to several decades such as the regime shift of the North Pacific climate in 1976, Antarctic circumpolar wave, and variations of meridional circulation in the Pacific and Indian Oceans and contribute to the elucidation of their occurrence mechanisms. Efforts will be made to elucidate their interrelations with other phenomena of different temporal and spatial scales such as oceanic subduction process, storm tracks, and anomalies of intraseasonal variations. 5.2.2. Hydrological Cycle Research Program (Research on hydrological cycle prediction in the Asian region) (1) Scientific objectives

The water resource of Asian countries depends largely on the precipitation by monsoon in the summer and winter. Meanwhile, since the hydrological cycle on the continental scale are fed back to the variations of the monsoon climate through energy transfer processes, understanding the physical processes is also important for mechanism elucidation of hydrologic cycle variations. In particular, the way in which hydrologic cycle processes in a continental region affect the ENSO and monsoon system in the Asia-Pacific region is an important research subject to understand and predict variations of the Asian monsoon and global climate system. In addition, studying effects of the increase in greenhouse gases on climate and hydrological cycle variations in Asia is an urgent issue to be considered in this region. In order to predict seasonal and inter-annual changes of precipitation and hydrological cycle variations in the Asian and Eurasian Continent, this research program will conduct the process elucidation of the each hydrological cycle in a large-scale atmospheric and hydrospheric system, modeling of cycles (based on the process elucidation), and development of datasets needed for these studies. (2) Research subjects a) Elucidation of wide-area hydrologic cycle processes

Using the global objective reanalysis data and Global Circulation Model (GCM), this study focuses on seasonal and interannual variations of energy transfer and hydrologic cycle processes in the Asian monsoon region and the ENSO-monsoon system. In particular, this study will attempt to describe these processes in relation to the interaction between cloud and precipitation, land surface and biosphere, and among the atmosphere, land and ocean. In addition, the study will elucidate not only the Eurasian hydrologic cycle and transportation, but also the Lagrangian hydrological cycle process to investigate the water vapor source and water re-circulation process, using the hydrogen and oxygen isotopes as tracers. b) Elucidation of land surface water circulation processes

This research program extensively studies the detailed process analysis and conducting the modeling of the energy and water cycles in following areas; 1) the process in cold regions underlain by permafrost and 2) the process in the biosphere, such as taiga, tropical rain forests,

21

and tropical monsoon forests. With continental-scale river basins as subjects of investigation, the group will clarify and conduct the modeling of one-dimensional and tow-dimensional processes of precipitation, evaporation, and outflow. c) Elucidation of cloud and precipitation processes

The research group will develop and establish a new meso-scale cloud-resolving model and a cloud-scale numerical model of micro-physical processes, based on synthetic observations by artificial satellites, aircraft, research vessels, meteorological radar. This research group mainly focuses on 1) hydrological cycle variations in the sub-tropical frontal zone, and the role of meso-scale could system, 2) elucidation of the precipitation process and prediction method using the cloud-resolving meso-scale atmospheric model, and 3) development of cloud-scale micro-physical model, and the effect of aerosol on the cloud process. 5.2.3. Global Warming Research Program (Research on the forecast of climate changes related to the global warming) (1) Scientific objectives

The main goals of this research program are: to elucidate physical, chemical and biological processes which control global warming and to contribute to the reliable estimation of global warming. This program consists of three research groups. The global warming research group aims to understand the climate change induced by increase in carbon dioxide concentration in the air and attempt to project the change using a climate model. The goal of the carbon cycle research group is to understand the mechanism of global carbon cycle and to simulate the change of CO2 concentration in the atmosphere. The paleoclimate research group explores the dynamical and chemical processes that controlled climate changes of the geological past. This group also attempts to evaluate and validate the sensitivity of model climate through paleoclimate simulation. (2) Research subject a) Global Warming Research Group

Using the existing climate models as the base, the group will develop a high-resolution climate model and conduct various sensitivity tests related to physical process improvement in order to improve the accuracy and reliability of global warming predictions. To study the effect of global warming on climate variation of interannual, decadal and/or multi-decadal time scales, long-term integration (1500 to 2000 years) of coupled ocean-atmosphere models is performed for various concentrations of greenhouse gases. In addition, the influence of global warming on atmospheric disturbance such as tropical cyclones and Baiu front and heavy, convective precipitation are examined. Particularly, the influences of geography and land surface conditions upon regional/local climate are studied in detail.

b) Carbon Cycle Research Group

To accomplish the quantitative prediction of carbon dioxide concentration in the atmosphere,

22

the following three subjects are established. ･The oceanic carbon dioxide absorption and concentration distribution in the oceans in the

case where anthropogenic carbon dioxide is added in a perturbative manner. ･How the equilibrium condition of natural carbon dioxide changes if a virtual change is given

to the ocean circulation and life activities. ･Concrete cases of large variations of the ocean circulation and life activities such as global

warming and the last glacial age and assess their influence on the material cycle. c) Paleoclimate Research Group

General circulation models are used to simulate the paleoclimate and its variations to elucidate its physical and chemical mechanisms. The study is divided into three subjects as follows: ･By reproducing past atmosphere and ocean conditions which greatly differ from the present,

the climate sensitivity of the models is assessed, to examine in what conditions the atmosphere, ocean, ice sheet and other subsystems were maintained for each period under the given earth orbital elements and carbon dioxide content in a snap-shot manner.

･The study examines how the large ice sheet on the Antarctic continent and in the northern hemisphere respond to atmospheric and ocean variations to understand the maintenance and variability of the ice sheets.

･The study assesses astronomical theories which can explain the large climate change in the Quaternary period.

5.2.4. Atmospheric Composition Research Program (Research on atmospheric composition variations in the Asia-Pacific region) (1) Scientific objectives

The objective of this research program is to elucidate the physical and chemical processes of transport, transformation and deposition of atmospheric trace constituents related to climate change or atmospheric pollution with the Asia-Pacific region (including the central Eurasian Continent and Arctic regions). The research group will draw a chemical weather map of this region and construct a model to forecast future atmospheric composition variations including the feedback of the climate change in order to achieve advanced future forecasts. To attain this objective, this research program will elucidate the processes underlying the atmospheric composition change by constructing atmospheric chemical models such as a regional-scale chemical transport model, 3-dimensional global chemical transport model, and coupled atmospheric general circulation-chemical model and by acquiring and analyzing observation datasets and constructing a database. (2) Research subjects a) Transport and chemical transformation processes in the East Asia-West Pacific region

To quantify the ozone budget in East Asia, including Northeast and Southeast Asia, and make a forecast of its long-term trend, the study tries to quantify the atmospheric boundary

23

layer-free troposphere material exchange process of ozone precursors and ozone itself and the photochemical ozone formation and extinction processes involved in the long-distance transport. For quantification of ozone budget in tropical or low-latitude Southeast Asia, this study also elucidates the tropospheric vertical mixing process and acquires observation data of precursor concentrations in the dry and wet seasons for model analysis based on the acquired data.

In order to assess the radiation and environmental impact of aerosol in East Asia and East Pacific regions including tropical or low-latitude Southeast Asia, the study acquires observation data for model building and verification for long distance transport of its physical/chemical processes and the atmospheric boundary layer-free tropospheric diffusion process. b) Intercontinental long-distance transportation mechanism

This study analyzes the trans-Eurasian long-distance transport and the transport to the Arctic region of the European outflow using a global model in order to assess its impact on East Asia and provide a guideline for future atmospheric constituent observation in Central Asia. c) Variations and circulation of greenhouse gases

This research aims to elucidate the mechanism for global variations and circulation by collecting observation data related to the time and space variations in isotopic composition of the greenhouse gases observed in a wide area using ground observatories, aircraft and vessels and analyzing these data using a 3-dimensional global model. 5.2.5. Ecosystem Change Research Program (Research on prediction of ecosystem changes in the Asia-Pacific region) (1) Scientific objectives

This program aims to clarify the structure and functions of ecosystems in relation to global climate and environmental changes, as well as to develop models of those. In particular, it tries to understand the mechanisms how climate and/or environmental changes affect ecosystems, and vice versa. For the terrestrial ecosystem, focusing on Asia-Pacific regions, parameters such as distribution of vegetation, biomass and primary production in various climate zones will be modeled, and models of the ecosystem changes along with material cycles and interactions between ecosystems and atmosphere are developed. For ocean ecosystems, changes in structure and functions of biota at the ocean surface, which play important role in ocean material cycles, over years to decades’ period, and physical environment at the ocean surface layers are integrated into the models based on elaborate analysis of current data on the ocean and data from satellites. (2) Research subjects a) Study on ecosystem-atmospheric interaction system

Coupled ecosystem-atmospheric models will be established in order to predict how ecosystems respond to the terrestrial ecosystem changes and environmental changes. The high-resolution models for the terrestrial ecosystem changes with biological information would

24

be developed based on CO2, H2O and heat balance. In particular, the study focuses on; ･Global terrestrial material cycles and ecosystem model ･Atmospheric-terrestrial interaction models

b) Study on the ecosystem architecture change

The Dynamic Global Vegetation Model (DGVM), which can forecast long-term (100 years’ scale) changes of the terrestrial ecosystem’s feedback to climate and environment changes, is aimed to be developed in this component. Since this component combines different spatial scales, the model development is carrying out along with two sub-components; the foliage module model and the forest change model. c) Study on the ecosystem geographical distribution change

This component will evaluate spatial distribution of ecosystem parameters (i.e. vegetation, soil, etc.), thence analyze relationship between changes in their spatial distribution and environmental factors such as temperature or rainfalls. The most challenging subject in this component is to observe conditions of land surface coverage in East Asia by remote sensing from satellites. d) Study on marine biological process changes

It is aimed to develop models of changes of structure and function of biota at the ocean surface layers (phytoplankton, zooplankton and commercial fish), which play the significant role within ocean ecosystems in the process of the material cycle. Relationship between ocean ecosystems changes with scales of years to decades and changes in ocean surface environment is to be elucidated by analyzing historical data and latest data obtained through ongoing various international projects. 5.2.6. Integrated Model Research Program (1) Scientific objectives

The objective of this study is to develop a climate model, which combines the atmosphere, oceans and land surface processes by utilizing the results of other research programs on the individual processes. The researchers are making the most advanced climate model (horizontal resolution about 10 km) of the time to run on the Earth Simulator. (2) Research subjects

The group studies dynamical frame that suits the order of horizontal resolution of 10 km and develops a new scheme appropriate for incorporating with global model based on the detailed knowledge on individual processes such as radiation, cloud, and land water processes. Then this scheme will be combined with the existing model and the effect will be examined by the sensitivity experiment. The group also analyzes the mechanism for global individual phenomena (for example, intraseasonal oscillation of tropical atmosphere and subduction of Antarctic peripheral seas) using existing models and through numerical experiments.

