Characteristics of quasi‐stationary band‐shaped precipitation systems in Japan between 1989 and 2022

Abstract

Abstract Quasi‐stationary band‐shaped precipitation systems (QBPSs) are the major cause of localized heavy‐rainfall events (HREs) in Japan. Using hourly radar/raingauge‐analysed precipitation amounts from 1989 to 2022, we statistically examined the occurrence characteristics of QBPSs and their associated environmental conditions. A total of 849 QBPSs were extracted during the 34‐year period, with the highest frequencies in western and southern Japan. Approximately 45% of them occurred in association with stationary fronts, and approximately 85% of them were oriented southwest–northeast or west–east. The annual occurrence frequency showed a significant increasing trend, with a regression indicating approximately a 3.4‐fold increase over the analysis period. QBPSs occurred most frequently between June and September, and their hourly frequency exhibited frequent occurrence between midnight and early morning. To elucidate the environmental characteristics favourable for QBPS formation, we analysed 225 events that occurred over Kyushu Island, western Japan, during June and July. Composite analyses using ERA5 revealed robust and coherent features: high low‐level equivalent potential temperature associated with warm and moist inflow from the East China Sea towards the Baiu frontal zone, large vertical wind shear with warm advection, synoptic‐scale ascent, low ‘level of free convection’, a deep moist layer extending into the midtroposphere, and a midlevel jet. These features were markedly pronounced relative to climatology and are consistent with previous studies on typical HREs along the Baiu frontal zone. Our results demonstrate that a combined evaluation of these environmental characteristics serves as an effective diagnostic indicator for QBPS occurrences.