A Statistical Study on Senjo-Kousuitai in a Regional Reanalysis for Japan (RRJ-Conv)

Abstract

The mesoscale heavy rainfall, “Senjo-Kousuitai” (SK), often causes severe disasters. This study utilizes a regional reanalysis dataset for Japan (RRJ-Conv; hourly data from 1976 to 2020 with a horizontal resolution of 5 km) to extract and analyze SK events across Japan and its surrounding area. By applying an objective extraction method, we identified 6760 SK events. They are mostly oriented southwest–northeast or west–east and more frequently appear between June and October and in the morning. These characteristics of their occurrences agree with those in observations. While RRJ-Conv does not reproduce all observed SK events, the vast number of SK samples is useful for statistical analysis of their characteristics and environmental conditions. The present study demonstrates that the SK orientations have the strongest correlation with wind directions at 600 hPa with a slight clockwise deviation from the wind direction at this altitude. The environmental winds exhibit veering, whose magnitude decreases after onsets of SK.