EAST-ASIAN WINTER MONSOON - RESULTS FROM 8 AMIP MODELS

This study evaluates simulations of the East Asian winter monsoon in e ight GCMs that participated in the Atmospheric Model Intercomparison P roject (AMIP). In addition to validating the mean state of the winter monsoon, the cold surge and its transient properties, which includes t he frequency, intensity, preferred propagation tracks, and the evoluti on patterns of the surges, are examined. GCM simulated temporal distri bution of the Siberian high and cold surges is also discussed.:Finally , the forcing of the cold surges on the tropical surface wind and conv ection, along with their interannual variation is analysed. The mean s tate of the winter monsoon is generally portrayed well in most of the models. These include the climatological position of the Siberian high , the 200 hPa divergent center, and the large-scale wind patterns at t he surface and the 200 hPa. Models display a wide range of skill in si mulating the cold surge and its transient properties. In some of the m odels, the simulated cold surge trajectory, intensity, frequency, prop agation patterns and source regions are in general agreement with thos e from the observed. While in others, the models cannot adequately cap ture these observed characteristics. The temporal distribution of the Siberian high and cold surges were realistically reproduced in most GC Ms. Most models were able to simulate the effect of the cold surges on the tropical surface wind, although a few models unrealistically gene rated subtropical southerly wine! in the mid-winter. The relationship between cold surges and the tropical convection was not satisfactorily simulated in most models. The common discrepancies in the winter mons oon simulation can be attributed to many factors. In some models: the reason is directly related to the improper location of the large-scale convective center near the western Pacific. The satisfactory simulati ons of the monsoon circulation and the cold surges are partly due to t he topographical characteristics of the East Asian continent, i.e., th e Tibetan Plateau to the west and the oceans to the east. The correct simulation of the interannual variation of the surface wind near the S outh China Sea (SCS) and the maritime continent is a demanding task fo r most of the models. This will require adequate simulations of many a spects, including tropical convection, the Siberian cold dome, the ext ratropical-tropical linkage, and the air-sea interaction. The discrepa ncies noted here furnish a guide for the continuing improvement of the winter monsoon simulations. Improved simulations will lead to an adeq uate delineation of the surface wind and convection near the maritime continent, which is essential for portraying the winter monsoon forcin g in a coupled model.