Modeling of paleo-monsoon

Akio KITOH

Meteorological Research Institute, Japan Meteorological Agency

1: Use of paleo-climate modeling

2: 6ka (Mid-Holocene)

3: 21ka (Last Glacial Maximum)

Ramstein et al. (1997) Nature

Orogeny, plate motion and land-sea distribution

Uplift of the Himalayan/ Tibetan plateau and the retreat of the Paratethys played important role in driving the Asian monsoon changes

Kutzbach et al. (1993) J.Geology

4 types of large-scale forcing or b.c. for the South Asian monsoon

the monsoon is most sensitive to the elevation and radiation (orbital) changes

CCM1+50m mixed-layer

Use of paleo climate modeling

Snapshot simulations of past climates by climate models can be very useful to investigate the physical mechanisms of climate change. They can be used for example to test the sensitivity of the climate system to supposed forcing of past climates such as variations in solar radiation, ice sheet extent or CO2.

Use of paleo climate modeling (cont)

Past climate simulations also allow us to test the simulated climate sensitivity. AGCM parameterizations are developed and validated by using present-day observations. However, current data cannot ensure that these parameterizations will produce a correct sensitivity of the climate. Past climates offer a unique opportunity to test model results in this respect, at least when sufficiently quantitative and globally distributed paleo-data are available and when the causes of the changes are deterministic and well quantified.

Last Glacial Maximum: 21ka

Dome Concordia (Antarctica): 740,000 years of climate change

(EPICA Members, 2004)

Tassili n’Ajjer, Algeria - Sahara was greener

Mid-Holocene: 6ka

Paleoclimate Modeling Intercomparison Project (PMIP)Paleoclimate Modeling Intercomparison Project (PMIP)

PAGES/IGBP and WGNE/WCRP/CLIVAR

• Mechanisms of climate change• sensitivity to model parameterizations• Evaluation of climat models

PMIP1 (1992-2000):AGCM AGCM-slab

Model-model and model-Data comparisons

PMIP2 (2003-????): OAGCM and OAVGCM

• Last Glacial Maximum, 21,000 yrs BP

• Mid-Holocene, 6000 yrs BP• Early Holocene• Last glacial inception• Water hosing (CMIP/PMIP)

http://www-lsce.cea.fr/pmip2

PMIP data: vegetation map

PMIP data: tropical water balance at LGM

plant-available moisture

runoff (equivalent to precipitation minus evaporation)

PMIP data: global lake status

PMIP data: diagnostic for mid-holocene precipitation over Northern Africa

Experiment

Control run

6ka–run (mid-Holocene)orbital parameters of 6,000 years agosame CO2 concentration as in the control run

21ka–run (Last Glacial Maximum)orbital parameters of 21,000 years agoCO2 concentration 200 ppmice sheet (Peltier 1994)

control 6ka 21kaeccentricity 0.016724 0.018682 0.018944obliquity 23.446 24.105 22.949precession 102.04 0.87 114.42

6,000 yr BP monsoon

mid-Holocene

Insolation at present and 6,000 years ago

In the NH, insolation was larger in summer and less in winter. Annual mean insolation anomaly was positive in high latitudes, and was negative, about –1 W/m2, in the tropics.

TOA insolation difference at 6ka and 21ka

Note the different scale.

The 6ka has a larger seasonal variation with negative anomaly in NH winter and positive in NH summer.

In the tropics, annual mean difference is -1 W/m2 in 6ka and +1 W/m2 in 21ka.

Mid-Holocene climate

# The Afro-Asian summer monsoon was stronger and shifted northward

# Weaker and less frequent ENSO activity

# SSTs in the western Pacific were about 1oC warmer and rainfall was less variable

- more La Nina like state in the mean

6ka JJA Surface Temp, Precip, Wind

Afro-Asian monsoon shifts northward. Negative ground temp.

Easterly wind anom in the Western Pacific (stronger Walker). La Nina type.

MRI

6ka DJF Surface Temp, Precip, Wind

Strong Asian winter monsoon. Annual mean SST 0.35C decrease.

MRI

PMIP

Following the insolation change, all PMIP models simulate an increased seasonal cycle of temperature over the continents of the northern hemisphere, reaching about +/-1C on global average for the winter/summer seasons.

