Abrupt Decrease of Wintertime Cold Nights in Korea in the Late 1980s

Abstract

The decadal change of wintertime cold nights in Korea and its relationship with atmospheric circulation are investigated. Wintertime cold nights, defined as the nights when the daily minimum temperaturesare lower thantheir 10th percentile, are calculated for 10 Korean Meteorological Administration (KMA) stations over the period of 1960-2015. In all stations, the number of cold nights sharply decreased in the late 1980s. Astep-wise changeis largely due to the reduction in long-lasting events persisting for three consecutive nightsor longer. It is further found that the cold nights before and after the late 1980s areassociated with different synoptic and large-scale circulation patterns. While the pre-1980 events aremaintained by aneast-westdipolar sea level pressure (SLP) pattern with an anomalous high over Northern China and an anomalous low in the western North Pacific, the post-1990 events arecharacterized by a north-south dipole with an enhanced impact from Siberia and a reduced influence from the western North Pacific. In accordance with these synoptic patterns, the Pacific-related climate variability indices, such as the Pacific-North American (PNA) teleconnection index, exhibita negligible interannual relationship with the number of cold nights in the post-1990. These results suggest that the wintertime cold extremes over Korea in recent decades are influenced by different circulation patterns from those in the 1970s and 1980s.