We analyzed the possible effects of recent sea surface temperature (SST) warming on the extraordinary East Asian summer monsoon (EASM) precipitation in 2020 summer. The dynamic and thermodynamic impacts of SST are examined by conducting regional climate model experiments with observed SST and cold SST where the 22-year SST trend is removed. In the presence of warm SST, precipitation increases in low latitudes but decreases in the EASM region. This dipolar precipitation change pattern opposes the precipitation anomalies in 2020 summer, indicating that the extraordinary 2020 EASM precipitation is not likely driven by recent SST warming. The warm SST suppresses the western North Pacific subtropical high expansion and weakens the southwesterly from the South China Sea toward the EASM region. In terms of large-scale atmospheric circulations, SST-induced wind changes strengthen the local Walker circulation in the South China Sea and the Philippines and the local Hadley circulation across the EASM region. These support the reduced EASM rainfall in the control experiment compared to the cold SST experiment and imply that the precipitation reduction by dynamical effects could exceed the precipitation increase by thermodynamic effects in the EASM region under warm SST.

中文翻译：

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近期海面温度变暖是否加剧了2020年东亚夏季风极端降水？


我们分析了近期海面温度（SST）变暖对2020年夏季异常东亚夏季风（EASM）降水的可能影响。通过利用观测到的海表温度和冷海表温度进行区域气候模型实验来检验海表温度的动态和热力学影响，其中去除了 22 年海表温度趋势。在温暖的海温存在下，低纬度地区降水量增加，但东亚夏季风地区降水量减少。这种偶极降水变化模式与2020年夏季降水异常相反，表明2020年东亚夏季风异常降水不太可能是由近期海温变暖驱动的。温暖的海温抑制了北太平洋西部副热带高压的扩张，削弱了南海至东亚夏季风地区的西南风。在大尺度大气环流方面，海温引起的风向变化增强了南海和菲律宾的局地沃克环流以及东亚夏季风地区的局地哈德利环流。这些结果支持了对照实验中与冷海表温度实验相比 EASM 降雨量的减少，并意味着在暖海表温度下的 EASM 地区，动力效应造成的降水减少可能超过热动力效应造成的降水增加。