Response of the East Asian summer monsoon to doubled atmospheric CO2: Coupled climate model simulations and projections under IPCC AR4 |
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Authors: | R H Kripalani J H Oh H S Chaudhari |
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Institution: | (1) Integrated Climate System Modeling Laboratory, Department of Environmental and Atmospheric Sciences, Pukyong National University, Busan, South Korea;(2) Indian Institute of Tropical Meteorology, Pune, India |
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Abstract: | Summary The East Asian (China, Korea and Japan) summer monsoon precipitation and its variability are examined from the outputs of
the coupled climate models performing coordinated experiments leading to the Intergovernmental Panel on Climate Change Fourth
Assessment Report (IPCC AR4). Out of the 22 models examined, 14 reproduce the observed shape of the annual cycle well with
peak during the boreal summer (June through August), but with varying magnitude. Three models simulate the maximum a month
later and with lower magnitudes. Only one model considerably underestimates the magnitude of the annual cycle. The remaining
4 models show some deviations from the observed. Models are unable to simulate the minimum in July with peaks in June and
August associated with northward shifts of the Meiyu-Changma-Baiu precipitation band. The realistic simulation of the annual cycle does not appear to depend on the model resolution. The inter-model
variation is slightly larger during summer, implying larger diversity of the models in simulating summer monsoon precipitation.
The spatial rainfall patterns are reasonably well simulated by most of the models, with several models able to simulate the
precipitation associated with the Meiyu-Changma-Baiu frontal zone and that associated with the location of the subtropical high over the north Pacific. Simulated spatial distribution
could be sensitive to model resolution as evidenced by two versions of MIROC3.2 model. The multi-model ensemble (MME) pattern
reveals an underestimation of seasonal precipitation over the east coast of China, Korea-Japan peninsular and the adjoining
oceanic regions. This may be related with the mass-flux based scheme employed for convective parameterization by majority
of the models. Further the inter-model variation of precipitation is about 2 times stronger south of 30° N, than north of
this latitude, indicating larger diversity of the coupled models in simulating low latitude precipitation. The simulated inter-annual
variability is estimated by computing the mean summer monsoon seasonal rainfall and the coefficient of variability (CV). In
general the mean observed seasonal precipitation of 542 mm and CV of 6.7% is very well simulated by most of the models. Except
for one model mean seasonal precipitation varies from 400 to 650 mm. However the CV varies from 2 to 9%.
Future projections under the radiative forcing of doubled CO2 scenario are examined for individual models and by the MME technique. Changes in mean precipitation and variability are tested
by the t-test and F-ratio respectively to evaluate their statistical significance. The changes in mean precipitation vary from −0.6% (CNRM-CM3)
to about 14% (ECHO-G; UKMO-HadCM3). The MME technique reveals an increase varying from 5 to 10%, with an average of 7.8% (greater
than the observed CV of 6.7%) over the East Asian region. However the increases are significant over the Korea-Japan peninsula
and the adjoining north China region only. The increases may be attributed to the projected intensification of the subtropical
high, Meiyu-Changma-Baiu frontal zone and the associated influx of moist air from the Pacific inland. The projected changes in the amount of precipitation
are directly proportional to the projected changes in the strength of the subtropical high. Further the MME suggests a possible
increase in the length of the summer monsoon precipitation period from late spring through early autumn. The changes in precipitation
could be stabilized by controlling the CO2 emissions. |
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