The spatio-temporal characteristics of total rainfall during September in South Korea according to the variation of ENSO

摘要

A significant negative correlation between the total rainfall averaged over South Korea and the Nino-3.4 index was found for the month of September. To find out the reason for this negative correlation, composite analyses were carried out for the highest and lowest 8 years of the Nino-3.4 index. During the strong El Nino year, an anomalous anticyclone occurs in the continental East Asia, while an anomalous cyclone emerges in the subtropical western Pacific. The resultant eastward pressure gradient force induces anomalous northerlies in most regions of East Asia, which produces anomalous cold and dry conditions throughout the troposphere between 120° and 140°E, reducing the Korean rainfall. It is also found that during El Nino year, tropical cyclones (TCs) tend to recurve far east offshore of Japan because the weakening of the western North Pacific subtropical high (WNPSH). During La Nina years, on the other hand, the strengthening and westward extension of the WNPSH render more TCs influencing the Korean peninsula. Therefore, the TC track changes associated with El Nino-Southern Oscillation is another contributor to change of the Korean rainfall.