PMIP

The summer warming reaches a maximum between 40N and 50N with more than 2C, whereas the cooling occurs further south, between 0N and 30N, with a similar magnitude.

6ka GCM comparison

N Africa Precip

• Models do not reproduce precipitation to maintain steppe climate

• Importance of air-sea interaction and vegetation feedback

Zhao et al. 2004

Jan-Feb-Mar Temperature difference (6ka–0ka) with 4 CGCMs

Jul-Aug-Sep Temperature difference (6ka–0ka) with 4 CGCMs

Zhao et al. 2004

Jul-Aug-Sep Precipitation difference (6ka–0ka) with 4 CGCMs

Zhao et al. 2004

Jul-Aug-Sep 850hPa wind difference (6ka–0ka) with 4 CGCMs

Zhao et al. 2004

6ka precipitation anomalies over northern Africa (20W-30E) by AGCM and CGCM

Maximum precip: 10-15N in AGCM 10-18N in CGCM

21,000 yr BP monsoon

Last Glacial Maximum

Insolation at present and 21,000 years ago

PMIP

An annual mean global cooling of about 4C is obtained by all the models forced by the CLIMAP SST estimates. The range of cooling is larger when using computed SSTs, from –6C to –2C, since models are no longer constrained by the same change in SST.

PMIP

Compared to the fixed SST experiments, computed SST experiments produce a greater inter-hemispheric difference with a weaker cooling in the southern hemisphere due to less sea ice extent than prescribed by CLIMAP. In the tropics, computed SSTs are colder than CLIMAP, especially over the tropical Pacific where the warm pools of CLIMAP are not reproduced.

PMIP

According to both sets of PMIP simulations, the LGM climate is also more arid over most of the northern continents and in the tropics. At the regional scale, the simulations are characterized by a number of common features, including a reduction in the strength of the Afro-Asian monsoon and increased intertropical aridity.

21ka annual mean SST: CLIMAP vs GCM

Large decrease in high latitudes.

East-west contrast in the tropics, larger decrease in the Caribbean.

Positive SST anomaly in the subtropical Pacific.

MRI

LGM Precip: Observed proxy vs GCMtop pollen data

middle lake level data

bottom GCM (P - E)

Farrera et al. 1999 Clim Dyn

MRI

・ How does the climate model project as a future climate?

・ Can we use the past warm-day climate as a proxy of the future climate?

JJA Precipitation & 850hPa Winds

Northward shift of monsoon westerly and intensified rainfall over the Afro-Asian summer monsoon region.

Easterly anomaly over the western tropical Pacific associated with strengthened subtropical anticyclones.

MRI

JJA Precipitation: CO2 vs 6ka

Overall resemblance.

In the 6ka run, a northward shift of the Afro-Asian monsoon rainfall belt is more pronounced with a decrease over the ocean south of India.

MRI

JJA 850hPa Winds: CO2 vs 6ka

Also similar each other.

There is a northward shift of monsoon westerly around India, easterly anomaly in the western Pacific, westerly anomaly around Japan, and westerly anomaly in the equatorial eastern Pacific.

MRI

JJA Surface Temperature: CO2 vs 6ka

The CO2 run shows an overall increase with its maximum in the 40 deg latitude. There is a mimimum over the monsoon rain belt due to increased rainfall.

In the 6ka run, temperature increases in the northern continent. The monsoon rain belt corresponds to negative temperature anomaly. SST lower about 0.4 deg C.

MRI

Paleo-ENSO

A long term record of Oxygen-18 isotope data from corals in the western Indian Ocean off Kenya compared against the COADS SST record for recent years.

From CLIVAR web-site

Coral records show weaker and less frequent ENSO activity in mid-Holocene. SSTs in the western tropical Pacific was about 1 deg warmer and rainfall was less variable, suggesting a more La Nina like mean state.

ENSO Reconstruction

Control run: global SST EOF1 and regressions

6ka run: global SST EOF1 and regressions

Power spectrum of NINO3.4 SST and SST EOF1

Regression on NINO3.4 SST0ka 6ka

Future issues

oceanvegetationdustice sheet…