25

5.2.7. FRSGC’s program for the International Pacific Research Center (IPRC activities funded by Japan) (1) Scientific objectives

The International Pacific Research Center (IPRC) was established with the cooperation of Japan and the United States to deepen the understanding of signals indicating global environmental changes occurring in the Asia-Pacific region and contribute to the scientific studies for prediction of such changes. As a whole, research on:

1) prediction of climate changes in Asia and Pacific 2) prediction of hydrologic cycle 3) relationship of the global warming phenomenon with regional climate changes

is promoted mainly through data analysis and model experiments. Japan is planning to give priority to the research of 1) for the time being though giving consideration to 2) and 3). (2) Research subjects a) Research on atmosphere-ocean processes connecting Asian monsoon and ENSO

The subject is to elucidate atmosphere-ocean processes which connect the monsoon and ENSO, including, among others, the relation of the intraseasonal to decadal east-west shift of a tropical tropospheric heating zone with the Asian monsoon, the relation of tropical seawater temperature with the meridional circulation of the oceans and with the Hadley circulation of the atmosphere, and the role of the interactions of low- and mid-latitude ocean circulations for heat and fresh water transportation. b) Elucidation of atmospheric and oceanic processes causing long-term variations of North Pacific climate system

The study will elucidate the decadal and multidecadal variations of the North Pacific climate system, clarify the variation mechanisms, and conduct research on their predictability. In particular, the research will elucidates the relationship between short-term climate changes and long term anomalies in the tropical regions. c) Elucidation of the role the Asian and Indian marginal seas and Indonesian Archipelagos have in the Asia-Pacific climate system

This subject is also to elucidate 1) the role of active tidal mixing on surface layer temperature, 2) the relationship of variations of ocean currents such as the Oyashio, Kuroshio, Mindanao currents and Yoshida-Wyrtki Jet with variations in the marginal seas, and 3) the role the Indonesian Throughflow has in the heat and freshwater transportation between the Pacific and Indian oceans. 5.2.8. FRSGC’s program for the International Arctic Research Center (IARC activities funded by Japan) (1) Scientific objectives

The objectives are to elucidate the role of the Arctic region in global climate change as well as to predict the impact that will noticeably appear in the Arctic region in process of global

26

warming or other global change taking place. The possibility of feedback to global climate change will also be elucidated. To accomplish these major objectives, it is essential to understand the physicochemical behavior of a coupled system of ocean, sea ice and atmosphere. To predict the response of marine and land ecosystem to climate change as well as the possibility of the ecosystem to affect the climate change is another objective. (2) Research subjects and methods of study a) Coupled ocean-sea ice-atmosphere system a-1. Ocean-sea ice system

Our efforts so far have accomplished the construction of a coupled sea ice-ocean system. To make a prediction more reliable, several key physical processes must be parameterized. Formation and diffusion of high-density water, and sea ice dynamics and thermodynamics are particularly important processes, and we will conduct the intensive research on these to obtain initial results. The results of parameterization will be integrated to a coupled sea ice-ocean model to contribute to construction of a reliable Arctic Ocean model. a-2. Atmosphere-radiation equilibrium

To describe climate change having various time scales, the study collects and analyzes manifold data obtained by various means such as daily weather observation, ocean vessel observation, and remote sensing from satellites. Concurrently with the verification of a radiation model, we will construct a coupled model comprising atmosphere dynamics model and sea ice model for comparison with those data. a-3. Coupled atmosphere-ocean model

To elucidate the complex Arctic climate system, the study describes the phenomena through data gathering and analysis, interpret them using a logical model, and predict them with a numerical model. After the examination of atmosphere models and coupled sea ice-ocean models, we will construct a coupled atmosphere-ocean model. By accumulating analysis results of ice sheet and seabed core, the climate change in the past 100 thousand years will be described. b) Biochemical process and ecosystem

Field observation is conducted for elucidation of bio-geochemical processes in the arctic regions. Under severe natural conditions, remote sensing data from satellite is also utilized for the analyses. At the present stage, research in this study focuses on phenomena which affect the atmosphere-ocean system with such phenomena integrated into the atmosphere-ocean model.

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6. Contribution of FORSCG to CLIVAR

Frontier Observational Research System for Global Change (FORSCG) started in 1999, as a project sponsored by JAMSTEC. It is consists of 3 programs, Climate Variations Observational Research Program, Hydrological Cycle Observational Research Program and Observational Research at the International Arctic Research Center. All the three programs are contributing to CLIVAR to some extent, but for Hydrological Cycle and IARC programs, their main contributions are to GEWEX and ACSYS, respectively. The Climate Variation program is the main contributor to CLIVAR.

For the Climate Variation program, three groups are carrying out the three sub-programs Kuroshio, Argo and Tropics, respectively. The Kuroshio group has been observing ocean currents around Ryukyu Archipelago. The Main stream of Kuroshio is on the East China Sea side of the archipelago, but theories and models had been suggesting the deeper port of Kuroshio should be flowing on the Pacific side of the archipelago. By the observation, they found a northeastward current with subsurface core on the Pacific side of the archipelago.

The Argo group is the main group carrying out Argo Project in Japan. The group is working with a group in the Observational Research Division of the same JAMSTC, and is in charge of float deployment and delayed mode data management. The group deployed almost all the Japanese Argo floats, in total 243 floats in the past 5 years, mainly in the Western North Pacific, but also some in the Southern Pacific, Indian Ocean and Southern Ocean. The Japanese contribution to the international Argo project is the second in the world in number of floats, only next to US.

The Tropics group is consists of two sub-groups. One group is observing convective activities in the warm water pool region in the Western Tropical Pacific. They set the station in Palau for continuous observation, and in intensive observation periods, R/V Mirai or aircrafts are also used for observation in the warm water pool region. The other group is observing ocean variations in Indian Ocean. They are keeping an ADCP mooring at the equator in the Eastern Indian Ocean. They found strong influence of intra-seasonal oscillation and their year-to-year variation, in the current in the upper layer. They are also carrying out VOS XBT and XCTD observations in the Western Tropical Pacific and Indian Ocean.

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7. Earth Simulator Project 7.1. Introduction

The Earth Simulator (ES) initiated its operation from the spring of the year 2002 shortly after attaining the expected theoretical peak performance of 40 Tflops and soon it was ranked number one in the world by achieving 35.86 Tflops in Linpack Benchmark, which outperformed the second-ranked ASCI White by approximately five times. Since then variety of code performance tests have been done and, among others, it was quite noteworthy that a state-of-the-art AGCM code optimized by Earth Simulator Center (ESC) also attained record-braking performance of 26.58 Tflops (66% of the peak performance) and our OGCM code successfully accomplished a 50 years-long eddy-resolving spin-up experiment, which was an untrodden realm of time integration for the global domain.

We believe that a couple of those successful accomplishments mentioned above, though quite preliminary from the view point of CLIVAR’s research goals, are surely considered as important milestones for the future high-resolution climate simulation studies. Presumably, the biggest contribution of ES to climate simulation research community in general would be the remarkable stability of our hardware system with which we can host not only domestic but also foreign research institutes either by formal research collaborations or by participating in the research consortiums we organize. And now, the number of simulation research activities is steadily increasing and in what follows we will give an overview of our center’s activities done so far, which could be relevant to CLIVAR’s research goals in a loose sense.

December/2003The Earth Simulator Center 63

Allocation of Computer Resources

20-30%

10%

30-35%

15-20%15%

Ocean and Atmosphere

Solid EarthComputerScience

Epoch-making Simulation

Director General's Discretion

# of p roject # of p roject in 2002 in 2003

Ocean and Atmosphere 17 12Solid Earth 8 9Computer Science 4 2Epoch-Making Simulation 11 11

Research fieldsSelected Projects

Fig. 7-1. Allocation of CPU time.

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7.2. Contribution to CLIVAR as a unique computational center ESC is a unique computational center where we encourage high-resolution simulations.

Although ES is a mainframe for general purposes, reflecting governmental priority, as we see in Fig. 7-1, the maximum CPU time is allocated to the field of ocean and atmosphere simulation researches, in which a few government-funded projects as a part of the bigger national project called Research Revolution 2002 (RR2002) occupy as major uses in these fields. They are the studies on the global warming, hydrological cycle as an important and specific extension of more general climate researches and on the data assimilation as a necessary research infrastructure for climate modeling. The first study is directly linked to CLIVAR-ACC and the remaining two are relating either to CLIVAR-GOALS or CLIVAR-DecCen. These three are expected to be major contributors to CLIVAR as unique simulation researches accomplished only with the use of ES. More detailed description of these three projects is given mainly in the Chapter 13 and partly in Chapters 5 and 12.

In addition to these activities, ESC has been developing foreign collaborations among which climate-related fields are major components of the collaborative activities and those are now being pursued within the framework of director’s discretionary project. The following is the list of research institutions in the field of climate studies we are now collaborating with:

# Scripps Institution of Oceanography # Canadian Meteorological Office # Hadley Centre/CGAM # CNRS/IFREMER

Table 7-1. Hindcast simulation settings.

Model Setting of Model Setting of HindcastHindcast RunRun

Model : OFES (OGCM for the Earth Simulator)Computational domain : 75S-75NHorizontal grid spacing : 0.1°

Number of vertical levels : 54 (20 levels in 200m depth)Bathymetry : 1/30°OCCAM data set Initial Condition : Annual mean temperature and salinity

fields (WOA98) without motionForcing : Daily mean NCEP/NCAR re-analysis

: Weak restoring to monthly SSS(WOA98)Boundary condition : Restoring to monthly temperature and

salinity fields(WOA98) at all levels near the north and south artificial boundaries

Parameterization : Bi-harmonic (Horizontal), KPP (Vertical)

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7.3. Collaborative high-resolution simulation researches relating to CLIVAR Atmospheric and oceanic simulation research group at ESC has been working together with

the researchers in Frontier Research System for Global Change who are interested in high-resolution climate simulations. Since eddy-resolving simulations on the global domain is an obvious target simulation for ES, we put the first priority on it and after 50 years-long spin-up experiment, we have successfully performed subsequent 50 years-long CFC tracer experiment and hindcast run covering from 1950 to 2003. The outline of our simulation settings for hindcast run is given in Table 7-1.

Since the outputs are still being analyzed, here we show a few key monitoring outputs obtained for the quality check of our simulation. In Fig. 7-2, as a well-known measure for eddy activity, we show the simulated sea surface height (SSH) variability obtained both through the spin-up and hindcast runs and compare them with the observation. A few leading simulation researches in this field already revealed the fact that at least 10 km horizontal resolution is necessary to reproduce realistic eddy activities measured through SSH variability and our simulation result is consistent with it and captures well the overall characteristics of the variability field though with the closer inspection we notice considerable discrepancy, say, in the shape of high eddy activity region of the Kuroshio.

Observation (T/P & ERS)

Eddy ActivityEddy Activity Spin-up Run

Hindcast Run

Fig. 7-2. Sea surface height variability.

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In our hindcast run, as you see in Table 7-1, temperature restoring is not applied to the upper

boundary and the temperature is calculated based on the energy equation at the surface. We have looked into the behaviors of our simulated Niño3 SST anomaly and recently-documented IOD index together with the associated Hovmoller diagram of SST, which are given in Fig. 7-3. Remarkable reproducibility of the both indices in our simulation encourage us to pursue high-resolution simulation studies further and we believe that our hindcast run could be a valuable simulation data source through which many dynamical aspects of the ocean physics can be studied. 7.4. Perspective on high-resolution simulation researches

As was mentioned in Section 7.2, ESC is a unique climate simulation center which hosts leading high-resolution simulation research groups in the world. We can say that the years 2002 and 2003 are preliminary test period for the non-ESC users and we believe that the simulation research outcomes of those outer users are gradually emerging soon. In the previous section, we provided a promising evidence for high-resolution oceanic simulation as an example of such studies. Presumably, one of the big problems in executing high-resolution run is the time consuming data handling, which could be the main cause of the delay of the planned researches. However, ESC recently introduced a new mass data processing system (MDPS) and will be connected to the fast data transfer network system called super SINET, which will surely improve the situation and help ES users to accelerate their simulation researches.

-3

-2

-1

0

1

2

3

4

58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94

Nor

mal

ized

Anom

aly

-3

-2

-1

0

1

2

3

4

58 60 62 64 66 68 70 72 74 76 78 80 82 84 86 88 90 92 94

NIN

O3 S

ST A

nom

aly(

℃）

El Nino and Indian Ocean DipoleSea Surface Temperature Anomaly

along EquatorNino3 SST Anomaly

(Observation: Purple, Simulation: Blue)

Normalized Dipole Mode Index smoothed by five-month Running Mean

(Observation: Purple, Simulation: Blue)Positive IOD(72)

Negative IOD(73)

CORR.= 0.850

CORR.= 0.733

Fig. 7-3. ENSO and IOD indices.

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8. SAGE (SubArctic Gyre Experiment)

The SAGE project (SubArctic Gyre Experiment) had been conducted during 1997-2001 for the purpose of elucidating the hydrographic structure, variability and roles on climate in the North Pacific Subarctic regions. Special emphases were on the basin wide observation of P1 reoccupation as well as North Pacific Intermediate Water (NPIW). P1-observation revealed decadal changes of North Pacific intermediate-deep waters. Intensive observations in the Okhotsk Sea, western subarctic Pacific and the areas east of Japan have provided the transport distributions relating to NPIW and revealed the existence of the cross-wind-driven gyre Oyashio water transport that flows directly from the subarctic to subtropical gyres through the western boundary current as well as the diffusive contribution across the subarctic front. The anthropogenic CO2 transport into NPIW has been estimated. The northern part of NPIW in the Transition Domain east of Japan is transported to the Gulf of Alaska, feeding the mesothermal (intermediate temperature maximum) structure in the North Pacific subarctic region where deep convection is restricted by the strong halocline maintained by the warm and salty water transport originating from NPIW. This heat and salt transport is mostly balanced by the cooling and freshening in the formation of dense shelf water accompanied by sea-ice formation and convection in the Okhotsk Sea. Intensive observational and modeling studies have substantially altered our view of the intermediate-depth circulation in the North Pacific. NPIW circulations are related to diapycnal-meridional overturning, generated around the Okhotsk Sea due to tide-induced diapycnal mixing and dense shelf water formation accompanied by sea-ice formation in the Okhotsk Sea. This overturning circulation may possibly explain the direct cross-gyre transport through the Oyashio along the western boundary from the subarctic to subtropical gyres. Air-sea CO2 flux studies and quantitative estimate of biological pump by Calanus spieces that undergo seasonal vertical migration were also reported.

