Abstract
The changes of the East Asian summer monsoon (EASM) in response to increased CO2 atmospheric forcing are analyzed using the Super-Parameterized Community Climate System Model version 4 (SP-CCSM4). In response to the global warming caused by the increased atmospheric CO2 concentration, the precipitation and circulation of the EASM intensify. These changes are explained by the westward extension of the western North Pacific subtropical high (WNPSH). The displacement of the WNPSH is caused by two mechanisms: (i) the increase of sea surface temperature and (ii) the reduction of latent heat flux over the South China Sea and adjacent western Pacific Ocean. The changes in the surface fluxes over the tropics induce a Gill-type anticyclonic circulation in the lower troposphere to the north of the heating anomaly and a Rossby wave train from the tropics into the mid-latitude Pacific Ocean. The westerly anomalies on the northern side of the anticyclone strengthen the southwesterly flow on the western edge of the WNPSH. This flow further affects the wind anomalies and moisture transport over East Asia. The Rossby wave train affects the large-scale circulation associated with the WNPSH.
Highlights
The East Asian summer monsoon (EASM) is an important component of the global monsoon system (He et al 2007) and the Asian climate system (Tao and Chen 1987)
The uncoupled simulations project a positive trend of EASM precipitation, and the increase is slightly higher than in the simulation with fully interactive air-sea interactions
The EASM response to global warming tends to be dominated by changes in surface conditions and is sensitive to the remote influence of changes in the air-sea interactions in the deep tropics (15° S–15° N)
Summary
The East Asian summer monsoon (EASM) is an important component of the global monsoon system (He et al 2007) and the Asian climate system (Tao and Chen 1987). The impacts of changes induced by global warming in the South China Sea (SCS) and western Pacific Ocean (WP) onto the EASM are not completely understood These regions play an important role in moisture transport for EASM precipitation (Ding et al 2005). This simulation captures the slow adjustment of atmosphere to the increase of CO2 concentration through the SST influence Analysis of these simulations suggest that surface heat fluxes over SCS and WP induced by the global warming explain the changes in EASM precipitation associated with the global warming caused by the quadrupling of atmospheric CO2. Two more AMIP-type experiments are conducted to establish the sensitivity of EASM precipitation to the remote influence over SCS and WP regions These sensitivity-type experiments are discussed in Section 3 along with the mechanisms on how and why changes in the surface heat fluxes over SCS and WP induced by the global warming affect EASM precipitation.
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