Leaving a Legacy The VAMOS Ocean-Cloud- Orobwood/VOCALS/papers/VariationsV5N1.pdf · mulus deck in...

us CLIVARU.S. CLIVAR

U.S. CLIMATE VARIABILITY AND PREDICTABILITY (CLIVAR)1717 Pennsylvania Avenue, NW, Suite 250, Washington, DC 20006• www.usclivar.org

VOCALS is one of the princi-pal activities of theW C R P / C L I VAR VA M O Spanel, and has links with the

GEWEX Cloud System Study (GCSS)group. The Southeast Pacific (SEP) cli-mate is a tightly coupled system involv-ing poorly understood interactionsbetween clouds, aerosols, marine bound-ary layer (MBL) processes, upper oceandynamics and thermodynamics, coastalcurrents and upwelling, large-scale subsi-dence, and regional diurnal circulations(Fig. 1). This unique system is verysparsely observed, yet its variations haveimportant impacts on the global climate.There are also great economic impacts,with the regional fisheries representingalmost one-fifth of the worldwide marinefish catch.

The Andes Cordillera are barriers tozonal flow in the South Pacific, resultingin strong winds parallel to the coasts ofChile and Peru (Garreaud and Muñoz2005), which drive intense coastalupwelling, bringing cold, deep, nutri-ent/biota rich waters to the ocean surface.As a result, sea-surface temperatures(SSTs) are colder along the Chilean andPeruvian coasts than at any comparablelatitude. The cold SSTs, in combinationwith warm and dry air aloft helped byorographic effects of the Andes (Richterand Mechoso, 2006), support the largest

and most persistent subtropical stratocu-mulus deck in the world. The presence ofthis cloud deck has a major impact uponthe earth’s radiation budget.

Several fundamental problems arebarriers to the understanding of SEP’sweather and climate: These problemsinclude the serious difficulties in thequantification of the indirect effect ofaerosols upon cloud radiative properties(e.g. Lohmann and Feichter 2005). Also,coupled atmosphere-ocean general circu-lation models (CGCMs), have trouble-some systematic errors in the SEP,notably (Fig. 2) too warm SSTs and toolittle cloud cover (e.g. Mechoso et al.1995).

The principal program objectives ofVOCALS are: 1) the improved under-standing and regional/global model repre-sentation of aerosol indirect effects overthe SEP; 2) the elimination of systematicerrors in the region of coupled atmospher-ic-ocean general circulation models, andimproved model simulations and predic-tions of the coupled climate in the SEPand global impacts of the system variabil-ity. Program documents and informationcan be found at www.eol.ucar.edu/proj-ects/vocals/.The VOCALS Strategy

VOCALS is organized into two tight-ly coordinated components: 1) a RegionalExperiment (VOCALS-REx), and 2) a

Spring 2007, Vol. 5, No. 1

Leaving a Legacyby David M. Legler, Director

One the challenges of CLI-VAR is encouraging andguiding studies that not

only investigate processes impor-tant for the understanding andprediction of climate changes, butprovide a legacy that is more thana collection of dense observationsover a limited region and timeperiod. The North AmericanMonsoon Experiment, NAME,took place nearly 3 years agoand is now focusing on the syn-thesis of its results, its legacy ofimproved observational require-ments and improved forecastingcapabilities. As NAME windsdown, advance planning for anew study, VOCALS, is underway.VOCALS will explore the challeng-ing ocean-atmosphere dynamicsof the southeast Pacific and willconsider both the physical as wellas biogeochemical processes lead-ing to changes in cloud formationand upper ocean heat budgets inan attempt to improve coupledmodel simulations in this notori-ously difficult region. These arejust a few of the studies currentlyin place or in planning stages.Consult the U.S. CLIVAR webpages for information on otherstudies.

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VOCALS...................................................1U.S. CLIVAR Drought WG......................6North American Monsoon Prediction.......8C a l e n d a r...................................................10Global Ocean Energy Cycle ...................13Western Boundary Current WG..............16

IN THIS ISSUE

The VAMOS Ocean-Cloud-Atmosphere-Land Study (VOCALS)

Robert Wood, University of Washington; C. Roberto Mechoso, University ofCalifornia, Los Angeles; Christopher Bretherton, University of Washington; Barr

Huebert, University of Hawaii; Robert Weller, Woods Hole Oceanographic Institution

USCL.Spring2007 4/11/07 12:13 PM

U.S. CLIVARA little over a year ago U.S.

CLIVAR constituted some short-term Working Groups that wouldwork collaboratively on focusedand pressing scientific challengesand needs. The efforts of theseWorking Groups can be found onthe U.S. CLIVAR web site. TheOcean Salinity Working Group isfinishing their written findings andthe MJO Working Group effortswere highlighted at the recentWGNE Systematic Biases work-shop. Two other Working Groupswere recently initiated. Drought isa major focus of U.S. CLIVAR andthe Drought Working Group activ-ities (described in this article) willcomplement the DRICOMP fundedactivities, which were recentlysolicited. Please check the respec-tive Working Group web pagesfor further information and how toget involved.

The recently released USOcean Research Priorities Planand Implementation Strategy(http://ocean.ceq.gov/about/docs/orpp12607.pdf) includes, asone of its Near Term Priorities, theAtlantic Meridional OverturningCirculation (MOC). U.S. CLIVARand the agencies will be workingwith the community to developimplementation plans for this ini-tiative. More information will fol-low in the next Variations and onthe U.S. CLIVAR web site.

There are no in-situ observations of theseclouds with which to test hypotheses con-cerning their physics and chemistry.VOCALS observations will seek to quan-tify the controls on cloud condensationnuclei (CCN) formation and growth, inconcert with the IGBP’s Surface OceanLower Atmosphere Study, SOLAS.b. Systematic biases in atmosphere-oceanGCMs

CGCMs have difficulties in simulat-ing marine stratocumulus clouds (Ma etal. 1996; Kiehl and Gent 2004;Wittenberg et al. 2006). This is attributa-ble, in part, to the inadequate representa-tion of MBL processes (turbulence, driz-zle, mesoscale organization) in atmos-pheric models, and to a poor representa-tion of cloud microphysical processes(i.e. aerosol processes, including theirtransport from continental sources andtheir removal by drizzle). Studies usingCGCMs (Ma et al. 1996, Gordon et al.2000) demonstrate that the accurate pre-diction of the optical properties of lowclouds over the SEP is required in order tosimulate the strong trade winds and theobserved SST distribution.

The OGCM components of CGCMsalso have difficulties with coastalupwelling, and the offshore heat andnutrient transport by the associatedmesoscale eddy field (Penven et al. 2005,Colbo and Weller 2006).

Mean advection velocities in theupper ocean in the SEP are weak (few cms-1). The upper ocean, therefore accumu-lates and expresses locally the influences

VariationsPublished three times per yearU.S. CLIVAR Office1717 Pennsylvania Ave., NWSuite 250, Washington, DC 20006(202) [email protected]

Staff: Dr. David M. Legler, EditorCathy Stephens,Assistant Editor and Staff Writer

© 2007 U.S. CLIVAR Permission to use any scientific material (text and fig -ures) published in this Newsletter should be obtainedfrom the respective authors. Reference to newslettermaterials should appear as follows: AUTHORS, year.Title, U.S. CLIVAR Newsletter, No. pp. (unpublishedmanuscript).

This newsletter is supported through contributions tothe U.S. CLIVAR Office by NASA, NOAA—ClimateProgram Office, and NSF.

Continued from Page One

Modeling Program (VOCALS-Mod).Extended observations (e.g. IMET surfaceb u o y, satellites, cruises) will provideimportant additional contextual datasetsthat help to link the field and the modelingcomponents. The coordination throughVOCALS of observational and modelingefforts will accelerate the rate at whichfield data can be used to improve simula-tions and predictions of the tropical cli-mate variability. VOCALS is primarilysponsored by NSF and NOAA with con-tributions from the Office of NavalResearch (ONR), DOE, and internationalpartners.VOCALS Scientific Issuesa . A e rosol-cloud-drizzle interactions inthe marine PBL

In addition to responding to large-scale dynamics, cloud optical propertiesover the SEP are also impacted by atmos-pheric aerosols (Huneeus et al. 2006),with contributions from both natural andanthropogenic sources. Cloud dropleteffective radii are small off the coast ofChile and Peru, implying enhanced clouddroplet concentration, particularly down-wind of major copper smelters whosecombined sulfur emissions total 1.5 TgSyr-1, comparable to the entire sulfur emis-sions from large industrialized nationssuch as Mexico and Germany(Source:GEIA). Regional changes in sur-face and TOA radiation caused by theenhanced effective radii are as high as 10-20 W m-2, with significant, but currentlyunknown, implications for the ocean heatbudget.

Figure 1. Key features of the SEPclimate system.

The East Pacific Investigation ofClimate (EPIC) field study(Bretherton et al. 2004) found evi-dence that drizzle formation,enhanced by the depletion ofaerosols (Wood 2006) in the cleanMBL, can drive remarkably rapidtransitions which drastically reducecloud cover (Stevens et al. 2005).Although low clouds and the dynam-ical and microphysical processescontrolling their thickness and cover-age are a cornerstone of the climateof the SEP, our knowledge of cloudsin this region is so far limited to sur-face and spaceborne remote sensing.