These studies were already published in wide variety of journals. Two special issues were also published. For details of the special issues and review, please see Journal of Oceanography, 2003, 59(6), 853-945 and 2004, 60(2), in press.

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9. Kuroshio Fluctuation Prediction Experiment

The Kuroshio is one of the strongest currents in the world oceans, flowing northeastward south of Japan as the western boundary current (WBC) of the North Pacific Subtropical Gyre (NPSG). Its heat transport is crucial to maintaining the global climate. Its location and flow field affect the fisheries, marine transportation, marine sports, etc. and so the Kuroshio has attracted the attention of many people. The Kuroshio is noted especially for a unique phenomenon: the stationary large meander south of Honshu, Japan. The real flow field in and around the Kuroshio, however, is very complicated due to its interactions with mesoscale eddies, warm rings, cold rings and other fluctuations. It has therefore turned out to be very difficult to predict the Kuroshio.

The recent progress in satellite remote sensing for earth observation is quite remarkable; the sea-surface topography, sea-surface temperature, sea-surface wind and other properties have been measured globally and repeatedly. Remarkable progress has been also made in the in situ observation of the Kuroshio; thanks to the field program entitled “Affiliated Surveys of the Kuroshio off Cape Ashizuri” (ASUKA), a time series of Kuroshio transport has become available, for the first time, with a fairly fine temporal resolution covering a relatively long period (Imawaki et al., 2001). In ocean modeling, high-resolution ocean general circulation models have been developed and the technique of data assimilation has also become available to provide dynamically consistent data sets, or state estimation.

Based on the recent progress mentioned above, an experiment was carried out to challenge the prediction of fluctuations of the location and transport of the Kuroshio south of Japan, which has been a dream for many years. A research team was organized by scientists from Kyushu Univ., Kagoshima Univ., Hiroshima Univ., Kyoto Univ., Univ. Tokyo, Hokkaido Univ. and Meteorological Research Institute, to develop a system for predicting the Kuroshio fluctuation and to assess the possibility of prediction. This experiment was called “Kuroshio Fluctuation Prediction Experiment” and was carried out for five years from 1997 to 2002 as a research program of the Core Research for Evolutional Science and Technology (CREST) of Japan Science and Technology Corporation (JST).

The experiment had four aims: (a) collecting ocean variability data on the Kuroshio and western NPSG regions to better understand the variability and its mechanism as well as to provide the data for validation of the state estimation; (b) developing a data assimilation model to provide dynamically consistent data sets from observation data; (c) developing a high-resolution prediction model using those data sets as initial and boundary conditions; and also (d) developing a practical prediction model by incorporating the data assimilation model and prediction model. Two specific predictions were targeted: the short-range (one month) prediction of the location of the Kuroshio path south of Japan, and the medium-range (one to two years) prediction of the Kuroshio transport south of Japan. The experiment was intended

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to stimulate understanding the mechanism underlying the Kuroshio fluctuations through these predictions. Path fluctuation

The path of the Kuroshio south of Japan is usually classified into two stable paths: the large meander path and the non-large meander path (Kawabe, 1995). Small meanders originating south of Kyushu frequently propagate eastward south of Japan. An occasional small meander happens to develop into the stationary large meander. It has been suggested that mesoscale eddies play an important role in this phenomenon. The Kuroshio did not take the stationary large meander path during the present research program. The following progress was made in the study of the Kuroshio path fluctuations, thanks to this program.

The surface flow field obtained by combing the satellite altimeter data and surface drifting-buoy data provided a vivid description of the variability of the Kuroshio and Kuroshio Extension (Uchida and Imawaki, 2003; Imawaki et al., 2003). Based on this flow field, the Kuroshio axis was detected by tracking the location of the locally strongest velocity in the Kuroshio region (Ambe et al., 2004). Fig. 9-1 is the superposition of Kuroshio axes south of Japan obtained every 10 days for eight years from 1993 to 2000. This is the first data set to describe the variation of the Kuroshio axis with a fairly fine resolution both in time and space. Further, it was shown that fluctuations of the Kuroshio path in the Tokara Strait are induced both by disturbances propagating from the East China Sea (i.e., the upstream region) and by mesoscale eddies propagating from the western part of the NPSG at about 30°N latitude (Ichikawa, 2001). Fluctuations of the Kuroshio path in the East China Sea between the continental slope and the Tokara Strait was also studied in detail (Nakamura et al., 2003).

Fig. 9-1. Super- position of Kuroshio axes south of Japan detected every ten days from 1993 to 2000 (Ambe et al., 2004). The Kuroshio axis was detected by tracking the location of the locally strongest velocity in the surface flow field of the Kuroshio region, which was obtained by combing the satellite altimeter data and surface drifting-buoy data. Contours show depths of 500 m and 1000 m.

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Studies on predicting fluctuations of the Kuroshio path south of Japan were carried out as

follows. A reduced-gravity model was used to assimilate the satellite altimeter data by an adjoint model, which has an advantage in reproducing non-linear phenomena. Experiments using thus-obtained assimilated data as the initial condition showed that the Kuroshio path can be predicted for about two months (Ishikawa et al., 2004). Further, state estimation was carried out by assimilating the satellite altimeter data into an ocean general circulation model for the whole North Pacific, driven by observed daily wind stress; here a four-dimensional optimal interpolation was used in the assimilation process (Kamachi et al., 2004a). The results obtained compared well with the flow field of the western NPSG observed by a ship-mounted acoustic Doppler current profiler (Kaneko et al., 2001) and moored current meters (Ichikawa, H. et al., 2004). Using this state estimation as the initial condition, a practical prediction model was developed to hindcast locations of the Kuroshio path; a number of experiments were carried out by choosing different starting dates, and the results showed that the prediction was successful for about one month (Kamachi et al., 2004b).

The transition mechanism between the large meander path and non-large meander path of the Kuroshio south of Japan was studied. First, the role of the wind stress field of the North Pacific in determining these two stable paths was investigated using an idealized two-layer model (Kurogi and Akitomo, 2003). A sensitivity experiment was then carried out with the same two-layer model, showing that mesoscale eddies located initially south of Kyushu or east of Taiwan induced the transition from non-large meander path to large meander path, but did not induce the opposite transition (Akitomo and Kurogi, 2001). A simulation experiment using a high-resolution ocean general circulation model confirmed that the interaction between the Kuroshio and mesoscale eddies was crucial for the variation of the Kuroshio path south of Japan, including the transition between the two stable paths; a possible mechanism of the generation of small meanders of the Kuroshio south of Kyushu was studied in detail (Masumoto, 2004). Transport fluctuation

The transport of the Kuroshio as the WBC of the NPSG is mostly determined by the wind stress over the North Pacific. In the steady state, the transport can be estimated as the transport of WBC compensating the interior Sverdrup transport, which is the wind-induced transport based on the linear theory for an ocean with flat bottom topography; the transport of WBC thus estimated is hereafter called Sverdrup transport for simplicity. The wind stress, however, varies having various time scales, and the corresponding time scales of oceanic response are different. Therefore, the transport of WBC cannot be understood simply as the Sverdrup transport. The bottom topography, such as the Izu-Ogasawara Ridge, induces interference between the barotropic and baroclinic components of the flow field, and makes the situation more complicated. In practice, excluding the transport associated with mesoscale

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eddies is also a serious issue. The following progress was made in the study of the Kuroshio transport fluctuations, thanks to the present research program.

A very high correlation has been found between the Kuroshio transport (for upper 1,000 m layer) and sea-surface height difference across the Kuroshio (Imawaki et al., 2001), on the basis of intensive ASUKA observations. Using this relationship and TOPEX/POSEIDON satellite altimeter data, the transport of the Kuroshio south of Shikoku, Japan, was estimated for ten years from 1993 to 2002 (Uchida and Imawaki, 2004). The result is shown in Fig. 9-2. This is the first time series of Kuroshio transport obtained for a long period. The mean transport of the eastward-flowing Kuroshio was estimated to be 61 Sv (1 Sv = 106 m3/sec), and that of the Kuroshio through-flow was 43 Sv, excluding the local recirculation.

The mean seasonal signal of Kuroshio transport estimated from this ten-year long time series was fairly weak compared with that of the Sverdrup transport estimated from the observed wind stress over the North Pacific (Uchida and Imawaki, 2004). To understand the difference, the ocean response to the seasonally varying wind stress was studied using an idealized two-layer ocean model. The results showed that the bottom relief corresponding to the Izu-Ogasawara Ridge prevents most of the barotropic signal, originated in the interior region, going beyond the relief, and therefore the seasonal signal of Kuroshio transport is much reduced (Isobe and Imawaki, 2002). The seasonal signal in the flow field west of the Ridge was further studied in detail (Isobe et al., 2004).

Fig. 9-2. Time series of the Kuroshio transport (solid line with dots; in Sv) south of Japan during 1992-1999, estimated from TOPEX/POSEIDON altimeter data using the relationship between the transport and SSDT difference (Uchida and Imawaki, 2004). Panel (a) is the transport of the eastward flowing Kuroshio. Also shown are transports (circles) estimated from in situ data. Panel (b) is the throughflow transport of the Kuroshio.

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In regard to the interannual fluctuation of Kuroshio transport, the exchange among vertical modes of the flow field due to the Izu-Ogasawara Ridge was found to be important (Tanaka and Ikeda, 2004). Data sets of the wind stress over the North Pacific, used to drive ocean general circulation models, were examined in detail (Yoshinari et al., 2004). An investigation was made on where in the NPSG the major origin of the Kuroshio transport fluctuations having time scales of 2-3 years was located (Wakata et al., 2004). Further, a study on the predictability of the interannual fluctuation of Kuroshio transport was carried out, in the fashion of a hindcast, as follows: An ocean general circulation model for the North Pacific was driven by an observed time series of wind stress having interannual fluctuations. The wind stress was then fixed at a given time and the model continued to be driven by that fixed wind stress. The Kuroshio transport thus calculated was compared with that in the model driven continuously by the original time series. The study showed that most of the interannual fluctuation of Kuroshio transport can be predicted for one to two years, using only the past record of time series of the wind stress over the North Pacific (Tanaka et al., 2004).

A discrepancy had been recognized in the Kuroshio transport, which is about 40 Sv (Imawaki et al., 2001) south of Shikoku, Japan, and about 20 Sv in the East China Sea (Ichikawa and Chaen, 2000). This can be probably accounted for by the northeastward flow over the continental slope east of the Ryukyu Islands (i.e., the upstream region of the Kuroshio south of Japan), which was detected by the moored current meter observations during 1998-2002 and TOPEX/POSEIDON satellite altimeter data (Ichikawa, H. et al., 2004). The flow was found to be confined over the slope and consist of a surface mode and a subsurface-core mode centered at about 600 m depth. The four-year mean transport was estimated to be 16-18 Sv. These results suggest that a new boundary current, which might be called the “Ryukyu Current System”, exists east of the Ryukyu Islands and thus of schematic flow field of the Kuroshio system proposed by Nitani (1972) deserves revision in this light.

The flow field of the western NPSG was further measured by a ship-mounted acoustic Doppler current profiler (Kaneko et al., 2001). The measured instantaneous surface velocities were combined with the satellite altimeter data to provide the mean surface velocities along the ship tracks (Ichikawa, K. et al., 2004). The results can be used to monitor the surface flow field continuously using satellite altimeter data.

As described above, considerable progress has been made in understanding the fluctuations in the location and transport of the Kuroshio south of Japan, thanks to the present research program. The latest ocean general circulation model incorporated with the data assimilation model was shown to be able to predict those fluctuations to some extent. Further progress is required, however, for those prediction systems to gain acceptance in our daily life.

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References

Akitomo, K. and M. Kurogi (2001): Path transition of the Kuroshio due to mesoscale eddies: A two-layer, wind-driven experiment. J. Oceanogr., 57, 735-741.

Ambe, D., S. Imawaki, H. Uchida and K. Ichikawa (2004): Estimating the Kuroshio axis south of Japan using combination of satellite altimetry and drifting buoys. J. Oceanogr., 60 (in press).

Ichikawa, H. and M. Chaen (2000): Seasonal variation of heat and freshwater transports by the Kuroshio in the East China Sea. J. Marine Systems, 24, 119-129.

Ichikawa, H., H. Nakamura, A. Nishina and M. Higashi (2004): Variability of northeastward current southeast of northern Ryukyu Islands. J. Oceanogr., 60 (in press).

Ichikawa, K. (2001): Variation of the Kuroshio in the Tokara Strait induced by meso-scale eddies. J. Oceanogr., 57, 55 –68.

