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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)
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
Ramstein et al. (1997) Nature
4 types of largescale 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
Kutzbach et al.
(1993)
J.Geology
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)
Mid-Holocene: 6ka
Tassili n’Ajjer, Algeria
- Sahara was greener
Paleoclimate Modeling Intercomparison
Project (PMIP)
PAGES/IGBP and WGNE/WCRP/CLIVAR
• Mechanisms of climate change
• sensitivity to model parameterizations
• Evaluation of climat models
Model-model and model-Data comparisons
• Last Glacial Maximum, 21,000 yrs BP
PMIP1 (1992-2000):
AGCM AGCM-slab
PMIP2 (2003-????):
OAGCM and OAVGCM
•
•
•
•
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 ago
same CO2 concentration as in the control run
21ka–run (Last Glacial Maximum)
orbital parameters of 21,000 years ago
CO2 concentration 200 ppm
ice sheet (Peltier 1994)
control
eccentricity 0.016724
obliquity
23.446
precession 102.04
6ka
0.018682
24.105
0.87
21ka
0.018944
22.949
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
MRI
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.
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
Jan-Feb-Mar Temperature difference (6ka–0ka) with 4 CGCMs
Zhao et al. 2004
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.
MRI
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.
LGM Precip: Observed proxy vs GCM
top
middle
bottom
pollen data
lake level data
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?
MRI
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.
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
0ka
Regression on NINO3.4 SST
6ka
Future issues
ocean
vegetation
dust
ice sheet
…