Changes in tropical cyclone activity that has affected Korea since 1999

Abstract

This study investigated the annual frequencies of tropical cyclones (TCs) that affected Korea during summer (June–September) over the last 60 years. Using a statistical change-point analysis, we found that significant regime shifts occurred in 1999 and 2005, as well as in the mid-1960s and mid-1980s. Focusing on the recent TC activities, this study analyzed the differences between the high-frequency period from 1999 to 2004 (P1) and the low-frequency period from 2005 to 2010 (P2). The analysis reveals that TCs during P2 tended to occur, move, and recurve farther to the west in the western North Pacific (WNP). This is because the WNP high expanded farther to the west during P2 compared to P1; as a result, more TCs made landfall on the west coast of the Korean peninsula (KP) during P2. In contrast, during P1, TCs tended to make landfall more frequently on the south coast of the KP. This implies that the recent TC tracks landing on the KP shifted gradually to the northwest. The analysis of streamlines at 500 hPa show that an anomalous northerly strengthened in the KP due to the formation of an anomalous anticyclone and an anomalous cyclone to the west and east of the KP, respectively. These anomalies played a role in blocking TCs from moving to the KP. At 850 hPa, the anomalous anticyclonic circulation was strengthened in most of WNP. This circulation formed an unfavorable environment for TC genesis, reducing the TC genesis frequency during P2. We verified this low convective activity in the WNP during P2 by analyzing the outgoing longwave radiation, vertical wind shear, and sea surface temperature.