[A-AS08] General Meteorology

[AAS08-P12] Impacts of Regional SST Warming Patterns on Precipitation and Circulation Changes in the Western North Pacific

*Chao-An Chen¹, Huang-Hsiung Hsu², Hsin-Chien Liang², Yu-Len Chen², Ping-Gin Chiu³, Chia-Ying Tu² (1.National Science and Technology Center for Disaster Reduction, Taiwan , 2.Research Center for Environmental Changes, Academia Sinica, Taiwan, 3.Geophysical Institute, University of Bergen, Norway)

Keywords:Western North Pacific, SST warming pattern, circulation, precipitation

The Western North Pacific (WNP) area is the region known for its active convection and typhoon activity in the boreal summer. Whereas future climate changes in the WNP remain certain degree of uncertainty, this study aims to explore how the future SST warmings in various ocean basins might influence WNP circulation and precipitation by conducting a series of numerical experiments using the high-resolution Atmospheric General Circulation Model (HiRAM), forced by global and regional SST warming (SST’spa). A decreased precipitation and anomalous anticyclonic circulation in the WNP region are shown in HiRAM global warming simulation (RCP8.5_Ens). This study found that the anticyclonic circulation associated with WNP subtropical high can be strengthened by SST’spa in various basins, such as the Indian Ocean, tropical Atlantic, subtropical northeastern Pacific where the PMM prevails, and the entire tropical ocean belt. These experiments display similar responses with decreased precipitation, anomalous anticyclonic circulation in prevailing convective regions, and anomalous convergence in the upper-tropospheric divergence region. These cases mostly reproduce the WNP response in HiRAM RCP8.5_Ens, indicating that most SST’spa can lead to decreased precipitation and enhanced WNP subtropical high. In contrast, the SST’spa in the WNP and equatorial eastern Pacific display opposite response and mixed effects to RCP8.5_Ens, respectively, tending to weakly offset the dominant influences of remote ocean warming. Contrasted responses are also detected in typhoon activity changes. This study suggests that the WNP, being the epicenter of the global teleconnection of divergent and rotational flow, is susceptible to the SST contrast between the WNP and remote ocean basins. That is, a smaller contrast would weaken the circulation, convection, and TC activity in the WNP. These findings imply a high probability of decreased precipitation and enhanced subtropical high in the WNP in the warmer future. Although this study does not consider atmosphere-ocean interactions that might weaken or enhance the results, the findings could contribute to the understanding of how future global ocean warming could impact the WNP climate.