[A-CG31] Climate Variability and Predictability on Subseasonal to Centennial Timescales

[ACG31-07] Influence of intraseasonal variability on summer extreme precipitation in Japan and its climatic changes

★Invited Papers

*高橋 千陽¹、今田 由紀子²、川瀬 宏明¹ (1.気象庁気象研究所、2.東京大学大気海洋研究所)

キーワード：極端降水、夏季季節内振動、大規模アンサンブルシミュレーション

In recent years, heavy summer rainfall events have occurred frequently in various regions of Japan, and extensive damage has been reported. The development of the Boreal Summer Intraseasonal Oscillation (BSISO) has often been observed in conjunction with those record-breaking rainfall events, but the influence of BSISO on the occurrence of extreme precipitation in Japan is not well understood. Here, we quantitatively evaluate the impact of BSISO on the frequency of extreme summer precipitation in Japan for each region and further investigate the impact of global warming using large ensemble experiments with the global model MRI-AGCM and the regional climate model. As a Rossby wave train response to BSISO convective anomalies, circulation anomaly patterns and water vapor fluxes over the northwestern Pacific to East Asia are modulated, resulting in extreme precipitation on the upwind side of the Japanese mountain range. Whether the extreme precipitation is frontal or tropical cyclone origin is also found to be different by region and BSISO phase. In particular, the results show that the frequency of extreme precipitation over western Kyushu associated with BSISO has increased significantly with climate warming. It is suggested that interannual variability in tropical sea surface temperature modulates BSISO characteristics and is therefore important for the future predictability of the occurrence of heavy rainfall in a given region.