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the characteristics of the sea surface tem-perature distribution across the SEP. Thehypotheses and testing strategies are pre-sented in full in the VOCALS ScientificProgram Overview (seewww.eol.ucar.edu/projects/vocals/).b. Aerosol-cloud-drizzle theme

A comprehensive suite of in-situ andremotely sensed cloud and boundarylayer measurements will be performedusing the aircraft platforms and the ships.Aircraft missions will focus upon under-standing the processes that control precip-itation, including the role of atmosphericaerosols, their transport from the land tothe ocean, and their depletion by theclouds themselves. A key goal is to betterlink aerosol microphysical variabilitywith the variability in the radiative prop-erties of the clouds by performing closurestudies that not only link cloud micro-physics with aerosol microphysics, butalso link the cloud optical properties(measured with aircraft and satelliteremote sensing) to the underlying aerosolvariability. SOLAS studies will seek torelate this aerosol variability to themarine sources and sinks of sulfur-con-taining gases and particles.c. Coupled ocean-atmosphere-land theme

of lateral fluxes associated with eddies(e.g. Penven et al. 2005), and verticalmixing events associated with atmos-pheric forcing transients (Wijesekeraand Gregg 1996). Mesoscale oceaneddies 50-200 km across can affectS S T well offshore by fluxing coldwater from the coastal upwellingregions (Fig. 3). Eddies could alsoimpact the ocean-atmosphere flux ofdimethylsulfide (DMS), an importantprecursor gas for cloud condensationnuclei. Eddy heat flux divergence mayaccount for roughly 40 W m-2 net heatflux into the ocean over the remote SEP(Colbo and Weller 2006). Mesoscaleeddies are poorly observed and under-stood, and are barely resolved in cou-pled ocean-atmosphere climate models(Canuto and Dubovikov 2005).Observations at the IMET buoy (20°S,85°W) show that another challenge forOGCMs is vertical mixing at the baseof the upper layer by near-inertial oscil-lations, which can entrain fluid fromthe cool, fresh intermediate waterbelow.

VOCALS-Mod posits that allevia-tion of the difficulties with the simula-tion of stratocumulus and coastalupwelling/ocean heat budget will resultin major improvements in GCM per-formance. These improvements includethe alleviation/elimination of the dou-ble-ITCZ biases that characterizes con-temporary CGCMs. There is evidencethat this bias has a negative effect onthe CGCM performance in the predic-tion of ENSO and its remote impacts.c. Interactions between the SEP withremote climates

There is consensus that climatevariability in the SEP can imprint a sig-nature in large-scale fields via telecon-

nections. Previous work has providedindications that features of tropical pre-cipitation patterns are strongly influ-enced by the SEP (Ma et al. 1996; Largeand Danabasoglu 2006). The pro-nounced annual cycle in the equatorialcold tongue is also considered to origi-nate from the SEP (Mitchell andWallace 1992). Atmospheric distur-bances in the SEP with an asymmetricstructure propagate westward in theform of Rossby waves (Xie 1996), andoceanic disturbances similarly propa-gate westward as Rossby waves andeddies (Chelton et al. 2006). However,the mechanisms of interaction are notwell understood.

Figure 3. SST and surface current variabilityassociated with the mesoscale ocean eddyfield in a regional ocean model.

4. VOCALS-RExa. Goals

VOCALS-Rex will collectdatasets required to address aset of issues that are organizedinto two broad themes: (1)aerosol-cloud-drizzle interac-tions in the marine boundarylayer (MBL) and the physico-chemical and spatiotemporalproperties of aerosols; (2)chemical and physical cou-plings between the upperocean, the land, and theatmosphere. The overarchinggoal for work in the firsttheme is a better understand-ing of processes that influencecloud optical properties (cloudcover, thickness, and particlesize) over the SEP. The goal ofthe second theme refers to theroles that oceanic upwelling,mesoscale eddies and othertransient upper oceanicprocesses play in determining

Figure 2. Annual mean sea-surface temperature biases inCCSM3 1990 control run (Collins et al. 2006)


U.S. CLIVAR

are used for climate change projectionand ENSO forecasting. VOCALS-Mod,therefore, provides the context forVOCALS and will directly benefit fromthe observations collected in the fieldcampaign. The principal objectives ofVOCALS-Mod are (1) improving theunderstanding and simulation of diurnal,seasonal, inter-annual, and inter-decadalvariability in the SEP; (2) improving theunderstanding and simulation of oceanicbudgets of heat, salinity, and nutrients inthe SEP and their feedbacks on theregional climate; (3) developing the capa-bility for simulation of cloud opticalproperties (coverage, thickness, anddroplet size) and the effect on these prop-erties of aerosols emitted in the region;(4) elucidating the interactions betweenthe SEP climate and remote climates.VOCALS-Mod will provide modelingsupport for VOCALS-REx through real-time forecasts and data assimilation. Theresearch methodology in VOCALS-Modwill be organized into several themes: • Downscaling to the V O C A L S - R e xstudy region: Global reanalysis data willbe used as forcings for RegionalAtmospheric Models (RAMs) andRegional Ocean Models (ROMs), theoutput of which will provide invaluableregional context in which to interpretVOCALS-REx field data. • Ocean mesoscale eddy structure andtransports: High resolution ROMs will beused in conjunction with the VOCALS-REx oceanographic mesoscale surveyand satellite data to determine the hori-zontal and vertical eddy structure, eddyheat/freshwater/biota transports from thecoastal upwelling region to the remoteSEP, and interactions between the eddies,the mixed layer and the deeper ocean. • Aerosol-cloud-drizzle-ocean interac-tions: VOCALS-REx data will be used toconstrain and refine parameterizations ofaerosol scavenging, cloud fraction andcloud microphysical processes used inparticipating AGCMs and RAMs.• Diagnostic studies of the regional cli-mate system: RAMs, ROMs andRegional Ocean-Atmosphere Models(ROAMs) will be used to investigate thecoupling between the atmosphere, oceanand land in the SEP region.

• Modeling biogeochemical processes:VOCALS will accelerate the process bywhich a representation of the interactionsbetween ocean biota and the climate sys-tem are included in climate models. • Development of a Multi-ScaleSimulation and Prediction (MUSSIP)System: VOCALS-Mod will use a Multi-Scale Simulation and Prediction (MUS-SIP) system based on a RAM coupled toan eddy-resolving ROM embedded with-in a global climate model or forced byreanalysis data. • Strategy: The VOCALS modelingvision is based on the concept of a multi-scale hierarchy of models reflecting themultiscale nature of processes in the SEPand the multiscale hierarchy of VOCALSobservations. VOCALS-Mod will coor-dinate activities carried out at operationalcenters (NCEP), research laboratories(NCAR, GFDL) and universities, withthe goal of using VOCALS observationaldatasets both to evaluate model perform-ance and to inform physical parameteri-zation development. Use of the opera-tional modeling systems will provideinsight into the time evolution of errorsand their dependency on the analysisemployed for initialization; use ofresearch modeling systems will facilitatethe realization of hypothesis-testingexperiments. The collaborations estab-lished willl make available the hierarchyof numerical models needed to addressthe broad range of space and time scalesof processes in the VOCALS region.The VOCALS Legacy

VOCALS has been conceived withthe overarching goal of improving largescale coupled ocean-atmosphere modelsimulations and predictions of the SEPclimate system. This will be achievedwith a coordinated modeling and obser-vational program, in which datasets areidentified, generated and shared througha VOCALS-wide data archive. Datasetsgenerated will be made available to thebroad modeling community as soon asquality control is completed. A multi-scale simulation and prediction systemwill be developed. VOCALS will pavethe way for field campaigns in the stra-tocumulus regions in the eastern tropicalAtlantic, which influence the western

A ship towing the SeaSoar platform willbe used to conduct a survey of themesoscale eddy field at several distancesfrom the coast. Detailed measurements ofthe microscale variability of the upperocean will be used to explore the connec-tions between the ocean mixed layer andthe ocean beneath. Chilean and Peruviancoastal components are expected to pro-vide key data on the nature of theupwelling and the initiation of themesoscale eddies. Links between thevariability in oceanic upwelling and thebiogenic production of important aerosolprecursor gases (e.g. DMS) will beexplored using DMS flux measurements.In addition, the role of the land at modi-fying the diurnal cycle (Garreaud andMuñoz 2004) and synoptic variability ofclouds and low level winds will beexplored.

An additional key V O C A L S - R E xgoal is to use the unparalleled combina-tion of cloud measurements and otherobservational datasets to critically evalu-ate the accuracy of current and futuresatellite cloud microphysical retrievalalgorithms. d. Strategy

VOCALS-REx will have an intenseobserving period during October-November 2008. The observational plat-forms during the period will compriseaircraft (chiefly the NSF C-130, the CIR-PAS Twin Otter, the DOE G-1, and possi-bly the UK BAe-146), research ships (theNOAA Ronald H Brown (RHB), and pos-sibly a second ship), a land site in Chile,and Peruvian and Chilean coastal cruises.Figure 4 shows a map of the VOCALS-REx study region and platforms involved.VOCALS-Rex activities have been care-fully designed to complement andenhance a suite of enhanced long-termobservations in the SEP. These includean uninterrupted six year record from theIMET instrumented surface buoy (85°W,20°S), annual buoy maintenance cruises(in 2001 and then in 2003-2006), andregionally-subsetted satellite data.VOCALS-Mod• Goals: A principal goal of VOCALSis to improve model simulations of keyclimate processes using the SEP as a test-bed, particularly in coupled models that


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Variability. Monthly Weather Review: 133,2246–2261.

