Interdecadal variation of precipitation days in August in the Korean Peninsula

The present study examines a climate regime shift in the time series of the number of rainy days during August in the Korean Peninsula. The statistical change-point analysis indicates that a significant shift occurred in the time series around 1998, providing a rationale to divide it into two parts: 1975-1997 for the shorter rainy-day period and 1998-2012 for the longer rainy-day period. To examine the cause of recent rapid increases in the number of days with precipitation in August in the Korean Peninsula, differences in the averages of large-scale environments between the 1998-2012 period and the 1975-1997 period were analyzed. The differences in stream flows showed that anomalous cyclones were reinforced in the East Asian continent while anomalous anticyclones were reinforced in the western North Pacific at all layers of the troposphere. The anomalous anticyclones reinforced in the western North Pacific were associated with the western North Pacific subtropical high (WNPSH) developed a little more toward the Korean Peninsula recently. Consequently, the Korean Peninsula has been affected by anomalous south westerlies that supplied warm and humid airs from low tropical regions to the Korean Peninsula. The vertical thermal instability (warm anomaly at lower-level and cold anomaly at middle and upper-level) developed near the Korean Peninsula. In addition, upper tropospheric jets were reinforced further recently near the Korean Peninsula to provide good environments for development of upward flows. The frequency of TCs that affect the Korean Peninsula in August also increased rapidly since 1998. (C) 2016 Published by Elsevier B.V.