Development of a Diagnostic Index on the Approach of Typhoon Affecting Korean Peninsula

This study has developed the index for diagnosis on possibility that typhoons (TYs) affect Korea. This index is closely related to the strength of the western North Pacific high (WNPH), which is calculated as a difference in meridional wind between at the highest correlation area (around Korea) and at the lowest correlation area (sea southeast of Japan) through a correlation analysis between TC frequency that affects Korea and 500 hPa meridional wind. In low frequency years that selected from Korea affecting TC index, anomalous northeasterly is strengthened from Korea to the South China Sea because the center of anomalous anticyclonic circulation is located to northwest of Korea. Thus, TCs tend to move westward from the sea east of the Philippines to the mainland China. On the other hand, in high frequency years, anomalous southwesterly serves as steering flow that more TCs move toward Korea because the center of anomalous anticyclonic circulation is located to sea east of Japan. Consequently, this study suggests that if this index is calculated using real time 500 hPa meridional winds that forecasted by dynamic models during the movement of TCs, the possibility that TCs approach Korea can be diagnosed in real time.