GEIA: Global Emissions InventoryA c t i v i t y, an integrating project of theAIMES/IGBP programs. See http://geiacen-ter.org/

Gordon C. T., A. Rosati, R. Gudgel, 2000:Tropical sensitivity of a coupled model tospecified ISCCP low clouds. J. Clim., 13,2239-2260.

Huneeus, N., L. Gallardo, and J. A .Rutllant, 2006: Offshore transport episodes ofanthropogenic sulfur in Northern Chile:Potential impact upon the stratocumulus clouddeck. Geophys. Res. Lett., 33, L19819,doi:10.1029/2006GL026921.

Kiehl, J. T., and P. R. Gent, 2004: TheCommunity Climate System Model, version2. J. Climate., 17, 3666–3682.

Large W. G., and G. Danabasoglu, 2006:Attribution and impacts of upper-ocean biasesin CCSM3. J. Climate, 19, 2325–2346.

Lohmann, U., and J. Feichter, 2005:Global indirect aerosol effects: a review.Atmos. Chem. Phys. Disc., 5, 715-737.

Ma, C.-C., C.R. Mechoso, A . W.Robertson and A. Arakawa, 1996: Peruvianstratus clouds and the tropical Pacific circula-tion: A coupled ocean-atmosphere GCMstudy. J. Cli¬mate, 9, 1635-1645.

Mechoso, C. R., and coauthors, 1995:The seasonal cycle over the tropical Pacific incou¬pled ocean-atmosphere general circula-tion models. Mon. Wea. Rev., 123, 2825-283.Mitchell, T.P. and J.M. Wallace, 1992: The

annual cycle in equatorial convection and seasurface temperature. J. Climate, 5, 1140-1156.

Penven, P., V. Echevin, J. Pasapera, F.Colas, and J. Tam, 2005: Average circulation,seasonal cycle, and mesoscale dynamics of thePeru Current System: a modeling approach. J.Geophys. Res., 110, 10.1029/2005JC002945.

Richter, I., and C. R. Mechoso, 2006:Orographic influences on the subtropical stra-tocumulus. J. Atmos. Sci., 63, 2585-2601.

Stevens, B., G. Vali, K. Comstock, R.Wood, M. C. van Zanten, P. H. Austin, C. S.Bretherton, and D. H. Lenschow, 2004:Pockets of open cells (POCs) and drizzle inmarine stratocumulus. Bull. A m e r. Meteor.Soc., 86, 51-57.

Wijesekera H.W, and M. C. Gregg, 1996:Surface layer response to weak winds, wester-ly bursts, and rain squalls in the westernPacific Warm Pool. J. Geophys. Res., 101,977-997

Wittenberg, A. T., A. Rosati, N-C. Lau,and J. J. Ploshay, 2006: GFDL's CM2 GlobalCoupled Climate Models. Part III: TropicalPacific climate and ENSO. J. Clim., 19, 698-722.

Wood, R., 2006: The rate of loss of clouddroplets by coalescence in warm clouds. R.Wood, J.Geophys. Res., 111, D21205,doi:10.1029/2006JD007553.

Xie, S. -P., 1996: Westward propagation oflatitudinally asymmetry in a coupled ocean-atmosphere model. J. Atmos. Sci., 53, 3236-3250.

African summer monsoon. In addition,VOCALS will provide education andtraining for both U.S. and regional cli-mate scientists.

ReferencesBretherton, C. S., T. Uttal, C. W. Fairall,

S. Yuter, R. Weller, D. Baumgardner, K.Comstock, R. Wood, and G. Raga, 2004: TheEPIC 2001 stratocumulus study. Bull. Amer.Meteor. Soc., 85, 967-977.

Canuto, V. M. and M. S. Dubovikov,2005: Modeling mesoscale eddies. OceanModeling, 8, 1-30.

Colbo, K. and R. A. Weller, 2006: Thevariability and heat budget of the upperocean under the Chile-Peru stratus. J.Marine. Res., in press.

Collins, W., and coauthors, 2006: TheCommunity Climate System Model Version3 (CCSM3). J. Climate, 19, 2122-2143.

Chelton, D. B., M. H. Freilich, J. M.Sienkiewicz and J. M. Von Ahn. 2006: Onthe Use of QuikSCAT S c a t t e r o m e t e rMeasurements of Surface Winds for MarineWeather Prediction. Monthly We a t h e rReview, 134, 2055–2071.

Garreaud, R. D., and R. C. Muñoz, 2004:The diurnal cycle in circulation and cloudi-ness over the subtropical southeast Pacific:A modeling study. J. Climate, 17. 1699-1710.

Garreaud, R. D., and R. C. Muñoz, 2005:The Low-Level Jet off the West Coast ofSubtropical South America: Structure and

Figure 4. VOCALS-REx study region and key plat-forms/components involved. The RHB will make station-ary measurements at 3 locations (20S and 75, 80, and85W). Ideally, a second ship will make butterfly patternswith the SeaSoar platorm to survey ocean mesoscalevariability. The C-130 will make cross-sectional meas-urements along 20S out to 85W, and conduct flights tostudy the sturcture of pockets of open cells (POCs). Theother aircraft will work mainly in the near-coastal zone toexamine aerosol, cloud and drizzle variability. TheChilean and Peruvian coastal components will involvecoastal ship sampling of the upper ocean and marineboundary layer. The Chilean land site will be used toexamine the chemical and physical properties of the airmasses that are advected from Chile over the SEP.


U.S. CLIVAR

U.S. CLIVAR recently formeda Working Group to providefunding agencies and existingscientific steering groups

with specific guidance on research needsfor improving prediction and monitoringtools for long-term (multi-year) droughtsand to energize initial drought activities.Such droughts have tremendous societaland economic impacts on the UnitedStates, and many other countriesthroughout the world. Estimates of thecosts of drought to the United Statesalone range from $6-$8 billion annuallywith major droughts costing substantiallymore (e.g., $62B in 1988 according toNOAA). The Dust Bowl drought of the1930s, which at its maximum extent cov-ered much of the continental U.S. (Fig. 1)is ranked as one of the top 10 domesticweather-related disasters of the 20th cen-t u r y. Recent population increases inwater-limited regions has increased vul-nerability to drought at the same timethat climate change projections suggestthat drought conditions may becomemore extreme in the 21st Century, partic-ularly in the southwestern United States(NRC, 2007).

Several agencies including NOAAand NASA are in the planning phase forimplementing the National Integrated

Drought Information System (NIDIS,2004) authorized by law in December2006. The vision for NIDIS is a dynamicand accessible drought risk informationsystem that provides users with the abilityto determine the potential impacts ofdrought, and the decision support toolsneeded to better prepare for and mitigatethe effects of drought. As the designatedlead agency, NOAA is developing aninteragency implementation plan. NASAis also engaged in planning for NIDIS aspart of an overall strategy to implementkey aspects of the international GlobalEarth Observation System of Systems(GEOSS) strategic plans.

While NIDIS has a strong focus on theU.S., it is clear that drought is a globalphenomenon, both in terms of the forcingelements and the potential commonalityof local processes that operate to makesome regions more susceptible to droughtthan others. As such, confidence in ourunderstanding of drought processes(remote and local forcing, feedbacks, etc.)will be significantly advanced by effortsto properly analyze and simulate regionaldrought wherever it occurs. Recent stud-ies (e.g., Hoerling and Kumar 2003;Schubert et al. 2004; Seager et al. 2005)suggest that such simulations are feasibleusing current global models (Fig. 2).There are, however, still major uncertain-

ties about the relative roles of the differ-ent ocean basins, the strength of the land-atmosphere feedbacks, the role of deepsoil moisture, the nature of long-termS S T v a r i a b i l i t y, the impact of globalchange, as well as fundamental issuesabout predictability of drought on multi-year time scales.

The primary objective of the U.S.CLIVAR Working Group is to facilitateprogress on the understanding and pre-diction of long-term (multi-year) droughtover North America and other drought-prone regions of the world, including anassessment of the impact of globalchange on drought processes. The specif-ic tasks of the Working Group will be to:1) coordinate and encourage the analysisof observational data sets to revealantecedent linkages of multi-yeardroughts; 2) propose a working defini-tion of drought and related model predic-tands of drought, 3) coordinate evalua-tions of existing relevant model simula-tions, 4) suggest new experiments (cou-pled and uncoupled) designed to addresssome of the uncertainties mentionedabove, and to contribute to NIDIS-relat-ed drought risk assessment; 5) examinethe prospects for using land data assimi-lation products for operational monitor-ing, assessment and hydrological appli-cations; and 6) organize an open work-shop in 2008 to present and discuss theworking group results and considerresults from the community.

