[A-CG35] Multi-scale ocean-atmosphere interaction in the tropics

[ACG35-P03] Dynamic and thermodynamic contributions of ENSO to winter precipitation in Japan

*Masamichi Ohba¹, Soichiro Sugimoto¹ (1.Central Research Institute of Electric Power Industry)

Keywords:El Niño-Southern Oscillation, Precipitation, Snow, Self-organizing map, Pacific Decadal Oscillation, d4PDF

The El Niño–Southern Oscillation (ENSO) significantly affects the formation of precipitation anomalies over Japan, with more (less) and less (more) winter precipitation over the Pacific and Sea of Japan during El Niño (La Niña), respectively. In this study, the effect of ENSO on winter precipitation in Japan was investigated using a large ensemble of regional climate simulations that capture the meridional contrast of precipitation anomalies between areas facing the Sea of Japan and the Pacific along the Japanese Archipelago during ENSO. Self-organizing maps (SOMs) of the surface atmospheric circulation were applied to explore the effect of ENSO forcing on weather patterns (WPs) and associated changes in precipitation including snowfall. The results suggest that ENSO-related spatial variations in precipitation can be attributed to differences in WP frequency such as extratropical cyclone events and WP precipitation in the ENSO-modulated seasonal background state. The former and latter can be interpreted as dynamical and thermodynamic effects of ENSO, respectively. Atmospheric circulation analogs reveal that thermodynamic and dynamic effects account for approximately one-third and two-thirds of the precipitation differences between ENSO phases, respectively. ENSO–precipitation relationships in Japan are more pronounced in the negative phase of the Pacific Decadal Oscillation.