The Intermodel Diversity of East Asia’s Summer Rainfall among CMIP5 Models

Abstract

AbstractBased on the results of 46 phase 5 of the Coupled Model Intercomparison Project (CMIP5) models and empirical orthogonal function analysis, it was found that the leading diversity mode of East Asian summer rainfall across the models features a dipole structure. This structure is characterized by intensified rainfall over southern China and the area south of Japan and by weakened rainfall over northern China and explains more than 1/3 of the total intermodel variance. The uncertainty in meridional position of intertropical convergence zone (ITCZ) over the tropical North Pacific, caused by rainfall parameterization and air?sea interactions, is responsible for the mode. In models with a southward shifted ITCZ, the heating associated with inadequate rainfall (7°?18°N) over the tropical northwest Pacific excites wave activities that propagate northward and converge south of Japan in the midtroposphere. In the midtroposphere, a positive (negative) vorticity departure resides north (south) of the center of rainfall diversity. Correspondingly, the westerlies departure resides over the anomaly centers. The westerlies induce warm horizontal advection departure, leading to ascendance and rainfall variability.In addition, the rainfall diversity south of Japan induces changes in rainfall over northern China; this, in turn, promotes rainfall over the area south of Japan. Anomalous positive latent heating associated with the rainfall south of Japan induces anomalous northerlies and northeasterlies over northern China. This phenomenon depresses rainfall in northern China through bringing in dry air and weakening evaporation. This rainfall excites an upper-troposphere vorticity departure to the west, exciting wave activity propagating southeastward and downward. In the midtroposphere, the waves converge south of Japan and reinforce the westerlies and the rainfall diversity there.