As initial products, the Wo r k i n gGroup is compiling a list of recent paperson drought research, and an inventory ofaccessible data sets for observationalstudies. These products (still underdevelopment) can be obtained throughthe Working Group’s web page ath t t p : / / w w w. u s c l i v a r. o rg / O rg a n i z a t i o n / d rought-wg.html. The Working Group hasalso initiated discussion of a workingdefinition of drought (including onsetand demise) for use by both the predic-tion/research and applications communi-ties. The goal of this effort will be to

The U.S. CLIVAR Working Group on Long-term DroughtDave Gutzler, University of New Mexico, co-chair

Siegfried Schubert, NASA Goddard Space Flight Center, co-chair

Figure 1. Spatialextent of the DustBowl drought of the1930s in August 1934.Percentiles are for soilmoisture relative to the85-year period 1915-2003. From Universityof Washington SurfaceWater Monitor, avail-able online at:http://www.hydro.washington.edu/forecast/monitor.


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(with its focus on large scale and ocean-atmosphere coupling), and GEWEX(focusing on regional scales and land-atmosphere coupling). What is the roleof the land (e.g., deep soil moisture,snow, vegetation)? What is the role ofthe different ocean basins, including theimpact of ENSO, the PDO, the AMO,and longer term warming trends in theglobal oceans? To what extent candrought develop independently ofocean variability due to year-to-yearmemory inherent to the land?

The Working Group will recom-mend and promote a set of idealizedexperiments coordinated among differ-ent models to address some of the keyissues outlined above (e.g., role of dif-ferent ocean basins, deep soil moisture,etc.). Specific details about the experi-ments and diagnostic analyses arebeginning to be developed. T h eWorking Group will coordinate withresearch institutes and universitiesactive in drought research to ensure thatthe relevant simulations are well docu-mented and accessible to the communi-ty.

New simulations will build uponthe climate variability and change attri-

bution activities funded byNOAA/CDEP, the attribution and pre-diction capabilities at various universi-ties and research institutes, and takeadvantage of the many long term cou-pled model runs that have been conduct-ed as part of the IPCC climate changeassessment process. The upcoming DRI-COMP( h t t p : / / w w w. u s c l i v a r. o rg / D R I C O M P -AO.html) model assessment researchopportunity represents an importantcomponent of this effort. Additionalactivities of the Drought Working Groupcan be monitored on its web page:h t t p : / / w w w. u s c l i v a r. o rg / O rg a n i z a t i o n / d rought-wg.html).

ReferencesHoerling, M.P. and A. Kumar, 2003: The

perfect ocean for drought. Science, 299, 691-699.

IEOS, 2005: Strategic Plan for the U.S.Integrated Earth Observation System. TheInteragency Working Group on EarthObservations. NSTC Committee onEnvironment and Natural Resources.Available online at: http://iwgeo.ssc.nasa.gov/

NIDIS, 2004: Creating a Drought EarlyWarning System for the 21st Century: TheNational Integrated Drought InformationSystem (NIDIS). A report of the NationalOceanic and Atmospheric A d m i n i s t r a t i o nand the Western Governor’s A s s o c i a t i o n .Available onlin: http://www.westgov.org.

NRC, 2007: Colorado River Basin WaterManagement: Evaluating and Adjusting toHydroclimatic Variability. Available online:h t t p : / / b o o k s . n a p . e d u / c a t a l o g . p h p ? r e c o r d _ i d =11857

Schubert S. D., M. J. Suarez, P. J. Pegion,R. D. Koster, and J. T. Bacmeister. 2004: Onthe cause of the 1930s Dust Bowl. Science,303, 1855–1859, doi: 10.11 2 6 / s c i-ence.1095048.

---, R. Koster, M. Hoerling, R. Seager, D.L e t t e n m a i e r, A. Kumar, and D. Gutzler,2005: Observational and ModelingRequirements for Predicting Drought onSeasonal to Decadal Time Scales. Availableonline at: http://gmao.gsfc.nasa.gov/pubs/

Seager, R., Y. Kushnir, C. Herweijer, N.Naik, and J. Velez, 2005: Modeling of tropi-cal forcing of persistent droughts and pluvialsover western North America: 1856-2000. J.Climate, 18, 4068-4091.

define drought in a way that is quantifi-able and verifiable for the purpose ofmodel prediction experiments, as well asfor drought monitoring and early warn-ing, and facilitating communicationbetween the applications andmodeling/research communities.

The working group will help coordi-nate key aspects of the long-term droughtresearch agenda outlined in the recentdrought workshop recommendations(e.g. Schubert et al. 2005). It will interactwith the developing NIDIS program tocommunicate current drought predictionand attribution capabilities. The WorkingGroup will work with the NIDIS commu-nity and the relevant funding agencies todevelop guidance on drought researchneeds, based on assessments of predic-tion capabilities and input we will seekconcerning stakeholder-driven predictionpriorities. It will advocate the coordina-tion of efforts among the agencies toadvance drought prediction research inways that will maximize the utility forNIDIS development.

The long-term drought problem canbe an important umbrella issue to bringtogether the relevant research expertiseof the International CLIVAR program

Figure 2. Time series of precipitation anomalies averaged over the U.S. GreatPlains region (30°N to 50°N, 95°W to 105°W), from Schubert et al. (2004). A filterhas been applied to remove time scales shorter than about 6 years. The thinblack curves are the results from 14 ensemble members from C20C global modelruns. The green solid curve is the ensemble mean. The red curve is based onobservations. The maps show the simulated (left) and observed (right) precipita-tion anomalies averaged over the Dust Bowl period (1932 to 1938, units mm/day).


U.S. CLIVAR

The North American MonsoonSystem (NAMS) is consideredto be the principle organizingstructure for the warm season

limate of southwestern North America.Like its global, though often larg e r,counterparts in Asia, Australia, Africaand South America, the NAMS exhibitsmarked seasonal reversals in land-oceanthermal contrasts, low and mid-tropos-pheric wind fields, atmospheric moistureconvergence patterns, atmospheric sta-bility and, consequently, precipitation.The seasonal onset, intensity and decayof summer rains drive a host of ecologi-cal and societal dependencies rangingfrom water resources to wildland firethreat to rangeland forage production toenergy supply and demand to estuarinefisheries (cf Ray et al., 2007; Aragón andGarcía, 2002; Gochis et al., 2006,2007a). However, also like its globalcounterparts, prediction skill of warmseason rainfall on seasonal to interannu-al timescales remains critically low. Thislack of skill translates into a persistentvulnerability of the aforementioneddependencies. The 2006 summer mon-soon, which brought persistent heavyrainfall to the U.S.-México border region(Sonora, Chihuahua, Arizona and NewMexico) and tens of millions of dollarsin damages, served as a timely reminderof this vulnerability (cf FEMA, 2007,CLIMAS, 2006).The NAME Program:

The North American MonsoonExperiment (NAME) is a continental-scale process study now in its seventhyear that was conceived to directlyaddress the issue of improving predic-tions of warm season precipitation inNorth America. The NAME program isjointly sponsored by Climate Variability

The Path to Improving Predictions of the

North American MonsoonDavid J. Gochis, National Center for Atmospheric Research

R. Wayne Higgins, Climate Prediction Center/NOAA/NWS/NCEP

and Predictability (CLIVAR) andGlobal Energy and Water CycleExperiment (GEWEX) research efforts.The underlying hypothesis of NAME isthat the structure and evolution of theNAMS provides a physical basis fordetermining the degree of predictabilitywarm season precipitation over much ofNorth America. A fundamental first steptowards improved prediction is the cleardocumentation of the major elements ofthe monsoon system and their variabili-ty within the context of the evolvingOcean-Atmosphere-Land (O-A-L)annual cycle (Higgins and Gochis,2007). To achieve this NAME employsa multi-scale (tiered) approach withfocused monitoring, diagnostic andmodeling activities in the core monsoonregion, on the regional-scale and on thecontinental-scale (Fig. 1). (Additional

detail on NAME background informa-tion and motivating science questionscan be found in Higgins et al., 2006 andNAME-SWG, 2007).

Central to the NAME research effortis a list of science questions posed onthe three tiers of the NAME studydomain. These questions are aimed atimproving the understanding and simu-lation of 1) warm season convectiveprocesses over complex terrain (Tier I),2) the modes and drivers of intra-sea-sonal variability (Tier II) and, 3) theresponse of the NAMS to oceanic andcontinental boundary conditions (TierIII). The timeline for NAME activities(Fig. 1) encompasses planning, data col-lection and principle research phases. Aprogressive aspect of NAME has beenthat modeling and data assimilationactivities were engaged early in plan-ning process in order to guide the obser-vational strategy of a large EnhancedObserving Period (EOP) or, field cam-paign, which was conducted during thesummer of 2004. This coordinationinsured that the field data collected notonly would serve as valuable data forconducting exploratory and diagnosticanalysis, but would also directly addressproblematic modeling issues that hadarisen through numerous prior modeling

Figure 1. Multi-tieredresearch domain devel-oped for NAME.Important features of themonsoon climate are alsodepicted. Digonal redlines indicate eastward(mid-latitude) and west-ward (tropical) propagat-ing transients known toimact monsoon behavior.Wind vectors indicate themean 925hPa wind fieldfrom the NCEP/NCARreanalysis. Green shad-ing indicates mergedsatellite estimates andraingauge observatins ofprecipitation in millime-ters. The timeline forNAME program, begin-ning in 2000, is alsoshown. (Adapted fromHiggins et al., 2006)


