Bimodality of the South Asia High Simulated by Coupled Models

The observed South Asia High （SAH） center is characterized by two distinctive equilibrium modes during boreal midsummer, namely the center of SAH is located between 82.5°-92.5°E for the Tibetan Plateau mode and between 55°-65°E for the Iranian Plateau mode respectively. The present study describes the ability of 15 coupled general circulation models （CGCM） used in the Intergovernmental Panel on Climate Change＇s （IPCC） 4th Assessment Report to reproduce the observed bimodality of the SAH. These models reveal a wide range of skill in simulating this bimodality. Nearly half of the models reproduced the bimodality, while the other half of the models did not simulate well these two modes whereas usually preferring one mode, The models that reproduced the bimodality of the SAH present similar horizontal and vertical circulations as those features from the NCEP reanalysis data. The results from these models identify the warm characteristics of the SAH and indicate that these two modes have different dynamic and thermodynamic properties. Different characteristics of the simulated sensible heat and latent heat related to precipitation partly contribute to the difference in the simulations of the SAH bimodality. The majority of these models that prefer to simulate the Tibetan Plateau mode produce a small sensible heat flux difference between the Iranian Plateau and the Tibetan Plateau, and also generally simulate a very strong false precipitation center over the east of the Tibetan Plateau, which indicates strong latent release and thereby contributes to the preference of the SAH center on the Tibetan Plateau. Whereas, the models that reproduce the bimodality of the SAH tend to simulate large precipitation over the southern Himalayas and no obviously false precipitation is produced over the east of the Tibetan Plateau. In addition, the model＇s resolution may also have important impacts on the simulations of precipitation.