Ichikawa, K., N. Gohda, M. Arai and A. Kaneko (2004): Monitoring surface velocity from repeated ADCP observations and satellite altimetry. J. Oceanogr., 60 (in press).

Imawaki, S., H. Uchida, K. Ichikawa and D. Ambe (2003): Estimating the high-resolution mean sea-surface velocity field by combined use of altimeter and drifter data for geoid model improvement. Space Sci. Rev., 108, 195-204.

Imawaki, S., H. Uchida, H. Ichikawa, M. Fukasawa, S. Umatani and the ASUKA Group (2001): Satellite altimeter monitoring the Kuroshio transport south of Japan. Geophys. Res. Lett., 28, 17-20.

Ishikawa, Y., T. Awaji, N. Komori and T. Toyoda (2004): Application of sensitivity analysis using an adjoint model for short-range forecasts of the Kuroshio path south of Japan. J. Oceanogr., 60 (in press).

Isobe, A. and S. Imawaki (2002): Annual variation of the Kuroshio transport in a two-layer numerical model with a ridge. J. Phys. Oceanogr., 32, 994-1009.

Isobe, A., M. Kamachi, Y. Masumoto, H. Uchida and T. Kuragano (2004): Seasonality of the Kuroshio transport revealed in a Kuroshio assimilation system. J. Oceanogr., 60 (in press).

Kamachi, M., T. Kuragano, H. Ichikawa, H. Nakamura, A. Nishina, A. Isobe, D. Ambe, M. Arai, N. Gohda, S. Sugimoto, K. Yoshita, T. Sakurai and F. Uboldi (2004a): Operational data assimilation system for the Kuroshio south of Japan: Reanalysis and validation. J. Oceanogr., 60 (in press).

Kamachi, M., T. Kuragano, S. Sugimoto, K. Yoshita, T. Sakurai, T. Nakano, N. Usui and F. Uboldi (2004b): Short-range prediction experiments with operational data assimilation system for the Kuroshio south of Japan. J. Oceanogr., 60 (in press).

Kaneko, A., Z. Yuan, N. Gohda, M. Arai, H. Nakajima, H. Zheng and T. Sugimoto (2001): Repeat meridional survey of the western North Pacific subtropical gyre by a VOS ADCP during 1997 to 1998. Geophys. Res. Lett., 28, 3429-3434.

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Kawabe, M. (1995): Variation of current path, velocity, and volume transport of the Kuroshio in relation with the large meander. J. Phys. Oceanogr., 25, 3103-3117.

Kurogi, M. and K. Akitomo (2003): Stable paths of the Kuroshio south of Japan determined by the wind stress field. J. Geophys. Res., 108(C10), 3332, doi:10.1029/2003JC001853.

Masumoto, Y. (2004): Generation of small meanders of the Kuroshio south of Kyushu in a high-resolution ocean general circulation model. J. Oceanogr., 60 (in press).

Nakamura, H., H. Ichikawa, A. Nishina, and H.–J. Lie (2003): Kuroshio path meander between the continental slope and the Tokara Strait in the East China Sea. J. Geophys. Res., 108(C11), 3360, doi: 10.1029/2002JC001450.

Nitani, H. (1972): Beginning of the Kuroshio. p.129-163. In "Kuroshio: Its Physical Aspects", ed. by H. Stommel and K. Yoshida, University of Tokyo Press.

Tanaka, K. and M. Ikeda (2004): Propagation of Rossby waves over ridges excited by interannual wind forcing in a western North Pacific model. J. Oceanogr., 60 (in press).

Tanaka, K., M. Ikeda and Y. Masumoto (2004): Predictability of interannual variability in the Kuroshio transport south of Japan based on wind stress data over the North Pacific. J. Oceanogr., 60 (in press).

Uchida, H. and S. Imawaki (2003): Eulerian mean surface velocity field derived by combining drifter and satellite altimeter data. Geophys. Res. Lett., 30(5), 1229, doi:10.1029/2002GL016445.

Uchida, H. and S. Imawaki (2004): Ten-year record of the Kuroshio transport south of Japan estimated from satellite altimeter data. in preparation.

Yoshinari, H., M. Ikeda, K. Tanaka and Y. Masumoto (2004): Sensitivity of the interannual Kuroshio transport variation south of Japan to wind dataset in OGCM calculation. J. Oceanogr., 60 (in press).

Wakata, Y., T. Setou, I. Kaneko, H. Uchida and S. Imawaki (2004): Interannual variability of the Kuroshio transport in an OGCM related to the North Pacific windstress. J. Oceanogr. (submitted).

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10. Study of the Sea of Okhotsk

It is well known that the Sea of Okhotsk is one of the southernmost seasonal sea ice zones in the Northern Hemisphere. Recently, it is noticed that the Sea may be an origin of the North Pacific Intermediate Water (NPIW) and regions for the absorption of carbon dioxide and the high biological productivity. However, very few oceanographic observations have been made in the Sea of Okhotsk. 10.1 Japan-Russia-United States joint project (1997-2002)

In this project, we have done intensive observations in almost all regions of the Sea of Okhotsk with four times cruises aboard R/V Professor Khromov, and obtained lots of valuable observational results. Parts of them for physical oceanography are as follows; (1) The ocean circulation is entirely composed of cyclonic and anticyclonic gyres in the northern and southern regions, respectively. Fig. 10-1 is a schematic illustration and the circulation and mesoscale features derived from the surface drifter data.

Fig. 10-1. Schematic of near-surface circulation for the Sea of Okhotsk as derived from our satellite-tracked drifter data. Thicker arrows represent the stronger flow. Currents in the eastern part are

depicted by dotted lines because they are based on speculation.

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(2) The drifters clearly revealed the existence of the southward boundary current off the east Sakhalin. This current (the East Sakhalin Current) is strongly controlled by bottom topography. The East Sakhalin Current appears to consist of two cores; one exists near the coast (50-150 m depths) extending toward the southern tip of the Sakhalin Island, and the other over the shelf slope (300-900 m depths) turning to the east around Terpeniya Bay and flowing eastward as far as Bussol Strait. (3) Long-term mooring measurements clearly revealed the structure and seasonal variability of the East Sakhalin Current. Its southward flow extended from the surface to a depth around 1000 m. The total volume transport of the East Sakhalin Current at 53°N was 6.7 Sv in the annual average, varying from a maximum of 12.3 Sv in February and a minimum of 1.2 Sv in October. (4) In the northwestern coastal polynya region, moored winter observations evidently took linear salinization of shelf water due to brine rejection; this is the first direct measurement of NPIW in the Sea of Okhotsk. (5) Estimation of the average DSW flux was newly made to be 0.6 Sv in the range of 26.7-27.0σθ, using the historical bottle data and recent CTD data and 0.67 Sv in the range of 26.75-27.05σθ, using a climatological dataset, respectively. (6) Using two moorings at 53°N for a year period in 1998-1999, the average DSW transport for σθ > 26.7 was evaluated to be nearly 0.21 Sv. Both the relatively low DSW transport evaluated at 53°N and onshore eddy heat flux observed at moorings off northern Sakhalin suggest that DSW transport occurs not only in the form of a southward coastally-trapped flow associated with the ESC but also offshore eddy transport. (7) An outflow from the Sea of Okhotsk to the North Pacific was measured at the Bussol Strait using yo-yo casts (13 stations) of LADCP. The diurnal tide at the spring tide showed a remarkable peak of the amplitude of 1.1 ms-1 at the depth below 1000 m in the western channel of the strait. The outflow is in excess of the inflow and net transport through the strait was 8.2 to 8.8 Sv. The outflow was strong in two density ranges. The upper layer peak around 26.8σθ

corresponds to the density of NPIW. (8) Net heat and salt exchanges between the Sea of Okhotsk and the North Pacific were estimated; net heat flux of -34 TW and net salt flux of -1.9 x 106 kgs-1 were exchanged from the Sea of Okhotsk to the North Pacific. 10.2. Amur-Okhotsk Project (2005-2010)

We are planning to have Japan-Russia-China-other countries joint project assessing the human impacts in the Amur River basin on the marine ecology in the Sea of Okhotsk and northern North Pacific (see Fig. 10-2) for next five years. The key element supporting the biomass production in the Sea of Okhotsk is considered to be "dissolved iron" from the Amur River. Primary goal of the project is, therefore, to elucidate the mechanism how the dissolved iron and fulvic acids are formed and transported to the ocean both by the Amur River and

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through the atmosphere, and how the flux changes will affect the phytoplankton production in the Sea of Okhotsk and the northern North Pacific. We will then clarify the anthropogenic impacts on the flux changes to the ocean.

Fig. 10- 2. Schematic image of the AMUR-OKHOTSK PROJECT

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11. Argo project in Japan 11.1. Introduction

International Argo project was planned as a major component of the ocean observing system and has been showing its capability since the beginning of Argo float deployment in 2000. Argo is essential to carry out researches in the CLIVAR-GOALS because it develops observational capabilities to describe seasonal and interannual climate variability in the upper ocean. By 2006, 3000 Argo floats will be expected to work in the world ocean. 11.2. Domestic organizations to conduct Argo and the objectives

In Japan, Argo has been conducted as one of “Millennium Projects” since April 2000 with the cooperation of two ministries, MEXT (JAMSTEC) and MLIT (JMA and JCG).

Argo project in Japan has been establishing the Argo network in cooperation with other nations and developing various techniques as follows; 1) to deploy as many Argo floats as possible, 2) to develop a numerical model to simulate the dispersion of Argo floats after deployment, 3) to examine long term stability of CTD sensors loaded on Argo floats by recovery of floats operating at sea, 4) to improve the launching device of Argo float from cruising vessels, 5) to establish the data distribution system in real time mode and delayed mode, 6) to develop scientific quality control procedure for salinity measurements in delayed mode, 7) to develop assimilation models to effectively utilize Argo float data, 8) to improve the numerical forecasting model and to get a higher reliability of forecasted SST.

Argo floats have been deployed by 14 research vessels belonging to JAMSTEC, JMA, JCG, JFA, NPRI, ORI, Hokkaido Univ., and TUMST. Misaki Fishery high school will join in this float deployment fleet from October 2004.

*MEXT: Ministry of Education, Culture, Sports, Science and Technology *MLIT: Ministry of Land, Infrastructure and Transport *JMA: Japan Meteorological Agency *JCG: Japan Coast Guard *JFA: Japan Fishery Agency *NPRI: National Polar Research Institute *ORI: Ocean Research Institute, University of Tokyo *TUMST: Tokyo University of Marine Science and Technology *JAMSTEC: Japan Marine Science and Technology Center

11.3. Deployment of Argo floats

As of February 2004, 1043 Argo floats deployed by 17 nations and EU are actively working

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in the world ocean (Fig. 11-1). Among 1043 ago floats, Japan deployed 181 Argo floats which is the second largest contribution to the international Argo project. The Beagle 2003 cruise of the research vessel Mirai of JAMSTEC which made around the globe observation in the southern hemisphere between August 2003 and March 2004 played an important role to fill the sparse area of Argo float distribution in the hemisphere by deploying 28 Japanese Argo floats, 19 US and 15 UK Argo floats.

The total number of Argo floats deployed by Japan amount to 283 since 2000. Japan (JAMSTEC) will continue to deploy Argo floats through FY2008 after the termination of Millennium Projects in March 2005.

11.4. Technical issues Since the Argo project was started in Japan in 2000, we, Japanese Argonauts have

encountered several technical issues with Argo floats, and at present we think that it is necessary to solve any technical issues when experienced and to get current floats more suitable for the Argo project. Taking an example of technical issues we encountered, we have struggle to trace the salinity offset issue with PROVOR/Metocean floats in cooperation with the float maker, the sensor maker and scientists and engineers of SIO, University of Washington, and IFREMER and finally we solved the issue, which was an important contribution to world Argo community. Furthermore in order to examine the long term trend of the salinity measurement accuracy, we have tried seven times to retrieve the Argo floats which were operating at sea and at all times succeeded in it. This kind of “active” retrieval of Argo floats is very important and has been hardly tried by Argonauts of any other nations.

Fig. 11-1. Distribution of Argo floats as of February 2004.

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・ NDAC(National Data Assembly Center)：　JMA　GDAC(Global Data Assembly Center)：　FNMOC & IFREMER

AIC: Argo Information Center　All Argo data is filed in netCDF format

PIs

NDAC

Reginal CenterGTS

Users

Mirroring site of GDAC

Delayed mode Real time mode

GDAC

rQC

dQC

d2QC

meta dataprofile data (R,D)trajectory datatechnical data

Argo　Data　Flow

Worldwide Met.Agencies

AIC

Real time data

Delayed mode data

JAMSTEC

Fig. 11-2. Argo data flow system.