VARIATIONSstudies. These issues included the struc-ture and evolution of regional moistureflux patterns over the Gulf of California(GoC), air-sea interactions over the GoCand Eastern Pacific, the diurnal cycle ofprecipitation, upscale organization andpropagation of convection, the influenceof low-and mid-latitude transients on pre-cipitation episodes and coupling betweenthe land-surface and the atmosphere. TheNAME 2004 EOP was organized andconducted by an international coalition ofuniversity and agency scientists, and fore-casters from México, the U.S. and centralAmerica. More than 20 different types ofinstrument platforms, including surfacemeteorological stations, radars, aircraft,research vessels, satellites, wind profilers,rawinsondes, pibals, rain gauge networks,soil moisture sensors and GPS integratedwater vapor retrieval antennae weredeployed within the Tier I and II regionsin Figure 1. (Higgins and Gochis, 2007)

The remainder of this article providesa brief overview of the key findings fromthe 2004 EOP as well as a discussion oncurrent activities aimed at improving pre-dictions of warm season precipitationover North America. Given the brevity ofthis summary only a few topics are high-lighted. The summary provided belowalong with much of the work cited is con-tained in a forthcoming special issue inthe Journal of Climate on NAME due tobe published during the late-spring of2007, and in meeting reports from theNAME SWG from 2005 and 2006 avail-able through the official NAME website(http://www.eol.ucar.edu/projects/name/)Key Findings from 2004 EOP:Regional circulation stru c t u res aro u n dthe Gulf of California (GoC):

Owing to marked deficiencies in thepre-existing operational sounding net-work over the NAMS region, characteri-zation of the atmospheric circulation inthe Gulf of California region was greatlyenhanced during the 2004 NAME EOP.Time mean analyses of NAME 2004observations, conceptualized in Figure 2,show strong low-level convergence andupper-level divergence along the crest ofthe Sierra Madre Occidental (SMO)(Johnson et al., 2007). This direct circula-tion structure, centered over western

México, is considered to be the principledriver of the NAMS. Peripherally,strong subsidence was found to persistover the Gulf of California as a result ofreturn flow from sea-breeze/terrain cir-culation and from flow descending overthe SMO (Johnson et al., 2007; Zuidemaet al., 2007). Despite the enhancedobserving network present during 2004,significant uncertainty in the verticalhumidity structure over the complex ter-rain exists due to lack of surface meteor-ological and atmospheric observations.

Flow over the GoC and the westerncoast of the Mexican mainland was typi-fied by nocturnal low level southeasterlyflow and daytime low-level westerlyflow inland towards the SMO. Easterliestend to persist at middle and upper levelsfostering a light to moderately shearedenvironment over the principle convec-tive region of the western slope of theSMO. Divergence, vertical motion,heating and moistening profiles derivedfrom analyses of the special observationsare all consistent with a convectively-dominated dynamical system (Johnson etal., 2007). Nevertheless, stratiform pre-cipitation structures were frequentlyobserved during nighttime hours and areassumed to play an important role inmodifying the regional thermodynamicstructure over and around the GOC

(Johnson et al., 2007; Zuidema et al.,2007; Williams et al., 2007).

C l i m a t o l o g i c a l l y, inverted troughsand other synoptic transients such as trop-ical easterly waves, and westerly mid-lat-itude troughs are critical features of theNAM (Douglas and Englehart, 2007).Inverted troughs, propagating along thesouthern limb of the summertime sub-tropical anticyclone, help advect moistureand provide dynamical support by meansof large scale ascent and orographic lift inotherwise dry regions such as the centralMexican Plateau. In addition to having alate onset, synoptic variability during2004 summer monsoon was characterizedby a reduced number of inverted troughsand nearly twice the climatological num-ber of midlatitude westerly troughs(Douglas and Englehart, 2007). T h ewesterly troughs during 2004 were impli-cated in drier-than-normal conditions inArizona and northern Sonora but wetterthan normal conditions in eastern NewMexico. On interannual timescales thedominance of a particular transientregime significantly influences summerrainfall patterns (Douglas and Englehart,2007). Characteristics of Precipitation:

Forcing of the diurnal cycle of winds

Figure 2. Schematic of regionalcirculation features of the NorthAmerican Monsoon. Heavyblue lines in plan view desig-nate principle moisture path-ways. ‘H’ an d ‘L’ indicate clima-tological positions of hte upper-level monsoon anticyclone andhte low-level desert thermallow, respectively. Cross-sectionin top figure is approximatedfrom heavy black dotted line onmap. Cloud structures in greyshading approximate thosestructures diagnosed from vari-ous precipatation studies con-ducted as part of NAME.(Adaped from Johnson et al.,2007, Higgins et al., 2006,Nesbitt and Gochis, 2007).


U.S. CLIVAR

AMS Air-Sea Interaction Conference20-24 August 2007Portland, OregonAttendance: OpenContact: http://www.ametsoc.org

Layered Ocean Model Meeting20-23 August 2007Bergen, NorwayAttendance: OpenContact: www.clivar.org

CLIVAR Working Group on OceanModel Development26-27 August 2007Bergen, NorwayAttendance: InvitedContact: http://www.clivar.org

2nd International Conference onEarth System Modeling27-31 August 2007Hamburg, GermanyAttendance: OpenContact: http://www.mpimet.de/icesm

CLIVAR SSG-1511-14 September 2007Geneva, SwitzerlandAttendance: InvitedContact: http://www.clivar.org

AMS Conference on SatelliteMeteorology and Oceanography andOcean Vector Winds Science Team24-28 September 2007Amsterdam, NetherlandsAttendance: OpenContact: http://www.conferences.eumet-sat.int

PICES 16th Annual Meeting: TheChanging North Pacific: Previous pat-terns, future projections and ecosys-tem impacts26 October - 5 November 2007Victoria, British ColumbiaAttendance: OpenContact: http://www.pices.int/meetings

Variability of the American Monsoons(VAMOS-10)2-5 April 2007Santiago, ChileAttendance: InvitedContact: http://www.clivar.org

Int'l Oceanographic Data andInformation Exchange (IODE)16-20 April 2007Trieste, ItalyAttendance: OpenContact: http://www.iode.org

CLIVAR Indian Ocean Panel Meeting23-25 April 2007South AfricaAttendance: InvitedContact: http://www.clivar.org

Seventh Workshop on Decadal ClimateVariability30 April-3 May 2007Kona, HawaiiAttendance: OpenContact: http://www.decvar.org/work-shops_conferences.php

Ocean Observataions Panel forClimate-1230 April-4 May 2007Melbourne, AustraliaAttendance: InvitedContact: http://www.clivar.org

AGU Joint Assembly21-25 May 2007Acapulco, MexicoAttendance:OpenContact: http:// www.agu.org

WCRP Workshop on SeasonalPrediction4-8 June 2007Barcelona, SpainAttendance: OpenContact:http://www.wmo.ch/web/wcrp/AP_SeasonalPrediction.html

NOAA Climate Observation AnnualReview5-7 June 2007Silver Spring, MarylandAttendance: OpenContact: http://www.oco.noaa.gov

Pacific Science Congress XXISymposium on Global Change, AsianMonsoon and Extreme Weather andClimate 12-16 June 2007Okinawa, JapanAttendance: OpenContact: http://www.psc21.net

12th Annual Community ClimateSystem Model (CCSM) Workshop18-21 June 2007Breckinridge, COAttendance: OpenContact: http://www.ccsm.ucar.edu

IEEE Oceans ‘0718-21 June 2007Aberdeen, ScotlandAttendance: OpenContact: http://www.oceans07ieeeab-erdeen.org/

IUGG 20072-13 July 2007Perugia, ItalyAttendance: OpenContact: http://www.iugg2007perugia.it/

U.S. CLIVAR Summit23-25 July 2007Annapolis, MarylandAttendance: InvitedContact: www.usclivar.org

Application of Remotely SensedObservations in Data Assimilation23 July - 10 August 2007College Park, MarylandAttendance: OpenContact:http://www.essic.umd.edu

Calendar of CLIVAR and CLIVAR-related meetingsFurther details are available on the U.S. CLIVAR and International CLIVAR web sites: www.usclivar.org and www.clivar.org

U.S. CLIVAR


is supplied by land-sea contrasts andthe heating of elevated terrain and thesecirculations significantly influence thediurnal cycle of precipitation. As aresult, precipitation character (e.g. fre-quency, intensity and duration) is oftenrelated to variations in local (O~1-10km) and regional (O~10-100 km) ter-rain features, land-sea contrasts andaccess to abundant atmospheric mois-ture (Gebremichael et al., 2007; Gochiset al., 2007b; Janowiak et al., 2007;Lang et al., 2007; Vivoni et al., 2007).Numerous studies now confirm a pre-cipitation climatology in which precip-itation forms most frequently and earli-est in the afternoon over the highest ter-rain, albeit with comparatively lightintensity, and less frequently and laterduring the evening but with heavierintensities over the low elevationcoastal regions. While a large fractionof the regional precipitation climatol-ogy is dominated by events whoseentire life cycles occur over the com-plex terrain of the SMO, a secondary,‘disturbed’ regime is now recognizedunder which organized, propagatingprecipitation events move away fromtopography (Lang et al., 2007). Radarcomposite products collected during2004 also capture the complex interac-tions between the regional circulation,the land-sea breeze and propagatingorganized precipitation events over theGoC. Notably, precipitation over theGoC is about 12 hours out of phasewith precipitation occurring over theSMO (Lang et al., 2007; Zuidema et al.,2007). Long-lived stratiform precipita-tion structures, characterized by strongbrightband signatures in radar and ver-tically-pointing profilers, are very sig-nificant and, at times, a dominantmechanism for precipitation (Lang etal., 2007; Williams et al., 2007).Retrievals from NOAA wind profilersand space-borne radar show a relative-ly strong dependence on microphysicalstructures, in particular brightbanding(Williams et al., 2007). Strong spatialand temporal variations in cloud ther-mal and microphysical characteristicspresent significant challenges in esti-mating precipitation from remote sens-ing platforms (Nesbitt and Gochis,2007).

