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.

Three distinct atmospheric circulation patterns associated with high temperature extremes in South Korea

“…2 b). This structure highly correlates with a northward-propagating wave train, such as the widely known PJ teleconnection pattern 5 , 14 , 18 , 22 , 24 and meridional wavelike pattern 20 . Contrarily, there is no statistically significant circulation anomaly over the Eurasian continent (Fig.…”

“…A record-breaking number of EHDs and droughts occurred in East Asia, causing more than 3,000 deaths in South Korea in 1994 11 . However, it is important to recognize that recent severe EHDs cannot be explained solely by the thermodynamic effects of global warming 12 – 14 .…”

“…Many previous studies have emphasized the importance of the dynamic effects that induce EHDs 5 , 12 , 14 , 18 – 22 . Dynamically, a persistently positive geopotential height (GPH) anomaly is accepted as the most important atmospheric factor leading to the occurrence of EHDs because it provides favorable conditions for EHDs via adiabatic warming caused by downward motion 20 , 22 , 23 .…”

“…Dynamically, a persistently positive geopotential height (GPH) anomaly is accepted as the most important atmospheric factor leading to the occurrence of EHDs because it provides favorable conditions for EHDs via adiabatic warming caused by downward motion 20 , 22 , 23 . Focusing on the Korean Peninsula, EHD-related atmospheric circulation patterns are intimately associated with two types of wave trains generated by enhanced convection over the subtropical western North Pacific (WNP) 5 , 14 , 18 , 20 , 22 and mid-latitude Northern Hemisphere wave dynamics 14 , 19 , 20 – 22 . For instance, enhanced convection over the South China Sea acts as a source of the northward-propagating wave train, which resembles the Pacific-Japan (PJ) teleconnection pattern 24 .…”

“…This long-term change in the GPH anomaly was due to the phase transition of the summer NAO from positive to negative. However, the 500-hPa GPH anomalies over East Asia and the North Pacific (i.e., 0°–70° N, 80°–230° E) were used as input for clustering analysis, even though the EHDs in South Korea are influenced by the eastward-propagating wave train across the Eurasian continent 14 , 19 , 20 – 22 . Furthermore, the northward-propagating wave train, forced by enhanced convection over the WNP 5 , 14 , 18 , 20 , 22 , 24 , which is a major mechanism associated with the EHDs in South Korea, is not captured in their clustering results (Fig.…”