11.5. Distribution and quality control of Argo float data

The fundamentals of Argo data distribution are the real time distribution for worldwide meteorological organizations and several months delayed distribution of scientific quality controlled data for scientific users absolutely with no charge and no limitation of users.

The Japan Meteorological Agency (JMA) serves as the Japan NDAC issuing Argo data to the GTS in TESAC form within nearly 24 hours after acquisition of Argo data via the Argos system and to the GDACs after real time QC as well (Fig. 11-2).

JAMSTEC makes the delayed mode quality control for the data from Argo floats deployed by Japanese PIs (JAMSTEC, NPRI, and Tohoku University) and is expected to issue them to GDACs within 6 months after acquisition of data from Argo floats. JAMSTEC is mirroring the GDAC ftp sites as well.

Various information on the Argo float data such as the global network, float tracks, T-S profiles, T-S diagrams, and scientific products is available on the web page of JMA and JAMSTEC (http://www.jamstec.go.jp/J-ARGO/index_e.html).

Comparing salinity measurements of Argo floats with local climatological data especially in deep layers is one of the most realistic methods for examining measurement accuracy, and a new method was developed by PMEL/NOAA and adopted as an Argo standard. JAMSTEC’s experiments clarified that this standard method has the sufficient potential to correct float salinity measurements within ±0.01 psu, only when the suitable climatological datasets are used (Fig. 11-3). Thus, JAMSTEC produced a reference dataset necessary to correct Argo salinity measurements in the Pacific and the Indian Ocean.

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1500dbar or moreAt least

2000dbar

Within 0.01psu errors by 1000dbar profiles

2000dbar constant1500dbar constant1000dbar constant

Riser scheme

Fig. 11-3. Dependency of salinity correction errors upon observational regions and profiling depths

(Kobayashi and Minato, submitted to J. Atmos. and Oceanic Tech.) 11.6. Data analysis

An analysis of Argo float data in the late winter of 2003 revealed the formation region of the North Pacific Subtropical Mode Water (NPSTMW) extends south of the Kuroshio Extension, between 30°N and 35°N and as far east as 175°E and the spatial variation of the mixed layer depth in the region corresponds well with the underlying permanent thermocline depth (Fig. 11-4). Other analysis of Argo float data verified that mesoscale eddies play an important role in the formation and transport of NPSTMW in the recirculation region of the Kuroshio. The North Pacific Central Mode Water (NPCMW) has been observed by using isopycnal Argo floats which drift along the bottom of the NPCMW. 11.7. Assimilation and prediction

A 4DVAR data assimilation system consisting both with a dynamic oceanographic model and with observational data has been developed to create a 3-dimensional grid dataset from sparsely measured Argo data. Assimilation experiments have been carried out using the Argo data from 2001 to 2002 and a global ocean model with the resolution of 1°x1° in horizontal and 36 levels in vertical. A comparison of the simulated and assimilated ocean states reveals that temperature and salinity fields are improved fairly well by use of Argo data.

JMA has been developing numerical forecasting models to get SST distribution in a higher reliability concerning the prediction of El Nino event.

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>200db

SST (ºC)

MLD (db)

Fig.4 Distribution of SST and mixed layer depth observed by Argo floats east of Japan in

February-March 2003 (Oka and Suga, 2003). 11.8. International cooperation (1st Science Workshop)

The First Argo Science Workshop cosponsored by JAMSTEC and NOAA was held in Tokyo in November 12-14, 2003. This was very successful to demonstrate the early achievements of Argo and the present and likely future value of Argo for a wide range of applications. More than 200 scientists and engineers attended this workshop including 99 attendees from 22 foreign nations.

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12. Japan GODAE Activities

12.1. Background In order to activate Japan GODAE activities, three working groups (WGs) have been

established. The first of these is placed at the Science Council of Japan with an emphasis on more appropriate directions and recommendations for scientific and operational developments. The second WG is under the Japan CEOS/IGOS-Ocean Committee in the Japan Aerospace Exploration Agency (JAXA), whose objective is to enhance linkages between data flow/product and assimilation experiments. The third WG is for J-GODAE High Resolution SST project (ADEOS-II New Generation SSTs) by the Earth Science and Technology Forum (ESTF) under Earth Science and Technology Organization (AESTO), which plays a key role in developing Japan-GODAE High Resolution SST. These WGs consist of university members (Kyoto, Tohoku, Hokkaido, Tokai, Kyushu, and Tokyo) and Agency members such as JAMSTEC, JAXA, RESTEC, CRIEPI, Frontier groups (FRSGC/IGCR, FRSGC/IMRP, FORSGC, and IPRC), JCG, JFA and JMA.

These activities of the WGs will build on and develop links with existing activities, such as for the delivery of quality-controlled data in both real-time mode (from JMA) and intermediate-time mode (from JAMSTEC), the archiving of all observational data at JODC (the National Oceanographic Data Centre), and the delivery of satellite data from JAXA. Such Japan GODAE activities are supported by the ongoing research initiatives esp. Millennium Project (Japan-Argo), RR2002 Project, CLIVAR/UOP, and CLIVAR/PBECS.

The WGs will establish a “Japan-GODAE Network” with an aim at strengthening mutual links among research, technical information, data delivery, and distribution of products to users. The main Japanese contribution to International GODAE depends largely on the activities of the Japan Meteorological Agency, Frontier groups, and University groups as described below. 12.2. Japan-GODAE Consortium 12.2.1. Japan Meteorological Agency (JMA)/Office of Marine Prediction (OMP) and Meteorological Research Institute (MRI): COMPASS-K Model: The ocean model used is an MRI eddy permitting model (MRI-EGCM). The model is a rigid-lid version in the North Pacific from 12°N to 55°N. The grid has a variable mesh size: 1/4°x1/4°, and 21 vertical levels around Japan. The model includes Takano-Oonishi scheme for treating steep bottom topography with generalized Arakawa scheme for momentum advection terms. A new community model, MRI.COM, is now used for developing next generation of the operational system. Assimilation Method: The assimilation system uses a multivariate, scale-dependent four-dimensional optimum interpolation (4DOI) method with a preceding-nudging insertion (Kamachi et al., 2001). The OI employs inhomogeneous, anisotropic space-time combined

49

background error covariance analyzed by Kuragano and Kamachi (2001) for TOPEX/POSEIDON altimetry. The method will be improved to be a reduced space 3DVAR-IAU method for salinity, with a nonlinear descent method (POpULar). Input Data: In-situ data; GTS data with JMA QC procedures applied, Altimetry; TOPEX/POSEIDON and Jason-1, SST; JMA OI-analysis with satellite and ship data. It will be changed to J-GODAE High Resolution SST produced by Tohoku University and JAXA for research version and by JMA for operational version. Products: State variables through JMA GODAE product server and NEARGOOS data server (RRTDB). Targeted Users: Ocean research community and other agencies (e.g. Japan Coastal Guard, Japan Fisheries Agency). 12.2.2. JMA/Climate Prediction Division (CPD): ODAS Model: The ocean model is a JMA-OGCM. The model is a rigid-lid version in the global ocean. It includes a nonlinear dissipation scheme with deformation fields. Mixed layer scheme is the Mellor-Yamada’s turbulent closure scheme, level 2.5. The grid is a variable grid, 2.0°x2.5°, 20 vertical levels, and 0.5°x2.5° around equator. The model will be changed to new community model, MRI.COM.

Fig. 12-1. Schematic View of Japan GODAE Consortium

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Assimilation Method: The assimilation system uses Derber-Rosati type 3DVAR with ship and TAO-TRITON temperature and TOPEX/POSEIDON and Jason-1 altimeter data. The observation error covariance is proportional to the vertical gradient of the temperature. Salinity assimilation will be performed in the next version. The method will be changed to a reduced space 3DVAR-IAU method with a nonlinear descent method (POpULar). Input Data: Forcing data; JMA-NWP real time analysis (NuSDaS), In-situ data; GTS with JMA QC procedures applied, TAO-TRITON data , and Argo’s T-S data, Altimetry; TOPEX/POSEIDON (and Jason-1) altimetry will be used, SST; JMA OI-analysis with satellite and ship data. Products: SST data through internet. Targeted Users: Supply of Initial condition to seasonal-to-interannual prediction with a coupled GCM. 12.2.3. Kyoto University and Japan Marine Science Foundation (MSF) Model: The ocean model is a KYOTO OGCM, which is similar to MRI and CCSR OGCM but a free-surface version that covers the global ocean. The sigma-z hybrid vertical coordinate is adopted. It includes Takano-Oonishi scheme for treating steep bottom topography with generalized Arakawa scheme for momentum advection terms and 3rd-order tracer advection terms. The Noh’s mixed layer and Gent-McWillams eddy parameterization schemes are adopted. Assimilation Method: The assimilation system uses a four-dimensional variational (4DVAR) method. Input Data: Forcing data; COADS dataset (da Silva, 1994) and OMIP dataset (based on ECMWF reanalysis, Roske 2001), In-situ data; World Ocean Atlas 94 (Temperature, salinity, SST and SSS) and WOCE Climatological dataset (Gouretski and Jancke, 1999), Altimetry; TOPEX/POSEIDON and Jason-1 altimetry. Products: Self-consistent dynamical dataset Targeted Users: Climate research community (initial condition for seasonal-to-interannual prediction) 12.2.4. Frontier Group (1): Frontier Research System for Global Change (FRSGC)/Integrated Modelling Research Program (IMRP) and Kyoto University Model: The ocean model is a free surface version of MOM3. The current resolution is 1°x1°, 34 vertical levels but will been soon developed to be a resolution of 1/4°x1/4°, 34 level. Assimilation Method: The assimilation system uses a four-dimensional variational (4DVAR) method. The adjoint code is derived with the Tangent-linear and Adjoint Compiler (TAMC) of Giering and Kaminsky (1997) and partly by hand. Input Data: Forcing data; NCEP-monthly mean wind stress, in-situ data; Argo float and WOA01, Altimetry; TOPEX/POSEIDON and Jason-1.

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Products: Comprehensive dataset with high accuracy and good dynamical consistency. Reanalysis dataset in 1990’s. Targeted Users: Climate research community (particularly for understanding of 1990’s El Nino). 12.2.5. Frontier Group (2): Frontier Research System for Global Change (FRSGC)/ Climate Variations Research Program (CVRP): J-COPE Model: The ocean model is the Princeton Ocean Model (POM) with a sigma coordinate of 1/4°x1/4°, 21 vertical levels in the North Pacific Ocean. The regional model has a resolution of 1/12°x1/12°, 35 vertical levels with a one-way nesting to the North Pacific model. Assimilation Method: The altimeter data are converted to subsurface temperature and salinity fields with a correlation method. The assimilation system uses an optimum interpolation and IAU method. Input Data: Forcing data; heat flux and wind stress calculated from the NCEP-6hourly Reanalysis data, Altimetry; TOPEX/POSEIDON, Jason-1 and ERS-2 (and will be changed to Jason-1 in 2002). Products: Four dimensional state vectors in the Kuroshio region through internet and CD-ROM. Targeted Users: Ocean research community for Kuroshio variability and its prediction. 12.2.6. Kyushu University/Research Institute for Applied Mechanics (RIAM)/Dynamics Simulations Research Centre (DSRC) Model: An eddy resolving model coded at RIAM, Kyushu University will be used. The model named RIAMOM allows us to adopt free surface, Takano-Oonishi and generalized Arakawa schemes. The model covers entire Japan/East China Sea with a very high resolution of 1/12°x1/12° degree and 40 vertical levels. Assimilation Method: The assimilation method is a reduced-order Kalman filter with sufficient resolution for the mesoscale variability. Input Data: Forcing data; JMA-NWP wind stress and fluxes, In-situ data; Ship data in the Tsushima Strait for boundary condition, Satellite data; TOPEX/POSEIDON and Jason-1, ERS, and PALACE. Products: State variables through internet in future. Targeted Users: Nowcast and forecast communities of the Japan Sea (fisheries, agencies, and university researchers) 12.3. Data and Product Serving

Japanese contribution to GODAE data and product servers would be made by the Japan Meteorological Agency (JMA), Japan Oceanographic Data Centre (JODC) in the Japan Coast Guard (JCG), International Pacific Research Centre (IPRC), Japan Marine Science and Technology Centre (JAMSTEC) and National Space Development Agency of Japan (NASDA).