Ocean-Land-Atmosphere Coupling:Onset of the 2004 monsoon was

associated with the southeasterly advec-tion of warm water from the tropicalEast Pacific Ocean into the GoC(Zuidema et al., 2007). Throughout thes u m m e r, oceanographic observationsnear the mouth of the GoC documentedthat strong solar heating, ocean heatadvection and nighttime cloudiness overthe Gulf provide a positive feedbackresulting in net surface heating despite al a rge evaporation component.Furthermore, periodic, strong advectionof warm water from the southeast duringatmospheric moisture surge events alsoappears to contribute to a surge-memoryeffect as the recently advected watercontributes to the latent and sensiblefluxes within the Gulf region.Capturing the complex, transient behav-ior of the GoC heat and moisture sourcewill be essential for improving modelsimulations and highlights the impor-tance of resolving the Gulf in free run-ning climate models.

Strong latitudinal and terrestrial gra-dients in terrestrial hydrology and ecol-ogy are found throughout the monsoonregion. These variations act as a dynam-ic assimilator of atmospheric processesyet their influence as an atmosphericdriver (ie the nature of the land-atmos-phere feedback) remains uncertain(Vivoni et al., 2007; Watts et al., 2007;Zhu et al., 2007). During 2004, towerflux and soil moisture measurementswere made in a variety of ecotones(transition areas between two adjacentecosystems). From a vegetation biomeperspective tropical deciduous forestsrespond much more quickly and strong-ly to precipitation than other semi-aridcommunities (Watts et al., 2007).Notably, the tropical deciduous forestsexhibit slower decay of evapotranspira-tion fluxes under moisture stress thanmany other communities eff e c t i v e l yresulting in a ‘quick learning-long for-g e t t i n g ’ b e h a v i o r. On seasonal andinterannual timescales antecedent landsurface conditions across southwesternNorth America affect the timing of theonset of monsoon precipitation by mod-ulating the land-sea thermal contrast(Grantz et al., 2007, Zhu et al., 2007).

These anomalies are largely establishedin response to antecedent cold-seasonprecipitation anomalies which varygreatly from year to year. This regionalforcing acts in concert or competitionwith large-scale teleconnective forcingprovided by remote and near shore seasurface temperatures (Grantz et al.,2007, Gochis et al., 2007a). Towards Improving Predictions

Transferring this emerging under-standing of the NAMS into improvedpredictions of warm season precipitationwill not be easy. Fundamental limita-tions still exist in the observing systemover parts of México, in particular theSMO, the intra-America Seas region,and the tropical oceans in general. Poortreatment of convection in models andlimited understanding of role of terres-trial forcing will continue to inhibitrapid increases in seasonal and inter-annual forecast skill from dynamic mod-els. However, as part of NAME,progress is being made on definingwhich observations are critical toimproving model initializations andforecasts. Assimilation of NAME 2004special soundings into NCEP model-based data assimilation systems indi-cates that impacts of the soundings aremost pronounced at low levels in theatmosphere and mainly in the core mon-soon region of northwestern México andthe southwestern U.S. where the sound-ing data were collected (Mo et al.,2007). Enhanced sounding observa-tions also had a significant and benefi-cial impact on depicting the structure ofthe Gulf of California low-level jet.However, additional data impact studiesof the NAME 2004 enhanced observa-tions, such as sea surface temperatures,rain gauge observations, and soil mois-ture measurements, on atmosphericanalyses are needed. These studies will,over time, contribute to the developmentof an observing system design for theNAMS which is key deliverable fromthe NAME program.

Comparatively less progress hasbeen made in addressing NAMEresearch questions in Tiers II and IIIcompared to Tier I. While this is under-standable, given the focus of NAME

VARIATIONS


U.S. CLIVAR2004, the research issues in Tiers II andIII need to have greater priority in thefuture in order to make progress onwarm season precipitation forecasts.The 2004 monsoon highlighted the sig-nificant dependence of monsoon precip-itation, in many regions, on transientsynoptic features. For instance, mois-ture surge activity appears to beenhanced during active phases of theMadden Julian Oscillation (Johnson etal., 2007; Lorenz and Hartmann, 2006).Similarly, Mestas-Nunez et al. (2007)show that variability in the transportfrom the key moisture source region ofthe intra-America Seas is linked tochanges in summertime precipitationpatterns over the central and easternU.S. It has become clear that there arecomplex interactions between tropicaleasterly waves, upper-level invertedtroughs, cold fronts, cut-off lows, opentroughs, and GoC moisture surges thatare not well understood despite the factthat they are critically important in theprediction of warm season precipitation.

As NAME enters into its modelingand prediction phase many significantchallenges remain. Some of these are‘grand challenge’ issues, such as therepresentation of convection in modelsor land-ocean-atmosphere coupling, thatextend well beyond NAME. Moreimportantly, in order to improve predic-tions of warm season precipitation,NAME will need to engage a variety ofstrategies aimed at detecting criticalenvironmental processes that modulatethe warm season circulation andimproving the representation of theseprocesses in empirical and dynamicalprediction models. One way forward, asmentioned previously, is to design andmaintain a robust climate observing sys-tem across the southern North Americancordillera, the GoC and the intra-America Seas regions. This need hasalso been identified in the context ofother climate variability and climatechange research efforts recently articu-lated by Diaz et al. (2006) and Diamondand Helfert (2007).

Second, NAME must also engageefforts to provide added value to exist-ing forecast methodologies in order tocreate more usable warm season fore-

cast products. One way NAME isaddressing this issue is by developingthe NAME Forecast Forum which willconsolidate a variety of operational andexperimental forecast products of mon-soon activity. This new effort will buildupon the success of the NAME ModelAssessment Project (NAMAP s e eGutzler et al., 2006 for details), whichhas documented the attributes andshortcomings of several leading globaland regional models in the simulation ofmonsoon circulation and precipitationfeatures. More detail on this effort willbe forthcoming in the coming monthsthough interested parties are encour-aged to contact the authors directly.Another way for NAME to add value toexisting forecasts is by improving theapplication of dynamical and statistical-dynamical downscaling techniques inseasonal forecasts. While suchapproaches clearly can not correct forerroneously forecasted climatic struc-tures, they can serve to better transferinformation captured in forecasted cli-mate modes to smaller scale, regionalclimate processes such as variable pre-cipitation characteristics across com-plex terrain. As has been the case fromthe beginning of NAME, it will bethrough a synthesis of multi-discipli-nary activities that measured progress inimproved understanding of the mon-soon system will be transferred intoimproved prediction capabilities.

References:Aragón, E.A. and A. García, 2002:

Postlarvae recruitment of blue shrimpLitopenaeus stylirostris (Stimpson, 1871) inantiestuarin conditions due to anthropogenicactivities. Hidrobiológica, 12(1), 37-46.

CLIMAS, 2007: Southwest climate out-look – August 2006. Online climateOutlook published by the ClimateAssessment for the Southwest (CLIMAS)project. Tucson, Arizona. Available onlineat:h t t p : / / w w w. i s p e . a r i z o n a . e d u / c l i m a s / f o r e-casts/archive/aug2006/swoutlook.html

Diamond, H.J. and M.R. Helfert, 2007:The U.S. Global Climate Observing System(GCOS) Program: Plans for high elevationGCOS surface network sites based on thebenchmark U.S. Climate ReferenceNetwork (CRN) System. Mountain Views,Newsletter of the Consortium for IntegratedClimate Research in Western Mountains

(CIRMOUNT), 1, 16-19.Diaz, H.F., R. Villalba, G. Greenwood

and R.S. Bradley, 2006: The impact of cli-mate change in the American Cordillera.Eos, Transactions of the A m e r i c a nGeophysical Union, 87(32), August, 2006,p. 315.

Douglas, A.V. and P.J. Englehart, 2007:A climatological perspective of transientsynoptic features during NAME 2004. Inpress, J. Climate.

FEMA, 2007: New Mexico severestorms and flooding. Federal EmergencyManagement Agency (FEMA) DisasterInformation web page. Available online at:h t t p : / / w w w. f e m a . g o v / n e w s / e v e n t . f e m a ? i d =6925

Gebremichael, M., E.R. Vivoni, C.J.Watts, and J.C. Rodriguez, 2007: Local-scale spatio-temporal variability of NorthAmerican monsoon rainfall over complexterrain. In press, J. Climate.

