Response of the East Asian Summer Monsoon to Atmospheric CO2 Forcing and Subsequent Sea Surface Warming

Abstract:

The East Asian summer monsoon (EASM) is one prominent summertime circulation feature, arising from zonally asymmetric forcing, such as land-sea contrast, topographic influences and sea surface temperature (SST) patterns. In this study, we investigate the EASM regional climate change at different time scales in the Coupled Model Intercomparison Project – Phase 5 (CMIP5) archive. In the greenhouse gas forced scenario, the reduction of radiative cooling and the increase in continental surface temperature occur much more rapidly than changes in SSTs. On shorter time scales, before SSTs are able to adjust, the rainfall in the monsoon region decreases (increases) over ocean (land) in most models. On longer time scales, as SSTs increase, rainfall changes have opposite sign. The total response to atmospheric CO2 forcing and subsequent SST warming is a large (modest) increase in rainfall over ocean (land) in the EASM region. Dynamic changes, in spite of significant contributions from the thermodynamic component, play an important role in setting up the spatial pattern of the precipitation response. Rainfall anomalies over East China are a direct consequence of local land-sea contrast, while changes in the broader rainfall band over the ocean are closely associated with the displacement of the larger-scale North Pacific Subtropical High. Numerical simulations with the GFDL AM2.1 GCM show that topography and SST patterns play an important role in rainfall changes in the EASM region.