Physical–Statistical Model for Summer Extreme Temperature Events over South Korea

Abstract

Extreme temperature events have a significant impact on human life and property. Since the Korean Peninsula is affected by the high variability of the East Asian summer monsoon system, it is difficult to predict extreme temperature events skillfully. Here, we construct an empirical model to investigate the interannual variation of the frequency of summer extreme temperature events over South Korea by identifying predictors (explanatory variables) from ocean boundary conditions. The selected explanatory variables are sea surface temperature anomalies (SSTAs) over the North Atlantic, the western North Pacific, and the eastern North Pacific. The cross-validated correlation skill of the statistical model constructed using a 23-yr dataset is estimated to be 0.77. A common feature that all three explanatory variables contain is the development of an anticyclonic circulation anomaly over the Korean Peninsula. The North Atlantic SSTA predictor acts as a forcing mechanism for the generation of Rossby wave trains downstream, developing an anticyclonic circulation anomaly in the lower and upper troposphere over the Korean Peninsula. The western North Pacific (WNP) warm SSTA predictor induces a cyclonic circulation anomaly over the WNP and an anticyclonic circulation anomaly over the Korean Peninsula, resembling the Pacific?Japan teleconnection mechanism that represents the northward Rossby wave propagation over the western Pacific. Through air?sea interaction, the tripolar SSTA pattern in the eastern North Pacific representing the North Pacific gyre oscillation induces two opposite precipitation anomalies in the equatorial Maritime Continent and the Philippine Sea. These diabatic anomalies excite northward-propagating Rossby waves that form a cyclonic circulation anomaly in the WNP area and an anticyclonic anomaly over the Korean Peninsula.