Improved simulation of the East Asian winter monsoon interannual variation by IAP/LASG AGCMs

The simulation of the East Asian winter monsoon (EAWM) has been a challenge for climate models. In this study, the performances of two versions of the AGCM developed at the IAP, versions 1 and 2 of the Grid-point Atmospheric Model of the IAP/LASG (GAMIL1 and GAMIL2), are evaluated in the context of mean state and interannual variation. Significant improvements are shown for GAMIL2 in comparison to GAMIL1. The simulated interannual variability of the EAWM, measured by the regional average of 1000 hPa meridional wind over East Asia, has evidently improved; the correlation coefficient with reanalysis data changes from 0.37 in GAMIL1 to 0.71 in GAMIL2. The associated interannual precipitation anomalies are also improved, in terms of both spatial pattern and magnitude. Analysis demonstrates that the improvements result from the better simulation of the El Nino-related Philippine Sea anticyclone (PSAC) in GAMIL2. The improved moist processes, including the stratiform condensation and evaporation in GAMIL2, lead to a reasonable atmospheric heating associated with El Nino in the tropical Pacific, which further drives the PSAC as a Rossby-wave response.