Gochis, D.J., L. Brito-Castillo, W. J .Shuttleworth, 2006: Hydroclimatology ofthe North American Monsoon region ofnorthwest México. J. Hydrology, 316, 53-70.

Gochis, D.J., L. Brito-Castillo, W. J .Shuttleworth, 2007a: Correlations betweensea-surface temperatures and warm seasonstreamflow in northwest México. In press,Int’l. J. Climatol.

Gochis, D.J., C.J. Watts, J. Garatuza-Payan, and J.C. Rodriguez, 2007b: Spatialand temporal patterns of precipitation inten-sity as observed by the NAME event raingauge network from 2002 to 2004. Inpress, J. Climate.

G u t z l e r, D. S, H.-K. Kim, R. W.Higgins, et al., 2005: The North Americanmonsoon Model Assessment Project(NAMAP): Integrating numerical modelinginto a field-based process study. Bull.Amer. Met. Soc, 86, 1423-1430.

Lorenz, D.J. and D.L. Hartmann, 2006:The effect of the MJO on the NorthAmerican Monsoon. J. Climate, 19, 334-343.

Higgins, R. W. and co-authors, 2006:The North American Monsoon Experiment(NAME) 2004 Field Campaign andModeling Strategy. Bull. A m e r. Meteor.Soc., 87, 79-94.

Higgins, R.W. and D.J Gochis, 2007:Synthesis of results from the NorthAmerican Monsoon Experiment (NAME)process study. In press, J. Climate.

Janowiak, J.E., V.J. Dagostaro, V. E .Kousky and R.J. Joyce, 2007: An examina-tion of precipitation in observations andmodel forecasts during NAME withemphasis on the diurnal cycle. In press, J.Climate.

Johnson, R.H., P.E. Ciesielski, B.D.


McNoldy, P.J. Rogers and R.J. Taft, 2007:Multiscale variability of the flow during theNorth American Monsoon Experiment. Inpress., J. Climate.

Lang, T.J., D.A. Ahijevych, S.W.Nesbitt, R.E. Carbone, S.A. Rutledge and R.Cifelli, 2007: Radar-observed characteris-tics of precipitating systems during NAME2004. In press, J. Climate.

Mestas-Nuñez, A., D.B. Enfield and C.Zhang, 2007: Water vapor fluxes over theIntra-Americas Sea: Seasonal and interan-nual variability associated with rainfall. Inpress, J. Climate.

NAME Science Working Group, cited2007: North American MonsoonExperiment Science and ImplementationPlan. [Available online ath t t p : / / w w w. c p c . n c e p . n o a a . g o v / p r o d u c t s / m onsoon/NAME.html.]

Nesbitt, S.W. and D.J. Gochis, 2007:Characteristics of convection along theSierra Madre Occidental observed duringNAME-2004: Implications for warm seasonprecipitation estimation in complex terrain.Manuscript in preparation.

Ray, A.J., G.M. Garfin, M. Wilder, M.Vasquez-Leon, M. Lenart and A.C. Comrie,2007: Applications of monsoon research:Opportunities to inform decision makingand reduce regional vulnerability. In press,J. Climate.

Vivoni, E.R., H.A. Gutierrez-Jurado,C.A. Aragon, L.A. Mendez-Barrozo, A.J.Rinehart, R.L. Wycoff, J.C. Rodriguez, C.J.Watts, J.D. Bolten, V. Lakshmi and T.J.Jackson, 2007 : Variation of hydrometeoro-logical conditions along a topographic tran-sect in northwestern México during theNorth American monsoon. In press, J.Climate.

Watts, C.J., R.L. Scott, J. Garatuza-ayan, J.C. Rodriguez, J.H. Prueger, W.P.Kustas and M. Douglas, 2007: Changes invegetation condition and surface fluxes dur-ing NAME 2004. In press, J. Climate.

Williams, C.R., A.B. White, K.S. Gageand F.M. Ralph, 2007: Vertical structure ofprecipitation and related microphysicsobserved by NOAA profilers and TRMMduring NAME 2004. In press, J. Climate.

Zhu, C., T. Cavazos and D.P.Lettenmaier, 2007: Role of antecedent landsurface conditions in warm season precipita-tion over northwestern México. In press, J.Climate.

Zuidema, P. C. Fairall, L.M. Hartten,J.E. Hare and D. Wolfe, 2007: On air-seainteraction at the mouth of the Gulf ofCalifornia. In press, J. Climate.

The Earth’s climate is an ener-gy cycle that convertsabsorbed solar radiation intoheat and associated terrestrial

radiation and into the circulations of theatmosphere and ocean. A key exchangeof energy within the system, which alsocouples the circulations of the atmos-phere and ocean, is between the surfaceand the atmosphere, primarily throughevaporation cooling of the surface andprecipitation heating of the atmosphere,forming a water cycle intimately linkedto the planetary energy cycle. Becauseof Earth’s spherical shape, rapid rota-tion and elliptical orbit about the sun,the solar heating is neither uniform norconstant. Because of the turbulentnature of the atmospheric and oceanicmotions that transport heat and waterwith very different characteristic timesscales, the response of the system is nei-ther steady nor in instantaneous bal-ance. Although some statistics of thevariations of energy and waterexchanges among the several climatesystem components may be static, thee n e rgy-water cycle is fundamentallydynamic.

Basic questions about the climateare: how variable is the climate with a“statistically steady” forcing (naturalvariability) and how sensitive is the cli-mate to systematic changes in the forc-ing (climate change)? The latter isdetermined by numerous feedbackprocesses that operate to alter theexchanges of energy and water withinthe system and with the outside but, inthe truly dynamic climate system, theformer is also influenced by these sameprocesses. To learn the answers to thesequestions, therefore, we must observethe varying relationships amongst thecomponents of the climate system anddiagnose the variations of their

exchanges of energy and water todetermine how they regulate and mod-ulate the climate response to forcing.For this purpose, the observations musthave a combination of high space-timeresolution and global, long-term cover-age that can only be provided, in prac-tice, by systematic satellite observa-tions. The former is required to resolveaccurately the energy and waterexchange variations at the weather-process-level and the latter is requiredto provide enough examples of the dif-ferent possible configurations of theclimate system to understand the rangeof multi-variate, non-linear relation-ships that are produced by the interac-tions of the processes.

To describe the complete energy-water cycle requires measurements ofthe thermodynamic state of all the cli-mate components and the hydrody-namic state of the atmosphere andocean, as well as all the properties ofthem that affect the energy and waterexchanges. The state is described bythe 4-dimensional distribution of tem-perature, humidity and winds in theatmosphere, of the temperature, salini-ty and currents in the ocean and thetemperature and “water content” of theland and ice. To calculate theexchanges of energy requires determi-nation of the tendencies of the statevariables and their atmospheric andoceanic transports which are functionsof spatial derivatives of these vari-ables. Additional properties that areneeded to calculate radiativeexchanges are the gas composition ofthe atmosphere (including the maingreenhouse gases), aerosols, cloudsand surface spectral albedo/emissivity.The main additional quantities todetermine the water cycle are precipi-

Analyzing the Variations of theGlobal Ocean Energy Cycle

William B. Rossow, NASA Goddard Institute for Space StudiesJohn J. Bates, NOAA National Climatic Data Center

Yuanchong Zhang, Columbia UniversityKen Knapp, NOAA National Climatic Data Center

Ely Duenas, SSP, LLC at NASA GISSJoy Romanski, Columbia University

VARIATIONS


U.S. CLIVAR

tation (rain and snow), evaporation,water storage on the land as snow/iceand in the deep acquifer, as well aswater runoff from the land to the ocean.

The state of the ocean has beenobserved very sparsely for the pastmany decades but only recently havethese data been compiled to provide acomprehensive description of the stateand circulation of the ocean. The WorldClimate Research Program (WCRP)was established, in part, to coordinateactivities to develop a number ofdatasets that were missing for describ-ing the energy-water cycle [GARP1975]. Among the first WCRP activitieswere projects to determine the thermo-dynamic state of the world ocean (theWorld Ocean Circulation Experiment,WOCE) and to study the couplingbetween the tropical oceans and globalatmosphere (Tropical Ocean GlobalAtmosphere, TOGA). These studies arecontinuing as part of the ClimateVariations (CLIVAR) project. Severalother projects, now collected under theGlobal Energy and Water Experiment(GEWEX), have produced a collectionof cloud, precipitation, aerosol andradiative flux products that can provideimportant information about ocean-atmosphere exchanges of energy andwater (Table 1, see Rossow et al.[2006]). A newer initiative underGEWEX includes a project (SeaFlux)to determine the turbulent fluxes of heatand water at the ocean surface [Curry etal. 2004].

As one illustration of analyses thatcan be done with this set of data prod-ucts, Figure 1 shows the decadal varia-tions (anomaly relative to 1993) of the

global mean heat content of the upperocean, diagnosed from buoy and satelliteobservations (Willis et al. [2004], updat-ed, private communication), comparedwith the heat content variation inferredfrom the total surface energy fluxes,based on the GEWEX Surface RadiationBudget product (SRB, Stackhouse et al.[2001]) and the GSSTF2 turbulent flux-es [Chou et al. 2003]. Such a diagnosticapproach for the heat budget has beenadvocated by Pielke [2003]. Levitus etal. [2000] has compiled a longer recordof ocean heat content. Given the “large”uncertainties associated with these dataproducts, it is no wonder that theseresults do not yet agree but the magni-tude of the differences is much smallerthan expected. Moreover, the surfaceflux products have known sources ofuncertainty that can be worked on toimprove them; in particular the surfacelatent heat flux products based on satel-lite microwave measurements appear tohave an excessively strong increase(cooling) over this time period associat-ed with known problems of calibration.

