How well do climate models simulate regional atmospheric circulation over East Asia?

This study presents a comprehensive and quantitative evaluation of the mean state of summer atmospheric circulation over East Asia. Attention is paid to the South Asian high (SAH), western North Pacific subtropical high (WNPSH) and Indian low (IL) at the upper, middle and lower troposphere, respectively. A total of 31 state-of-the-art climate models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) are used as examples for the analysis. Most models can basically simulate the three closed-circulation systems (CCSs), although there is a certain inter-model spread and an underestimation of their intensity. In terms of geographic location, models demonstrated the best performance for SAH and the poorest performance for WNPSH. The latter shows a generally south-westward shift compared to the National Centers for Environmental Prediction (NCEP) reanalysis. Five atmospheric fields (zonal and meridional wind at 850 hPa, geopotential height at 500 and 100 hPa and sea level pressure) are inspected and generally well reproduced in models, with Taylor-S indices all larger than 0.84 for 90% of the models. The best performance is for the geopotential height of 500 hPa with an average Taylor-S index of 0.98. Models' skill in simulating the sea level pressure is the lowest. However, a significant positive correlation with models' resolution is observed. Almost all models underestimate the 100 hPa geopotential height over East Asia, mainly due to the common cold bias in the troposphere. As a whole, CCSM4, CNRM-CM5, CESM1-CAM5 and NorESM1-M are identified as high-skill models for simulating the East Asian atmospheric circulation. High-skill models also show better simulation of precipitations in East China, with a 21.3% decrease of dry biases in Southeast China. The physical explanation for this linkage is also reported to reside in the central position of the WNPSH, which determines the quality of 850 hPa winds and water vapour transport in Southeast China.