Evaluation, Reconstruction And Projection Of Summer Atmospheric Circulation Over East Asia By IPCC AR4 Climate Models

Based on European Center for Medium range Weather Forecasting (ECMWF) 40-year reanalysis data (ERA40), evaluated are the capabilities of 21 Coupled Ocean-Atmosphere General Circulation Models (CGCMs) from Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4) firstly. Then do analysis on the reconstruction capability of superensumble using 14 relatively well climate models to simulate SLP,850hpa wind,500hPa geopotential height, atmospheric general circulations in East Asia and East Asian summer monsoon. Finally the future change of East Asian monsoon is estimated under IPCC A1B scenario. Results as following:(1) The basic spatial patterns of the climatology of SLP, U, V wind and 500hPa geopotential height are well captured, The correlations all above 0.64; On the whole, the simulation of 500hPa potential height is the best, exclude GISS_EH, The correlation coefficients all greater than 0.96, there are no obvious differences in the simulated 500hPa geopotential height; but the simulation of SLP is relatively poor, The simulated SLP exhibits evident deficiency; Most of the models can simulate 850hPa U, V wind very well. On the whole, the simulated climatology of India Low Pressure systems and western Pacific subtropical high are weaker than ERA40, and the simulated western Pacific subtropical high is systematically weaker than the observation.(2) On the whole, the abilities of the models to simulate the interannual variabilities of different climate elements are poor; The simulation of 500hPa geopotential height is better than those of SLP and 850hPa wind;As far as the two main circulation systems over East Asia, the simulation of India Low Pressure Trough is better than India Low Pressure;the capability of the models to simulate the intensity and location of the subtropical High is stronger than that in India Low Pressure system; Most models can simulate the enhanced trend of the subtropical high well after the end of 1970's; From the evaluation of selected monsoon indexes, it is found that the performances of most models in simulating interannual variability of the circulation anomalous indexes are better than the indexes based on the the land-sea pressure difference and the meridional wind.(3) The performance is significant increased when superensumble method is used to reconstruct sea level pressure, wind,500hPa geopotential height based on 14 relatively well models;The reconstruction of main atmospheric general circulations in East Asia and three East Asian monsoon indexes using 14 climate models indicate that the superensumble can well rebuild variability of the East Asian atmospheric general circulations in time and space and East Asian monsoon trend over the past 40 years.(4) The 2010-2099 monsoon indexes is prediction using superensumble method base on 14 climate models, The results show that the weak trend of East Asia summer monsoon may continue to 2025,then it will increase. Anomalies of sea level pressure and 850hpa wind relative to 1970-1999 during typical strong and weak monsoon Period is also consistent with the monsoon index.