[A-CG43] Multi-scale ocean-atmosphere interaction in the tropics

[ACG43-09] Relationship between regional heavy rainfall in Japan and
interannual to decadal variability in the Pacific Ocean.

*野末 剛史¹、今田 由紀子¹ (1.東京大学大気海洋研究所)

キーワード：極端降水、熱帯太平洋十年規模変動、エルニーニョ、ラニーニャ、台風

This study investigates the relationship between heavy regional rainfall events in Japan and sea surface temperature (SST) variabilities in the Pacific Ocean at different timescales. For this purpose, the large-ensemble database so-called d4PDF (Database for Policy Decision making for Future climate change) was analyzed, which consists of 100-member simulations for each of the 60-km atmospheric general circulation model (AGCM) and high-resolution downscaled products with a 20-km non-hydrostatic regional climate model (RCM). The index of regional heavy rainfall frequency over specified regions of Japan in each month was decomposed into high-frequency (interannual) and low-frequency (inter-decadal to long-term trend) components to distinguish the contributions of SST variabilities at different timescales. SST anomalies regressed onto each rainfall index revealed distinct features. For the eastern Kyushu region, in July, the high-frequency component was associated with warm anomalies in the central tropical Pacific, while the low-frequency component showed a pattern similar to the tropical Pacific decadal variability (TPDV). The impacts of typhoons were evident in both timescales. Further analyses showed that density of typhoons approaching western Japan was related to central Pacific (CP) ENSO on interannual timescale, and TPDV on interdecadal timescale. These features were particularly strong in July. In other typhoon months, the low-frequency component of the heavy rainfall index was weakened, and the increase in such typhoons associated with TPDV was weak or undetectable. This study indicates that heavy regional rainfall in Japan is affected by different SST variabilities in the Pacific Ocean at different time scales.