[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

*Chiharu Takahashi¹, Yukiko Imada², Hiroaki Kawase¹ (1.Meteorological Research Institute Japan Meteorological Agency , 2.Atmosphere and Ocean Research Institude, The University of Tokyo)

Keywords:extreme precipitation, Boreal Summer Intraseasonal Oscillation, large ensemble simulation

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.