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Those groups are the candidates of the data and product servers, because they have operational or research-based data processing, delivery and analyses systems in both real-time and delayed modes. The activity of the product servers will build on and develop links with existing data centers, such as data centers at the JMA of real time delivery, JAMSTEC and IPRC of intermediate time delivery for research works, JCG/JODC as the National Oceanographic Data Centre, and NASDA of satellite data delivery. The data centers work with ongoing data processing and management initiatives esp., NEARGOOS Regional Real Time and Delayed Mode Databases operated by JMA (RRTDB) and JODC (RDMDB) and national and regional data centers of Argo operated by JMA and JAMSTEC. JMA operates a GODAE product server, which provides the outputs of an ocean data assimilation system (COMPASS-K) and the result of global high resolution sea surface temperature (GHRSST) analysis operationally.

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13. Model Developments in Japan at the Era of the Earth Simulator

13.1. Introduction

The Earth Simulator project was completed in March, 2002, and the Earth Simulator (ES) is being operated since April, 2002 (see Fig. 13-1 and Chapter 7). We are surprised at the performance. Its sustain speed is 37TFLOPS, more than 90 % of the cataloged speed (see Fig. 13-2). Furthermore, it was achieved by using a real application, the optimized version of CCSR/NIES AGCM.

At the same time, in order to promote use of the Earth Simulator, the Ministry of Education, Culture, Sports, Science, and Technology (MEXT) has started a new Research Initiatives of “Research Revolution 2002 (RR2002)”, where environmental research was included. Its programme is called as the Kyousei program. Kyousei is Japanese whose meaning is symbiosis. Its full name is “the Symbiosis of Earth, Nature and Mankind”. It consists of two major programs, one is the development of a new “Japan model” for the Global Warming Issue by using the Earth simulator and other is for the prediction of the water cycle variability. Brief explanation of these activities from a viewpoint of CLIVAR will be presented in the following section.

Fig. 13-1. Schematic picture of the Earth Simulator.

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Fig. 13-2. Chart of Top500

13.2. Model development in Kyousei project

Many research groups are participating in the Kyousei Project. First, CCSR (Center for Climate System Research), NIES (National Institute and FRSGC

(Frontier Research System for Global Change) are working together to develop a high resolution climate model (T106L56AGCM+1/4° by 1/6° L46 OGCM) to simulate an anthropogenic climate change and contribute the AR4 (the 4-th Assessment Report of IPCC). This project is called as K-1 (K stands for the first letter of “Kyousei”). In this model, no flux correction is applied. The globally averaged surface temperature simulated by this model is shown in Fig. 13-3. It is concluded that there is no climate drift (Sumi et al., 2003). For more detailed information, please refer to the hope page (www.renjyu.net/kyousei/). At the same time, a research to simulate the surface temperature change of the 20 century is being conducted at NIES. Various forcing parameters during the 20 century including is prepared and will be distributed by NIES.

Another project is being done with CRIEP (Central Research Institute of Electronic Power) .NCAR (National Center for Atmospheric Research) and LLNL (Laurence Livermore National Laboratory), where the ensemble simulation of global warming will be done by using the medium resolution of NCAR CCSM3.0.

The integrated Earth System model is being developed mainly in FRSGC. SPRINTERS (Spectral Radiation-Transport Model for Aerosol Species, refer to http://cfors.riam.kyushu-u.ac.jp/~toshi/indexj.html),which is the aerosol transport model developed at CCSR (Takemura et al., 2003) , the stratospheric chemistry model and CHASER (Chemical AGCM for Study of Atmospheric Environment and Radiative Forcing, refer to

55

http://ccsr.u-tokyo.ac.jp/~kengo/study/chaser.html), which is the troposphere atmospheric chemistry model (Sudo et al,2002) are being integrated into the CCSR/NIES medium resolution climate model. Carbon cycle model in the ocean is being developed and will be plugged in the climate model. A dynamic vegetation model and a carbon cycle model over the land (Sim-CYCLE) are being developed. Simulation of carbon cycle in the Earth System is a final goal of this research.

High resolution of Numerical Prediction Model is being developed at JMA (Japan Meteorological Agency). TL1053 (20km) L40 NWP model is being tested. Fig. 13-4 shows the IR cloud pictures computed by this model result with the observed GMS IR picture. Comparison is quite good. MRI (Meteorological Research Institute) will use this model in the time-slice experiment for the Global Warming. Much more detailed information is expected to be given, although there remain many issues, especially how to handle a parameterization scheme for convection is a critical issue. 13.3. Other model development

Besides the research relating to the global warming issue, many research efforts are being done to understand atmospheric and oceanic variability. For example, AFES (Atmospheric model For the Earth Simulator) and OFES (Ocean model for Earth Simulator) is being developed and the coupled model (SINTEX-F1.0:T106L19 ECHAM4.0+2 x 1.5-0.5 OPA8.2) for the interannual variability is being developed at FRSGC through EU-Japan collaboration.

4-dimensional variational method by using an atmosphere-ocean coupled model is being developed by FRSGC and Kyoto University group.

Fig. 13-3. Globally averaged surface temperature due to the high resolution climate model.

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Fig. 13-4. (Left) IR image by the TL11023 model, and (right) observed IR image by GMS-5.

References

Sumi, A., M. Kimoto, S. Emori, M. Nozawa, H. Kanzawa and H. Hasumi (2003): Model development for the Global warming prediction by using the Earth Simulator. Proceedings of the International Symposium on Climate Change (ISCC), WMO/TD-No.1172, 76-79.

Takemura, T., T. Nakajima, A. Higurashi, S. Ohta and N. Sugimoto (2003): Aerosol distributions and radiative forcing over the Asia-Pacific region simulated by Spectral Radiation-Transport Model for Aerosol Species (SPRINTARS). J. Geophys. Res., 108, ACE 27 1-9.

Sudo, K., M. Takahashi, J. Kurokawa and H. Akimoto (2002): CHASER: A global chemical model of the troposphere 1.Model description. J. Geophys. Res., 107.

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Annex 1

Japanese Committee for CLIVAR

Japanese Committee for CLIVAR was established as the corresponding body to the International CLIVAR activities, under the Japanese Committee for WCRP, Science Council of Japan. Membership is as follows.

Name Affiliation Remarks (International committee)

Shigaru Aoki (ILTS/Hokkaido Univ.) CLIVAR-SOIP Toshiyuki Awaji (Kyoto Univ.) Yoshifumi Kuroda (JAMSTEC) CLIVAR/GOOS-IOP, TIP Toshio Suga* (Tohoku Univ.) Masato Sugi (JMA) CLIVAR-WGSIP Yasushi Takatsuki (JMA) Kensuke Takeuchi (FORSGC) Argo-ST Akira Noda (MRI/JMA) JSC/CLIVAR-WGCM Hiroyasu Hasumi (CCSR/Univ. Tokyo) CLIVAR/WGCM-WGOMD Yukio Masumoto (Univ. Tokyo) CLIVAR/GOOS-IOP Yutaka Michida (ORI/Univ. Tokyo) OOPC Humio Mitsudera (ILTS/Hokkaido Univ.) Shoshiro Minobe (Hokkaido Univ.) Tatsushi Tokioka ** (FRSGC) CLIVAR-SSG Ichiro Yasuda (Univ. Tokyo) Tetsuzo Yasunari (HyARC/Nagoya Univ.) JSC Hiroyuki Yoritaka (JCG) Tomowo Watanabe (NRIFS) *Chairperson **Vice-chairperson Main activity items are as follows. (1) To collect and circulate information on CLIVAR project and other related programs such as

GEWEX, GODAE, Argo, GCOS and GOOS. (2) To discuss and coordinate possible contributions of Japanese community to international

CLIVAR project.

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Annex 2

Recent Progress in Physical Oceanography in Japan*

*Reproduced from “Report of Oceanographic Studies in Japan for the Period from 1999 to 2002” prepared for submission to IAPSO at its XXIII General Assembly in Sapporo, Japan, June-July 2003 by Japan National Committee for the Physical Science of the Ocean, Science Council of Japan.

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Remark On October 4, 2002 during the Fall Meeting of the Oceanographic Society of Japan (JOS), the Japan

National Committee for the Physical Sciences of the Ocean, Science Council of Japan (SCJ), has sponsored the symposium entitled “Recent Progress in Physical Oceanography in Japan”, as one of sessions of the symposium of “Our Oceanography toward the World Oceanography”, SCOR-JOS International Symposium (See the program below).

In this symposium, there were nine presentations including one by the invited speaker from foreign

country. Before the symposium, the committee asked eight Japanese presenters to review a recent progress achieved by Japanese scientists. In order to effectively conduct this task, the committee also advised them to establish a review team consisting of several potential scientists in each field, and to properly prepare the presentation materials.

Since the committee judged all presentations were properly accomplished, the abstracts prepared by the

eight Japanese presenters were cited as Part 1 of the report. (Kimio Hanawa, Tohoku University)

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Our Oceanography toward the World Oceanography Physical Oceanography – Session A

4 October 2002 Hokkaido University

Recent Progress in Physical Oceanography in Japan

Conveners:

Kimio HANAWA (Graduate School of Science, Tohoku University) Toshio YAMAGATA (Graduate School of Science, University of Tokyo) Shiro IMAWAKI (Research Institute for Applied Mechanics, Kyushu University)

Program 13:30-13:35 Introduction

Dr. Kimio HANAWA (Tohoku University) 13:35-14:05 Combining data and coupled atmosphere-ocean models:

an application to the Adriatic Sea Dr. Roberto PURINI (C.N.R., Italy: Invited speaker)

14:05-14:30 Research on the Kuroshio Dr. Kaoru ICHIKAWA (Kyushu University)

14:30-14:55 Recent Japanese contributions in hydrography to understanding of the three-dimensional oceanic structure and circulation

Dr. Toshio SUGA (Tohoku University) 14:55-15:20 Decadal variability and large-scale air-sea interaction

Dr. Shoshiro MINOBE (Hokkaido University) (15:20-15:40 Coffee break)

15:40-16:05 Satellite oceanography in Japan Dr. Masahisa KUBOTA (Tokai University)

16:05-16:30 Numerical modeling of open ocean circulation Dr. Hiroshi ISHIZAKI (Meteorological Research Institute)

16:30-16:55 Research on the Japan Sea and adjacent areas Dr. Jong-Hwan YOON (Kyushu University)

16:55-17:20 Research on the Sea of Okhotsk and adjacent areas Dr. Kai I. OHSHIMA (Hokkaido University)

17:20-17:45 Cooperative studies with Asian countries Dr. Tetsuo YANAGI (Kyushu University)

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I. Research on the Kuroshio

Kaoru ICHIKAWA (Kyushu University)

Introduction

The Kuroshio is obviously one of the major targets of Japanese oceanographers, due to its important roles in global climate changes and also its huge impacts on the local Japanese coastal areas. Plenty of researches on the Kuroshio have been conducted from various viewpoints, including in situ and/or satellite observations, numerical simulation and assimilation, and theoretical approaches. Summarizing all those researches is indubitably far beyond this short review, so that only the research tendencies in this decade are introduced with a few substantial examples.

Kuroshio volume transport

Variations of volume transport of the Kuroshio, together with current path and velocity, have been clarified using sea level records from tide gauges and ship data of the Japanese agencies, examining their relations to the large meander (Fig. 1). These relations are also evaluated by some simplified numerical experiments.

Quantitative direct measurements of the Kuroshio volume transport are established by so-called ASUKA-line observations, or extensive hydrographic observations and long-term dense moorings along the TOPEX/POSEIDON subtrack off the Cape Ashizuri (Fig. 1). Combining these data, the northeastward volume transport in the upper 1000m layer and the net Kuroshio transport, which accounts the westward recirculation flow south of the Kuroshio, are estimated (Fig. 2).

On the contrary to the classic Sverdrup theory, they show no significant seasonal variations. The fluctuations in Fig. 2 are eventually revealed by satellite altimetry to be related with interactions with off-shore meso-scale eddies.

The mean net volume transport across the ASUKA line is larger than that estimated in East China Sea, suggesting existence of the Ryukyu current system, a northeastward flow east of the Ryukyu Islands merging into the Kuroshio. In addition, the quantitative estimation of the net volume transport provides good reference for recent high-resolution numerical models. Acknowledgement

This review is conducted by a review team (Drs. K. Akitomo, T. Hibiya, H. Ichikawa, K. Ichikawa, S. Imawaki, M. Kawabe, and T. Yamagata; in alphabetical order).

Cape Ashizuri

Honshu

Kyushu

Shikoku

Toka

ra S

trait

Ryuky

u Isla

nds

PN line ASUKA line

TOLEX line

Kii Pen.

