Statistical Analysis of the Occurrence Environment of Orographic Quasi-Stationary Convective Band Formed over the Eastern Part of Shikoku, Japan

Abstract

 This study statistically investigated the occurrence environment of the Muroto Line, a south–north oriented orographic quasi-stationary convective band (QSCB) that appears from the Muroto Peninsula in the eastern part of Shikoku, Japan. We objectively identified the Muroto Lines that occurred between 2004 and 2022. We focused on cases dominated by relatively shallow (Low-top case, 12 cases) and deep convective clouds (High-top case, 6 cases) and compared their occurrence environments. The results revealed similarities and differences in the occurrence environments of orographic QSCBs at different convective cloud depths.

 In all cases, tropical cyclones (TCs) were located within 1500 km west of the Muroto Lines. The Low-top cases occurred between the TC and the North Pacific Subtropical High (NPSH), which was favorable for strong southerly geostrophic winds, whereas the peripheral flow of the NPSH prevailed in Shikoku during the High-top cases. In both types, horizontal wind direction ranged from east-southeasterly to south-southeasterly near the surface and southerly above 1.5 km in height, with warm-moist and conditionally unstable thermodynamic environment. Compared to the High-top cases, the Low-top cases occurred under less conditionally unstable atmosphere, higher low- and mid-level wind speeds, larger low-level water vapor flux, and stronger vertical wind shear.