Diversity in the Orientation of Linear-Stationary type Heavy Rainfall Events in the Tohoku Region, Japan and Associated Synoptic-Scale Atmospheric Circulations

Abstract We investigated the characteristics of the synoptic-scale atmospheric circulation in linear-stationary heavy rainfall areas (LS-HRAs) in the Tohoku region, Japan. Of the 58 identified events, more than 70% (42 cases) occurred on the Sea of Japan side. We classified them into three orientation-based groups—southwest–northeast (SW–NE) type; west–east (W–E) type; northwest–southeast (NW–SE) type and performed composite analysis for each group. In the lower troposphere, anomalous water vapor flows into the Tohoku region due to the synoptic-scale high- and low-pressure systems. Particularly, the locations of the low-pressure systems associated with the SW–NE and NW–SE types were noticeably different: for the SW–NE type, the cores were located off the west coast of the Tohoku region, whereas for the NW–SE type, they were located off the east coast. In the middle troposphere, jet streams that were strongly associated with high- and low-pressure systems were found above the Tohoku region. Furthermore, the spatial patterns of these cyclonic and anticyclonic systems played a critical role in determining the orientations of the LS-HRAs, with a correlation of about 0.85 between the orientation of the LS-HRAs and the wind direction.