[A-CG36] Extratropical oceans and atmosphere

[ACG36-15] Impact of Sea Surface Temperature Anomalies in the East China Sea and Western Subtropical Pacific on the August 2021 Northern Kyushu Heavy Precipitation

*ATSUYOSHI MANDA¹, Terunobu Sakagami¹, Masami Nonaka², Hisashi Nakamura³, Satoshi Iizuka⁴, Qoosaku Moteki² (1.Mie University, 2.JAMSTEC, 3.The University of Tokyo, 4.NIED)

Keywords:Heavy Precipitation, Convection, Boundary layer

The effects of extratropical sea surface temperature (SST) heterogeneity on various atmospheric phenomena have received much attention recently. In this study, the effects of SST anomalies on heavy precipitation that occurred in northern Kyushu Island, Japan, in August 2021 are investigated with a convection–permitting regional atmospheric model. The mid–August SST anomalies are found to provide the following favorable conditions for the intense precipitation. Mesoscale cyclones and associated moisture fluxes intensified over a warm SST anomaly in the northern East China Sea (ECS). The vertical shear of horizontal winds also intensified over a pair of warm and cool SST anomalies in the eastern ECS. The SST anomaly in the western subtropical North Pacific affected static stability of the air parcels entering the precipitation area. The air parcels became more unstable even though they passed over the cool SST anomalies south of the precipitation area. This seemingly counterintuitive result can be explained by the stability of the atmospheric boundary layer (ABL) and the height of the air parcels. The less unstable ABL over the cool SST anomaly kept the air parcels at lower altitudes, and thus they tended to be more susceptible to the influence of heat fluxes from the sea surface and therefore becoming more unstable. The results of this study thus provide a new insight into the role of the complex SST distribution during heavy precipitation events in extratropics, suggesting the need for further studies to deepen our understanding of the atmospheric responses to the extratropical SST.