[A-CG36] Extratropical oceans and atmosphere

[ACG36-P02] Impact of moist air influx on short-term intense precipitation in northern Kyushu located western part of Japan during summer

*ATSUYOSHI MANDA¹, Saki Nakamuro¹, Satoshi Iizuka² (1.Mie University, 2.NIED)

Keywords:Heavy rain, Water vapor, In-tisu meteorological observation

The Kyushu region, located in the western part of Japan, often experiences heavy rainfall disasters during the summer months (June to August). Key characteristic atmospheric conditions during heavy rain events are the presence of warm, moist air masses flowing from the southwest along the fringe of the Pacific High near the sea surface, as well as moist air masses that flow from the lower to mid troposphere. While there is a long history of research into the role of these moist air masses in precipitation systems, many aspects remain unexplained. This study investigates the relationship between moisture flux flowing into the Kyushu region during the summer and short-term intense precipitation in the northern part of Kyushu, using four years of field observation data of moisture flux near the sea surface at a remote island in the East China Sea, along with atmospheric objective analysis data. Maximum 3-hour precipitation in the northern Kyushu area (P3H) was used as an index of short-term intense precipitation. The study explored the differences between large and small P3H, under conditions of relatively large moisture flux near the sea surface at the remote island. It was suggested that, in cases with large P3H, in addition to the dynamic forcing associated with synoptic and mesoscale disturbances, the increase in moisture flux near the sea surface and the moistening of the lower free troposphere are important factors. When suppression of entrainment due to moistening in the free troposphere was considered, a clear relationship was observed between convective available potential energy (ECAPE) and P3H. The influx of thick, moist air masses contributes to an increase in ECAPE, which is consistent with a recent study based on idealized numerical simulations. However, when the effects of moistening are ignored, this relationship becomes unclear. The areas of local extrema of ECAPE tend to extend from the remote island toward northern Kyushu six hours before large P3H values are observed. This suggests that operational observations at the remote island have the potential to improve forecast accuracy for intense precipitation events in northern Kyushu.