A Contrast in Precipitation Characteristics across the Baiu Front near Japan. Part I: TRMM PR Observation

Abstract

ontrasts in precipitation characteristics across the baiu front are examined with Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data near Japan during June?July (1998?2011). The vertical structure of atmospheric stratification differs between the tropics and midlatitudes. On an average, the baiu front is found around the latitude that roughly divides the midlatitude atmosphere from the tropical atmosphere. Precipitation characteristics are compared between the southern and northern sides of the reference latitude of the baiu front, which is detected with equivalent potential temperature at 1000 hPa of 345 K in terms of the boundary between the tropics and midlatitudes.The results show that there are obvious differences in precipitation characteristics between the southern and northern sides. In the south, convective rainfall ratios (CRRs) are 40%?60%, which are larger than those in the north (20%?40%). Greater rainfall intensity and taller/deeper precipitation are also observed in the south. Moreover, the characteristics of precipitation features (PFs), which are contiguous areas of nonzero rainfall, differ between the southern and northern sides. In the north, wide stratiform precipitation systems with CRRs of 0%?40% and heights of 8?11 km are dominant. In the south, organized precipitation systems with heights of 12?14 km and CRRs of 30%?50% and those with very large heights (14?17 km) and CRRs of 50%?80% are dominant in addition to wide stratiform precipitation systems. These results suggest that the mechanisms to bring rainfall are different between the southern and northern regions of the baiu front.