Summer and autumn tropical cyclone activity over South Korea responds in opposite ways to ENSO phases

Abstract It is known that the El Niño Southern Oscillation (ENSO) is not a factor in the interannual variation of the number of tropical cyclones (TCs) affecting South Korea during the TC season, which generally includes both summer (July-August) and autumn (September-October). By dividing the TC season into two sub-seasons, i.e. summer and autumn, we found the opposite response of TC activity over South Korea to ENSO phases between the sub-seasons. In summer, a larger number of TCs influence South Korea during El Niño than during La Niña, while a smaller number of TCs do so in autumn. The opposite responses to ENSO could reduce the statistical significance of the relationship between ENSO and TC activity over South Korea when the entire TC season (July to October) is considered. In summer, the southerly anomaly over the southern sea of the Korean peninsula due to the eastward retreating subtropical high allows a greater number of TCs to approach South Korea during El Niño compared to La Niña. On the other hand, in autumn, the northwesterly anomaly due to the westward extension of the subtropical high leads to a smaller number of TC approaches.