125E 130E 135E 140E120E

35N

30N

25N

Fig. 1. Schematic Kuroshio path and geographical names in the adjacent (based on Kawabe, 1995). Broken lines south of Shikoku and Honshu islands indicate bimodal structure of the Kuroshio path. In the figure, observational lines (PN, ASUKA, and TOLEX) are also shown by straight lines.. A dotted line east of the Ryukyu Islands indicates possible Ryukyu current system.

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20

40

60

80

100

Tra

nspo

rt (

Sv)

1993 1994 1995 1996 1997 1998 1999 2000 2001

20

40

60

80

100

Tra

nspo

rt (

Sv)

1993 1994 1995 1996 1997 1998 1999 2000 2001

Fig. 2. Northeastward volume transport across the ASUKA line (a), and the net volume transport north of 26N (b). After Imawaki et al. (2001). ****************************************************************************************

II. Recent Japanese Contributions in Hydrography to Understanding of the Three-dimensional Oceanic Structure and Circulation

Toshio SUGA1, Masao FUKASAWA2, Masaki KAWABE3, and Ichiro YASUDA3

1: Tohoku University, 2: Japan Marine Science and Technology Center, 3: University of Tokyo

Understanding of the three-dimensional hydrographic structure and circulation of the world ocean based on observational data has been greatly progressed during the last decade owing to the World Ocean Circulation Experiment (WOCE) and other research projects. Japanese researchers have actively participated in these endeavors especially for the North Pacific, such as the WOCE Hydrographic Programme (WHP) P2, P8, P9, P13, P24, etc. Some of the major contributions are summarized in the present review.

Both detailed analyses of historical data and intensive surveys including the WHP sections have enriched our knowledge about the near-surface oceanic structure and circulation. Several new features of the dominant waters in the subtropical permanent pycnocline were revealed. The formation and circulation of North Pacific Tropical Water and North Pacific Subtropical Mode Water were described in detail along with their temporal variability. North Pacific Central Mode Water was found and defined, and its importance in the decadal variability of the North Pacific was demonstrated. Near-surface features in the subarctic region have also been better understood. The subsurface temperature minimum and maximum, which are essential structures of the subarctic North Pacific and frequently called dichothermal water and mesothermal water, were reexamined and their spatial distribution and formation processes were put in new perspective such as air-sea interaction, inter-gyre exchange, etc.

The formation process of North Pacific Intermediate Water (NPIW) had been one of the major questions among the oceanographic community for more than half century. Elaborate analyses of the historical data and succeeding intensive surveys especially in the mixed water region between the Kuroshio Extension and the Oyashio revealed it to such extent that the formation rate of NPIW is now discussed quantitatively. The progress in understanding of NPIW is definitely one of the major Japanese accomplishments in the oceanography for the last decade.

The deep circulation in the North Pacific had been least known in the world ocean. The abyssal water

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and its circulation in the North Pacific have been described through the WHP and other surveys of the comparable quality as WHP observation. In particular, the bifurcation of the deep current just north of the Samoan Passage was confirmed, and the flow routes and structure of the eastern (deeper) and western (shallower) branch currents, carrying the Lower Circumpolar Water, were clarified. The WHP P1 in the northern North Pacific has been revisited as part of the research project participated by many Japanese agencies and universities called Subarctic Gyre Experiment (SAGE), which revealed significant changes in properties of the deep and bottom waters, encouraging further Japanese commitment in deep hydrography in future. ****************************************************************************************

III. Decadal Variability and Large-scale Air-sea Interaction

Shoshiro MINOBE1, Toshio SUGA2, Tomowo WATANABE3, Youichi TANIMOTO1, and Kimio HANAWA2

1: Hokkaido University, 2: Tohoku University, 3: Tohoku National Fisheries Research Institute

Climate variability and its predictability have attracted large attentions, as shown by the fact that this field is one of three major components of CLIVAR program. Subtle but meaningful differences of the spatial structure of decadal variability from that of the interannual variability (Tanimoto et al., 1993 JCLM; 1997 JMSJ) indicates that the decadal variability is worth to be examined by its own right. Researchers in Japan have also been working on this exciting topic. In this presentation, we summarize major contributions of Japanese studies in the last decade, and illustrate main topics in Fig. 1.

For the Pacific Ocean, one of the most prominent features of the decadal variability is climatic regime shifts. It is widely accepted that the major regime shifts occurred in the 1920s, 1940s and 1970s (Minobe, 1997 GRL) and some other climatic transitions or shifts were detected (Yasunaka and Hanawa, 2002). These variabilities are likely to be closely associated with the 20-yr and 50-70-yr oscillations of the Aleutian lows (Minobe, 1999 GRL; 2000 PiO), which were inferred to be a main body of the Pacific Decadal Oscillation (PDO) (see Mantua and Hare, 2002 JO for a recent review of the PDO). The influences of 20-yr oscillation are also observed in Japanese coastal sea-level displacements (Senjyu et al., 1999 JO) and precipitations over the Pacific Ocean (Minobe and Nakanowatari, 2002 GRL). Although there is no widely accepted agreement for the PDO mechanism, Luo and Yamagata (2001 JGR) provided an interesting hypothesis that the interaction between the equatorial region and southern hemisphere forms a delayed oscillator on a 10-20 yr timescale．A recent change occurred in 1998/99 over the North Pacific is now debated whether it is a major climatic regime shift and new regime lasting in another 20-30 years (e.g., Minobe, 2002 PiO in press).

Influences of regime shifts or decadal variability of the Aleutian low are widely found over the North

Pacific. A stronger Aleutian low induces enhanced Kuroshio transport (Yasuda and Hanawa, 1997), and brought anomalous southward intrusions of Oyashio (Hanawa, 1995 BHNFRI; Minobe 1997, GRL; Sekine 1999 PiO). Regime shifts also strongly influenced properties and formation amounts of major water masses as observed in the Subtropical Mode Water (STMW, Yasuda and Hanawa 1997; Hanawa and Kamada, 2001 GRL), the Tropical Water (Suga et al., 2000 PiO), and the Central Mode Water (Suga et al., JO submitted). How the atmospheric forcings influence to the water properties and circulations have been investigated using numerical models (Inui et al., 1999 JPO; Nonaka et al., 2000 GRL; 2002 GRL; Xie et al., 2000 JPO) and observational analyses (Yasuda et al., 2000).

For the Atlantic Ocean, Xie and Tanimoto (1998 GRL) and Tanimoto and Xie (1999 JMSJ) proposed a concept of pan-Atlantic decadal oscillation, which involves a cross-equatorial SST gradient or a SST dipole and the North Atlantic Oscillation (NAO). The tropical dipole in the Atlantic was identified as a weakly damped mode of the atmosphere-ocean system (Xie et al., 1999 GRL; Xie, 1999 JCLI), and interacts with the NAO (Okumura et al., GRL 2001). On the other hand, the predominant decadal variability of the Arctic Oscillation (AO)/NAO in the last forty years was hypothesized to be a self sustained mode in the Arctic Sea and the adjacent atmosphere under a recent condition due to the global warming in the 20th century (Ikeda et al., 2001 GRL). The decadal AO/NAO influenced the northwestern Pacific (Xie et al., 1999 JMSJ), and dominated decadal variability of the western Pacific marginal seas such as the Japan Sea (Minobe et al., JPO submitted).

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Fig. 1. Some topics that will be presented.

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IV. Satellite Oceanography in Japan

Masahisa KUBOTA1, Kaoru ICHIKAWA2, Shiro IMAWAKI2, Joji ISHIZAKA3, Naoto EBUCHI4, Hiroshi KAWAMURA5, Kunio KUTSUWADA1, and Toshiro SAINO6

1: Tokai University, 2: Kyusyu University, 3: Nagasaki University, 4: Hokkaido University, 5: Tohoku University, 6: Nagoya University

1. Ocean Color

Data from Coastal Zone Color Scanner (CZCS) were used for applications around Japan, and it was shown that satellite ocean color data were useful for oceanography and fisheries. National Space Development Agency of Japan (NASDA) launched Advanced Earth Observation Satellite (ADEOS) on 1996, and one of the core sensors was Ocean Color and Temperature Scanner (OCTS). Ocean color and temperature data simultaneously obtained by the OCTS were applied to various aspects of oceanography. This is well demonstrated in the special volume of Journal of Oceanography on the ADEOS field campaign off Sanriku, Japan. With termination of OCTS operation, those studies were continued taking advantage of the SeaWiFS data. ADEOS-II will be launched on November 2003, and Global Imager (GLI) will be on-board. 2. Altimeter

Since those Japanese altimetry data sets are required to include the Kuroshio, the temporal mean sea surface dynamic topography (SSDT) must be well defined. Simultaneous use of in situ hydrographic observations and/or surface drifter data with the altimetry data has been adopted to obtain the mean SSDT field. These data sets have allowed us to study extensively interactions between meso-scale eddies and the Kuroshio or Kuroshio Extension. 3. Marine Surface Wind

In 1990’s and 2000’s, several missions, which carry, microwave scatterometer to observe marine surface vector winds have been launched and are planed to be launched. Under these circumstances, several studies to evaluate the observed wind data comparing with ocean buoy data have been executed in Japan with international collaborations (e.g., Ebuchi et al., 1998, 2002). Ebuchi and Graber (1998). Ebuchi (1997, 1999a, b, 2000) developed a new technique to assess self-consistency of the scatterometer-derived wind directions.

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Kubota and Yokota (1998) and Kutsuwada (1998) composed gridded vector wind fields from the scatterometer observations. 4. Sea Surface Temperature

We have established a development team formed by relating Japanese agencies, and generated a new SST product by merging AVHRR, GMS and TRMM SSTs. Using the hourly GMS solar radiation and the surface winds from SeaWinds, SSMI and TRMM, diurnal effects are eliminated to adjust all SSTs acquired at different times in a day to the daily minimum SSTs at around 1m depth. Then, all SSTs are merged using an objective analysis for one year, October 1999–September 2000. The new generation SST has following features better than the previous SST products, 1) cloud-free, 2) daily and 3) high-spatial resolution. 5. Latent Heat Flux

Kubota et al. (2002b) constructed global latent heat flux data set based on satellite data and clarified the characteristics of the data set by comparing with other data sets including not only satellite-derived but also reanalysis data such as ERA15 and NRA1 6. Japanese Ocean Flux data sets with Use of Remote sensing Observations (J-OFURO)

Various satellite data products such as shortwave radiation, longwave radiation, latent heat flux, sensible heat flux, ocean surface wind speed and sea surface dynamic topography are provided on the J-OFURO Web site (http://dtsv.scc.u-tokai.ac.jp). The data set is called as Japanese Ocean Flux data sets with Use of Remote sensing Observations (J-OFURO). The description for J-OFURO is given in Kubota et al. (2002a). ****************************************************************************************

V. Numerical Modeling of Open Ocean Circulation

Hiroshi ISHIZAKI1, Masahiro ENDOH2, Hiroyasu HASUMI2, Yasuhiro YAMANAKA3, Michio KISHI3, Toshio YAMAGATA2, Masafumi KAMACHI1, Toshiyuki AWAJI4,

and Motoyoshi IKEDA3 1: Meteorological Research Institute, 2: University of Tokyo, 3: Hokkaido University,

4: Kyoto University

1. Introduction Following the development of super computers, modeling studies on the ocean general circulation with

associated physical processes have been developing in quality and quantity, in particular, in the simulation fields. These dynamical ocean models are used not only in the stand-alone simulations but also in the complex modeling such as ocean-atmosphere coupling models, ocean data assimilation, geochemical and ecosystem models and so forth. Here, we briefly review the activities in those fields associated with the open ocean circulation. 2. Japanese activities 1) Tropical circulation

Studies on the following subjects have been advanced in terms of modeling at University of Tokyo: the bifurcation of the North Equatorial Current, variations of the Mindanao Current and the Mindanao Dome, the intra-seasonal oscillation due to eddies in the Indonesian Seas, the variation of the Indonesian Throughflow, the forced oceanic waves in the Indian Ocean, and so forth. It is also pointed out that understanding on the air-sea interaction in the Indian Ocean was promoted. 2) Mid-latitude circulation

Developing high-resolution models of subtropical gyre including the Kuroshio and the marginal seas, a prediction system for the oceanic conditions is about to be put to practical use at University of Tokyo. The importance of the mesoscale eddies and bottom topography on the prediction on ocean current variability has been recognized. The relationship has been made clear between these regional variabilities and the basin-scale climate variabilities such as El Nino.

Decadal variability of the upper thermal structure in the North Pacific has been investigated at Meteorological Research Institute (MRI), focusing on the subduction process and the North Pacific

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Subtropical Mode Water (NPSTMW). Long-term variations in the divergence of the heat transport in the Ekman layer are important for the former, and those in the heat advection by the Kuroshio Extension in response to the spin-up/down of the subtropical gyre for the latter.

