[A-CG32] Extratropical oceans and atmosphere

[ACG32-05] Interannual fluctuations of summertime heavy rainfall potentials based on two thresholds in western Japan

*Takashi Mochizuki¹ (1.Department of Earth and Planetary Sciences, Kyushu University)

Keywords:heavy rainfall potential, large ensemble simulation, Indian Ocean basin warming, Northwestern Pacific subtropical high

Heavy rainfall has recently garnered considerable attention due to changing climatic conditions. The potential amount of heavy rainfall also provides us with useful information towards discussing disaster prevention, while the potential chance of heavy rainfall has usually used so far. By analyzing a set of large-ensemble simulations using a global atmospheric model, here we demonstrated that two different physical processes in global climate variability control the interannual fluctuations of 99- and 90-percentile values of summertime daily rainfall (i.e., potential amounts) on Kyushu Island in western Japan. The 90-percentile values are closely related to large-scale horizontal moisture transport anomalies due to changes in the subtropical high in the northwestern Pacific, usually accompanied by basin-scale warming in the Indian Ocean. In contrast, tropical cyclone activity played a major role in changing the 99-percentile value. The potentials of both tropical cyclone intensity and existence density fluctuate largely owing to the sea surface temperature over broader areas of the tropical Pacific. Consequently, the potential chance of heavy rainfall represents decadal modulation due to the combined effect of these two physical processes controlling the potential amounts.