3:30 PM - 3:45 PM
[AAS03-05] Environmental Properties of Heavy Rainfall Events under Extremely Humid Conditions in Kyushu, Japan
Keywords:mesoscale meteorology, heavy rainfall, moist absolutely unstable layer (MAUL), moisture content
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. Stationary precipitating systems sometimes develop during the rainy season, which will spawn an extreme amount of rainfall, flooding, landslides, and so on. Recent studies have investigated climatological characteristics of stationary precipitating systems over the Japanese islands by using long-term datasets. During the warm season including the rainy season, a humid condition not only at low levels but also at middle levels is commonly seen. A condition that host moist absolutely unstable layers (MAULs) is sometimes seen in cases with heavy rainfalls. This study investigates the environmental conditions for the generation of extreme-rain-producing, stationary precipitating systems that recently occurred in northern Kyushu Island, Japan. It is indicated that precipitable water vapor content is extremely large as compared with the climatology of stationary precipitating systems, which is due to very humid conditions close to be saturated. Under this humid situation, MAULs appear in the lower to middle troposphere, adjacent to or as a part of stationary precipitating systems. It is also found that the volume of MAULs has a correlation with the amount of heavy rainfalls. A moist absolutely unstable condition is a state that indicates a potential for the development of convective motion. Therefore, a certain triggering mechanism is required. In the case of the July 2017 heavy rainfall case in northern Kyushu, small-scale terrain induces a convergence locally, which serves as a triggering in a moist absolutely unstable condition.