Using six different combination-

datasets (two different surface radiativeflux products, ISCCP-FD and SRB[Stackhouse et al. 2001] and three dif-ferent surface turbulent flux products,GSSTF2, HOAPS [Grassl et al. 2000]and WHOI [Yu et al, 2004]), we canestimate the mean meridional heattransport of the global oceans (Figure2), where the error bars indicate thespread of estimates obtained from thesedifferent data combinations (cf. Zhangand Rossow [1997]). The uncertaintiesare particularly significant in the south-ern oceans and are primarily caused bydifferences among the turbulent fluxdata products (cf. Chou et al. [2004])rather than the surface radiative fluxproducts (cf. Zhang et al. [2006]).

Anomalies in the total (atmosphereplus ocean) meridional energy trans-port over the past two decades inferredfrom the ISCCP-FD reconstruction oftop-of-atmosphere radiative fluxes,which agrees very well [Zhang et al.2004] with directly inferred anomaliesat lower latitudes from ERBE [Wong etal. 2006]. The uncertainties in the sur-face fluxes currently preclude a defini-tive separation of these features intoseparate atmospheric and oceanic con-tributions, but the association withENSO events is clear, although vari-able. The higher latitude location of thetransport anomalies in 1998/99, as con-trasted with generally lower latitudeanomalies during other events, sug-gests the possibility that the formerevent was dominated by a change inatmospheric heat transport while theearlier events were dominated bychanges in oceanic heat transport. If thequality of these products can beimproved by further evaluation and

Figure 1. Comparisonof the decadal-scaleanomaly in net surfacefluxes and the varia-tions of annual upper-ocean heat content.

Figure 2. Mean merid-ional heat transport bythe global oceaninferred from six differ-ent combinations oftwo radiative flux andthree turbulent fluxproducts.


systematic re-processing, then this dif-ference could be investigated further.

To stimulate more extensive analy-ses of the variations of the global ener-gy-water cycle and the processes thatinfluence them, as well as re-process-ing of these products to improve their e l i a b i l i t y, the GEWEX RadiationPanel is organizing a complete set, atleast one dataset for each of the compo-nents of the energy-water cycle, in twoforms. The first is a summary of thedatasets in the form of monthly meanglobal maps, all in the same grid cover-ing the same time period, posted on anddownloadable from the GRP website:( h t t p : / / g r p . g i s s . n a s a . g o v / g e w e x d s e t s . h tml). The second is providing access tothe original versions of these datasets(with a variety of map grids, samplingintervals and periods covered), startingwith the four GRP products for radia-tion, precipitation, clouds and aerosols,on an active server to be hosted by

NCDC. The online summary is nowavailable and the datasets are beingassembled for the server and should beavailable by the end of in 2007. Thiscollection could form the core of a larg-er climate dataset, if datasets are addedby other components of the Wo r l dClimate Research Program such as CLI-VAR.

ReferencesChou, S-H., E. Nelkin, J. Ardizzone,

R.M. Atlas and C-L. Shie, 2003: Surface tur-bulent heat and momentum fluxes over glob-al oceans based on the Goddard satelliteretrievals, version 2 (GSSTF2). J. Climate,16, 3256-3273.

Chou, S-H., E. Nelkin, J. Ardizzone andR.M. Atlas, 2004: A comparison of latentheat fluxes over global oceans for four fluxproducts. J. Climate, 17, 3973-3989.

Curry, J.A., A. Bentamy, M.A. Bourassa,D. Bourras, M. Brunke, S. Castro, S. Chou,C.A. Clayson, W.J. Emery, L. Eymard, C.W.Fairall, M. Kubota, B. Lin, W. Perrie, R.R.R e e d e r, I.A. Renfrew, W.B. Rossow, J.

Schultz, S.R. Smith, P.J. Webster, G.A. Wickand X. Zeng, 2004: SEAFLUX. Bull. Amer.Meteor. Soc., 85, 409-424.

G A R P, 1975: The Physical Basis ofClimate and Climate Modelling, GlobalAtmospheric Research Program PublicationSeries, No. 16, pp. 265.

Grassl, H., V. Jost, R. Kumar, J. Schulz,P. Bauer and P. Schluessel, 2000: T h eH a m b u rg Ocean-Atmosphere Parametersand Fluxes from Satellite Data (HOAPS): Aclimatological atlas of satellite-derived air-sea-interaction parameters over oceans.Report No. 312, ISSN 0937-1060, MaxPlanck Institute for Meteorology, Hamburg.

Levitus, S., J.I. Antonov, T.P. Boyer andC. Stephens, 2000: Warming of the worldocean. Science, 287, 2225-2229.Pielke Sr., R., 2003: Heat storage within theearth system. Bull. Amer. Meteor. Soc., 84,331-335.

Rossow, W.B., J.J. Bates, J. Romanski,Y-C. Zhang, K. Knapp, E. Duenas, 2006:Analyzing the variations of the global ener-gy and water cycle. GEWEX NEWS, 16, 3-5.

Willis, J.K, D. Roemmich and B.Cornuelle, 2004: Interannual variability ofupper ocean heat content, temperature andthermosteric expansion on global scales. J.Geophys. Res., 109, doi10.1029/2003JC002260, (1-13).

Wong, T., B.A. Wielicki and R.B. LeeIII, 2006: Re-examination of the observeddecadal variability of earth radiation budgetusing altitude-corrected ERBE/ERBS non-scanner WFOV data. J. Climate, (in press).

Yu, L., R.A. Weller and B. Sun, 2004:Improving latent and sensible heat flux esti-mates for the Atlantic Ocean (1988-1999) bya synthesis approach. J. Climate, 17, 373-393.

Zhang, Y-C., and W.B. Rossow, 1997:Estimating meridional energy transports bythe atmospheric and oceanic general circula-tion using boundary flux data. J. Climate,10, 2358-2373.

Zhang, Y-C., W.B. Rossow, A.A. Lacis,M.I. Mishchenko and V. Oinas, 2004:Calculation of radiative fluxes from the sur-face to top-of-atmosphere based on ISCCPand other global datasets: Refinements ofthe radiative transfer model and the inputdata. J. Geophys. Res., 109, doi10.1029/2003JD004457, 1-27 + 1-25..

Zhang, Y-C., W.B. Rossow and P.W.Stackhouse, 2006: Comparison of differentglobal information sources used in surfaceradiative flux calculations: Radiative prop-erties of the near-surface atmosphere. J.Geophys. Res., 111, D13106,doi:10.1029/2005JD006873, (1-13).

VARIATIONS

Table 1. Some available global,long-term datasets that can beused to quantify variations ofthe global energy-water cycle.Most of these are being pro-duced or studied in GEWEXactivities; references and rele-vant web site addresses forthese datasets can be found onthe GEWEX Radiation Panelweb site athttp://grp.giss.nasa.gov/gewexdsets.html). Additional products(not all mentioned below) arebeing studied in CLIVAR activi-ties. Asterisks indicate datasetsto be provided on the NCDCactive server.


Subscription requests, and changes of address should be sent to the attention of the U.S. CLIVAR Office ([email protected])

U.S. CLIVAR Western Boundary Current Working Group

In January 2007, the U.S. CLIVAR WesternBoundary Current Working Group began. Aprimary objective of the working group is to

encourage better understanding of the climateimplications of the western boundary currentatmosphere-ocean interaction, which will in turnimprove the decadal and longer timescale pre-dictability of the climate system.This workinggroup topic is timely because the KuroshioExtension System Study (KESS) and CLIVARIntermediate Mode Water Dynamic Experiment(CLIMODE) groups are just beginning their analy-sis work, so the synthesis of those analyses couldbe shaped by encouraging joint group meetings.In addition, high-resolution satellite observations(with lengthening data records) and more accu-rate ocean and climate models are spurringincreased interest in the midlatitude westernboundary current regions.

The working group will seek answers to thefollowing science questions:

- How does air-sea interaction compare in thewestern North Atlantic and North Pacific? Whatare the implications of the differences? - What is the nature of atmosphere-ocean interac-

tion in western boundary current regions? Onwhat temporal and spatial scales does this occur?Is there predictability in the system? - To what extent are coupled models getting the

interaction right? Can we identify specific problems in ocean or atmosphere models? Is therea "coupled" interaction? What numerical experi-ments need to be done to test hypotheses? - To what extent does air-sea interaction extend

beyond the boundary layer and influence broaderclimate variability in both the atmosphere andocean? What role do stratiform and convectiveclouds play in the atmospheric response?

Additional information regarding theWestern Boundary Working Group can be foundat: http://www.usclivar.org/Organization/wbc-wg.html

U.S. CLIVAR OFFICE1717 Pennsylvania Avenue, NWSuite 250Washington, DC 20006

A U.S. contribution to the CLIVAR Program

U.S. CLIVAR

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