Influence of Kamchatka Blocking and East Asian winter monsoon on the winter 2m-temperature over South Korea

This study examines the factors affecting the 2m-temperatures (T2m) in South Korea in winter (DJF) from 1979/1980 to 2018/2019. For this purpose, we performed an empirical orthogonal function (EOF) analysis of the geopotential height at 500 hPa in the region 15 & DEG;-75 & DEG;N, 70 & DEG;E-180 & DEG; centred around the Korean Peninsula. The first EOF mode, which accounted for 31.1% of the total variance of the winter T2m in the region, is related to the KamChatka Blocking Frequency (KCBF). The second mode, which accounted for 18.3%, is associated with East Asian winter monsoon (EAWM). In addition to EOF analysis, the partial correlation (PC) analysis also confirmed that KCBF Index and EAWM Index, which are highly correlated with the winter T2ms in South Korea, are independent of each other. The individual and combined effects of the KCBF and EAWM are examined because they independently affect the winter T2ms in South Korea. According to the composite analysis, in the years when KCBF is higher than normal (H_KCBF), negative and positive Z500 anomalies are located over the south Sea of Japan and the Kamchatka Peninsula, respectively. In other words, the positive geopotential anomaly over the Kamchatka Peninsula lowers the T2ms of South Korea by blocking the flow of cold air moving eastward from the Korean Peninsula. In the years when a strong EAWM occurred (S_EAWM), negative and positive Z500 anomalies are located over the Manchuria region and the northwestern regions of Russia, respectively. Consequently, cold air in the north moves southward, resulting in lower T2ms in South Korea. For the combined effects of KCBF and EAWM on the T2ms, winters of 40 years are categorized into L_KCBF-W_EAWM, L_KCBF-S_EAWM, H_KCBF-W_EAWM and H_KCBF-S_EAWM years. The analyses show that when KCBF and EAWM are in phase, the T2ms in South Korea are more prominent than when they are out-of-phase.