| Summary: | Despite progressing global warming, extreme cold events in East Asia are still occurring frequently with temperature variability enhanced. To understand this situation, it is necessary to determine external and internal climatic factors and their modulation effects that influence regional temperature variability. We found that the positive correlation between Arctic Oscillation (AO) and surface air temperature (SAT) in South Korea during winter is modulated strongly by tropical influences associated with El Niño Southern Oscillation (ENSO). In the case of a negative (positive) SAT anomaly in South Korea during the positive (negative) AO phase, a state that is opposite to the typical relationship between AO and SAT, the tropical sea surface temperature shows a typical negative (positive) ENSO-like pattern. The atmospheric teleconnection associated with the negative (positive) ENSO conditions contributes to a deepening (flattening) of the climatological East Asian trough and an enhancing (weakening) of the East Asian jet, which leads to negative (positive) SAT anomalies in South Korea. This modulation effect is robustly observed in the historical simulations of three different models of CMIP5.
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