Meso- and Small-scale Structures of a Cold-frontal Precipitation System Affected by a Small Low and Mesoscale Orography

Abstract

   A cold-frontal precipitation system which passed over the Kanto district was studied using surface observation data at meteorological observatories and AMEDAS stations, and those by the Tsukuba radar. The precipitation system was found to be affected by a small low and by mesoscale orography to the west of Kanto. The small low which was originally associated with a short-wave trough below 500 mb was enhanced by surface heating. As the low developed, it organized warm southerly winds which were responsible for active convections near the surface cold front. Convective clouds occurred near the surface cold front, moved to the cold air side, and dissipated over the cold air. After the low passed the Kanto district, the southerly winds over the district disappeared and the convective rain near the surface cold front stopped.
   During the passage of the cold front over the central part of the Japan Islands, the cold air behind the front was dammed up by the mesoscale orography and went round. The advance of the surface cold front over the Kanto district was slower than that to the north and to the southwest of the district.