High-resolution (eddy-permitting) models of the North Pacific have been also developed at MRI and used for simulations of the climatological thermal structure in the surface layer, the bimodality of the Kuroshio flow path south of Japan, and the formation process of the North Pacific Intermediate Water (NPIW). The climatological features in the surface layer are well simulated by the model. The Kuroshio transport clearly affects the flow path south of Japan, as has been shown by simple models. Small-scale disturbances are crucial to mix the Oyashio and Kuroshio Waters to form the NPIW. 3) High-latitude and polar regions

The sea-ice modeling is the most important factor in these regions. Development and improvement in sea-ice models have been made at Hokkaido University, including the modeling of the mixed layer beneath the sea ice. Two-dimensional and three-dimensional modeling of the deep convection associated with the deep and bottom waters have been made at Kyoto University. 4) Large-scale thermohaline circulation

At Center for Climate System Research (CCSR), World Ocean modeling has been conducted with an emphasis on the thermohaline circulation. They have developed their own OGCM, with a new bottom boundary layer parameterization and a number of high-precision numerical algorithms implemented to better reproduce the global thermohaline circulation. The focus of modeling is on the control of the global-scale thermohaline circulation by winds and vertical diffusivity. The Atlantic deep circulation is shown to be controlled by wind-enhanced buoyancy gain of NADW and be relatively insensitive to vertical diffusivity, while the Pacific deep circulation is shown to be very sensitive to vertical diffusivity, especially to its values at lower thermocline depths. Horizontal variations in vertical diffusivity could also significantly affect the Pacific deep circulation. A sea ice model is also developed at CCSR, and its effect on deep water masses and circulation is investigated by use of a global ice-ocean coupled GCM. 5) Ocean-atmosphere coupling model

The coupled atmosphere-ocean general circulation model (CGCM) has been developed at MRI for various climate studies. The CGCM reveals reasonable natural climate variability, in particular, the interannual and interdecadal Pacific variability as well as the realistic overall mean climate. Results of a series of global warming experiments have contributed to IPCC (2001). A set of hindcast simulations made with the CGCM succeeded in reasonably reproducing historical climate change since the pre-industrial revolution. A contribution to IPCC has been also made by CCSR based on their CGCM experiment. 6) Ocean data assimilation

By using a free-surface ocean general circulation model and the variational adjoint method, a global ocean data assimilation system has been conducted at Kyoto University, capable of providing a comprehensive 4-dimensional dataset. The system, applied to an experiment to define the climatological seasonal state of the global ocean, showed its efficiency in reproducing the observed features, such as the low salinity NPIW, and high-accuracy heat and freshwater fluxes better than those obtained by the flux correction method in a CGCM.

At MRI, an ocean data assimilation system (COMPASS-K) has been developed with purposes of understanding ocean variability in the western North Pacific as a local response to a global climate change and nowcasting and forecasting of ocean states. The system is operationally used in JMA. Another ocean data assimilation system (ODAS) has been operated in JMA to provide initial conditions for prediction with a CGCM.

Other ocean data assimilation systems have been developed and used for various research studies at the Frontier Group, JAMSTEC, Kyushu University, Hokkaidou University, and Tokai University. All of the assimilation studies in Japan contribute to the GODAE project. 7) Biogeochemical and ecosystem models

Simulations of the CFC and anthropogenic carbon dioxide concentrations in the ocean have been made as a part of the North Pacific Carbon Cycle Study (NOPACCS) in the former NIRE. A three-dimensional

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biogeochemical model has been also developed at CCSR, treating organic carbon. Recently, similar models have been developed in MRI, CRIEPI, and Hokkaido University.

The lower trophic level models mainly deals with HNLC (High Nutrient Low Chrolophyll) condition of north eastern Pacific and spring bloom of north western Pacific (Hokkaido University). A future research direction should be to sort out priorities of various biological and chemical processes with the long-term variation problem being the axis, while keeping the model complexity at a minimum and invoking the parameter optimization technique. ****************************************************************************************

VI. Research on the Japan Sea and Adjacent Areas

Jong-Hwan YOON, Atsuhiko ISOBE, and Tomoharu Senjyu (Kyushu University)

A salient feature of the researches on the Japan, Yellow and East China Sea is that recently introduced

instruments and facilities have been widely utilized in various surveys. The estimation of tidal harmonic constants in these seas using aliasing period of each tidal component against satellite track period from the mid 90’s allowed the study of the seasonal and inter-annual variations of the surface current system in these seas. Over 30 PALACE floats have been deployed into the Japan Sea providing a great amount of profiles of temperature and salinity for upper 800 m. Twenty-five IES mounted at the bottom in the Tsushima Basin provided two year’s time series of vertical stratifications. The ADCP mounted to a regular ferry boat “Camellia” between Hakata and Pusan has been monitoring the Tsushima Current structure across the Straits 6 times a week since 1997 and obtained about 2.6 Sv as mean volume transport of the Tsushima Current. At the end of 2000, HF radar system has been established at the Tsushima Island and adjacent areas to monitor the surface current at the Tsushima Straits.

International corporations have been activated. Comprehensive surveys by CREAMS-I, II (1993-1997, 1998-2002) have been conducted since 1993. NEAR-GOOS, a regional program of WOCE, is now providing real time database of ocean and atmosphere in both seas under the corporation between countries surrounding these seas. International symposiums have been held annually or biannually by CREAMS and JECSS-PAMS. 1. Japan Sea

The international program clarified many interesting aspects of the northern part of the Japan Sea, which have been masked by “the iron curtain” during the Cold War.

The existence of a large cyclonic circulation in upper 1000 m was confirmed north of 40oN and east of 132oE in the Japan Basin by hydrographic surveys and PALACE float experiments. The low salinity water along the Russian coast originating from the Amur River feeds the subsurface low salinity core along the Subpolar Front corresponding to the southern boundary of the circulation as well as the subsurface salinity minimum (Japan Sea intermediate water) in the Tsushima Warm Water region. ARGOS buoys tracks suggest additional wind driven gyres such as a cyclonic gyre northwest of Hokkaido as well as an anticyclonic gyre in winter west of the large cyclonic gyre mentioned above.

Long term deep current measurements reveal that a strong anti-cyclonic circulation (about 5 cm/s) follows the slope region of the deep basins, whereas strong variabilities exceeding 30cm/s episodically are dominant in the central flat area of the deep basin.

Monotonic increase of temperature and decrease of dissolved oxygen in deep layer during past half century suggest the stop or almost stop of the deep water formation and associated overturning with one hundred years time scale suggesting the Japan Sea as “a litmus paper” for global warming. While, the formation of intermediate waters is still active in the northern part of the Japan Sea possibly near Vladivostok.

In contradiction to the warming trend, the deep water formation was successfully observed off Vladivostok in 2000-2001 winter, which is a coldest winter among recent years.

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2. East China Sea and Yellow Sea

An international project (Marginal Sea Flux Experiment in the West Pacific) between Japan and China from 1992 to 1996 provided many new findings about the transport processes of dissolved and suspended materials from China continent to the Kuroshio, and CO2 absorption rate of the East China Sea.

A recent study suggests the origin of the Tsushima Warm Current moves seasonally. The Tsushima Warm Current originates near Taiwan except autumn, however, in autumn, it bifurcates from the Kuroshio southwest of Kyushu.

Long term drifter buoy surveys and CTD measurements provided detailed structures of behavior of the low salinity water plume from the Yangtze River, which supplies fresh water into the Japan Sea. Current measurements with 7 IES for 14 months to survey the frontal wave characteristics along the Kuroshio in the East China Sea revealed that dominant periods are 7, 11 and 16 days, and phase speeds are 17, 20, 28 km day-1. ****************************************************************************************

VII. Research on the Sea of Okhotsk and Adjacent Areas

Kay I. OHSHIMA (Hokkaido University)

The Okhotsk Sea is the southernmost seasonal ice zone in the Northern Hemisphere with large

interannual variations of sea ice extent, and thus it can be considered as a sensitive indicator of climate change. North Pacific Intermediate Water (NPIW) is ventilated mainly in and around the Okhotsk Sea. In other words, the Okhotsk Sea can be regarded as the only site that the atmosphere can directly exchange the heat and material (including CO2) with the intermediate water in the North Pacific. Despite the recent realization of the importance of the Okhotsk Sea, in-situ observations had been very limited before 1990's because of the political issue and severe winter conditions.

After 1990's, the situation has changed and some international projects have been carried out to clarify this 'sealed sea'. The largest project is the Joint Japanese-Russian-U.S. Study of the Sea of Okhotsk, with R/V Khromov during 1998-2001, mainly sponsored by CREST, Japan Science and Technology Corporation. The main participants are Hokkaido University (P.I. M.Wakatsuchi), JAMSTEC (P.I. T. Takizawa), FERHRI (P.I. Y. Volkov), S. Riser, L. Talley, and D. Rudnick.

The surface drifters and profiling floats clearly revealed the existence of the southward boundary current off Sakhalin (East Sakhalin Current: ESC). A part of the ESC continues as far as the southern tip of Sakhalin Island while another part turns to the east 48-51N, suggesting the cyclonic circulation (Ohshima et al., 2002 JGR). The long-term mooring measurements clarified the structure of the ESC and its seasonal variation (Mizuta et al., 2003 JPO). The volume transport of this current at 53N is estimated to be 6.7 Sv in annual average, with maximum of 12.3 Sv in February. The main flow exists in the shelf slope, extending from the surface to the bottom. It is proposed that the cyclonic circulation is driven by the wind stress curl and that a part of the ESC can be regarded as its western boundary current. On the other hand, in the southern Kuril Basin, the existence of anticyclonic circulation with several (anticyclonic) mesoscale eddies have been shown from hydrographic data, satellite images (Wakatsuchi and Martin, 1990 JGR), surface drifters and profiling floats.

In the northwest shelf, water with nearly freezing point at density up to 27.1 sigma-theta is formed due to active sea ice formation in the polynya (Kitani, 1973). This water, called Dense Shelf Water, is believed to be the main ventilation source in the Okhotsk Sea and accordingly North Pacific. The new hydrographic observations and the current moorings have shown that Dense Shelf Water flows southward as a bottom-intensified current (Mizuta et al., 2003 JPO). This Dense Shelf Water mixes with Western Subarctic Water originating from the Pacific to form the Okhotsk Sea Intermediate Water (OSIW). OSIW is an important ingredient of NPIW (Yasuda, 1997 JGR; Watanabe and Wakatsuchi, 1998 JGR). The mixing ratio and the annual production rate of OSIW have been estimated from historical hydrographic data (Itoh et al.,

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2003 JGR), and CFC and oxygen isotope data (Yamamoto et al., 2002 DSR). CFC and the isotope data also suggest the importance of vertical mixing in and around the Kuril Straits on the water mass formation and the ventilation.

Recent intensive LADCP and CTD observations have revealed a two-layer structure of the mean flow across the Bussol Strait, the largest strait in the Kuril Islands, where the upper layer flows out of the Okhotsk and the lower layer in the opposite direction (Katsumata et al., 2003). By integrating in the cross section, the transport through the Strait is 9 Sv outflow from the Okhotsk. It is also demonstrated that the tidal amplitude reaches more than 1 m/s even in the depth greater than 1000m. Acknowledgements

This review is conducted by a review team (Drs. Y. Fukamachi, T. Kono, G. Mizuta, M. Wakatsuchi, and I. Yasuda; in alphabetical order). ****************************************************************************************

VIII. Cooperative Studies with Asian Countries

Tetsuo YANAGI (Kyushu University)

JSPS (Japan Society for Promoting Sciences) Multilateral Cooperative Research Program - Coastal

Oceanography - has started in 2001 and will continue until 2010. The participating countries for this project are Japan, Philippines, Vietnam, Thailand, Malaysia and Indonesia. This program consists of four core projects: 1. "Water circulation and the process of material transport in the coastal area and marginal seas of the East

and Southeast Asia" (P.I.: T. Yanagi) 2. "Ecology and oceanography of harmful marine microalgae" (P.I.: Y. Fukuyo) 3. "Biodiversity studies in the coastal waters of the East and Southeast Asia" (P.I.: M. Terazaki) 4. "Pollution of hazardous chemicals in the coastal marine environment and their ecological effect" (P.I.: N.

Miyazaki).

The aims of core project 1 are 1) to establish the analysis method of satellite images (NOAA, SeaWiFS and Topex/Poseidon) in the East and Southeast Asia, 2) to develop a numerical hydrodynamic model applicable to the East and Southeast Asia and 3) to develop a numerical ecosystem model applicable to the east and Southeast Asia, for the successful coastal zone management.