Simulating Multi-Season Past Droughts
Abstract

Abstract Author: Hongmei Li, Aiguo Dai, Tianjun Zhou, and Jian Lu

Abstract Title: Responses of East Asian Summer Monsoon to Historical SST and Atmospheric Forcing During 1950-2000

Abstract: The East Asian summer monsoon (EASM) circulation and summer rainall over East China have experienced large decadal changes during the latter half of the 20th century. To invesgate what have caused these changes, a series of simulations using the National Center for Atmospheric Research (NCAR) Community Atmospheric Model version 3 (CAM3) and the Geophysical Fluid Dynamics Laboratory (GFDL) Atmospheric Model version 2.1 (AM2.1) are analyzed. These simulations are forced separately with different historical forcing, namely tropical sea surface temperature (SSTs), global SSTs, greenhouse gases plus aerosols, and a combination of global SSTs and greenhouse gases plus aerosols. This study focuses on the relative roles of these individual forcings in causing the observed monsoon and rainfall changes over East Asia during 1950-2000. The simulations from both models show that the SST forcing, primarily from the Tropics, is able to induce most of the observed weakening of the EASM circulation; while the greenhouse gas plus (direct) aerosol forcing increases the land-sea thermal contrast and thus enhances the EASM circulation. The results suggest that the recent warming in the Tropics is a primary cause for the weakening of the EASM since the late 1970s. However, a realistic simulation of the relatively small-scale rainfall change pattern over East China remains a challenge for the global models.