[A-AS04] Extreme Events and Mesoscale Weather: Observations and Modeling

[AAS04-05] Statistical Relationship between Summertime Precipitation and Environmental Humidity in Japan

*竹見 哲也¹、中 七海¹ (1.京都大学防災研究所)

キーワード：降水、湿潤絶対不安定層、豪雨、メソ気象学、メソ降水系

During the rainy season in Japan (i.e., Baiu season), the environmental conditions are generally very humid, with a large amount of precipitable water vapor and high relative humidity. In Naka and Takemi (2023, SOLA), it was shown that the presence of moist absolutely unstable layers (MAULs) proceeds the occurrence of heavy rainfalls and the MAUL volume correlates with the rainfall amount from case studies on recent extremely heavy rainfalls in northern Kyushu, Japan. This study conducts statistical analyses on the relationship between summertime precipitation and environmental conditions in several selected areas where rainfall amounts in summer are larger in Japan. Radar-AMeDAS analyzed precipitation products and Mesoscale Model analysis fields obtained for the time period between 2006 and 2022 are used to conduct the statistical analyses. Among the environmental conditions examined in this study, it is found that the areas with a larger amount of rainfall over the Japanese islands correspond well with those having MAULs. There are two types of environmental conditions in terms of MAULs when rainfall amounts are larger: one type appears under the presence of deep MAULs (having a thickness of greater than 0.5 km); and the other type appears when deep MAULs do not exist. In conditions with deeper MAULs the environmental humidity is extremely high, while in conditions without deep MAULs the amount of convective available potential energy (CAPE) becomes larger. Therefore, it is suggested that the presence or absence of deep MAULs will determine the type and intensity of rainfalls in summertime in Japan. It is considered that the presence and three-dimensional volume of MAULs provide useful diagnosis for the occurrence of summertime heavy rainfalls in Japan.