East Asian winter monsoon: results from eight AMIP models

This study evaluates simulations of the East Asian winter monsoon in eight GCMs that participated in the Atmospheric Model Intercomparison Project (AMIP). In addition to validating the mean state of the winter monsoon, the cold surge and its transient properties, which includes the frequency, intensity, preferred propagation tracks, and the evolution patterns of the surges, are examined. GCM simulated temporal distribution of the Siberian high and cold surges is also discussed. Finally, the forcing of the cold surges on the tropical surface wind and convection, along with their interannual variation is analyzed. The mean state 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 the surface and the 200 hPa. Models display a wide range of skill in simulating the cold surge and its transient properties. In some of the models, the simulated cold surge trajectory, intensity, frequency, propagation patterns and source regions are in general agreement with those from the observed. While in others, the models cannot adequately capture these observed characteristics. The temporal distribution of the Siberian high and cold surges were realistically reproduced in most GCMs. Most models were able to simulate the effect of the cold surges on the tropical surface wind, although a few models unrealistically generated subtropical southerly wind 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 monsoon 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 simulations of the monsoon circulation and the cold surges are partly due to the topographical characteristics of the East Asian continent, i.e., the Tibetan Plateau to the west and the oceans to the east. The correct simulation of the interannual variation of the surface wind near the South China Sea (SCS) and the maritime continent is a demanding task for most of the models. This will require adequate simulations of many aspects, including tropical convection, the Siberian cold dome, the extratropical-tropical linkage, and the air-sea interaction. The discrepancies noted here furnish a guide for the continuing improvement of the winter monsoon simulations. Improved simulations will lead to an adequate delineation of the surface wind and convection near the maritime continent, which is essential for portraying the winter monsoon forcing in a coupled model.