Spatiotemporal distribution of precipitation related to weakening of tropical cyclones in Korea

In this study, we analysed the spatiotemporal characteristics of precipitation in Korea in connection with weakening of tropical cyclones (TCs) around the Korean Peninsula (32°-36° N, 122°-132° E) over the past 30 years (1979-2015). Weakened TCs were classified into two categories: TCs weakened to extratropical cyclones (WEC) and TCs weakened to tropical depressions (WTD). In WEC, precipitation was evenly distributed over all of the Korean Peninsula, with the greatest precipitation recorded on the southern coast. In WTD, the amount of precipitation was the greatest on the southern coast, while low precipitation was recorded in the central and inland areas of Korea. In Region 1 (Central Province, Jeollabuk-do, and the inland region of Gyeongsangbuk-do), greater precipitation was observed in WEC than in WTD. In Region 2 (Jeollanam-do, Gyeongsangnam-do, Southeast Gyeongsangbuk-do, and Jeju-do), little difference in precipitation was found between WEC and WTD. In WEC, potential vorticity developed in the upper-level troposphere with TCs approaching Korea along with a thermal trough in the lower-level troposphere to the northwest of the TCs. Meanwhile, an upper-level troposphere jet and a strong upper-level troposphere divergence region were observed to the northeast of the TCs. It was assumed that these meteorological factors had induced baroclinic disturbance and nondiabatic process, creating a wide precipitation area around the TCs. In contrast, in WTD, none of the intense potential vorticity, thermal trough, and upper-level troposphere jet was observed around the TCs. Consequently, only a narrow precipitation area was created around the TCs. The upper-level troposphere divergence region was relatively small, and no intense precipitation area was formed around the TCs.