Physical and dynamic factors that drove the heavy rainfall event over the middle Korean Peninsula on 26-27 July 2011

Abstract

This study used an observational analysis and a numerical model to investigate the heavy rainfall event that occurred on 26-27 July 2011 over the middle Korean Peninsula. Radar observations revealed a significant transition in the echo pattern, with strong convective systems along the coasts of southern Hwanghae-do (HHD) and Gyeonggi-do (0600-1200 UTC 26 July, stage 1), a medium-sized SW-NE precipitation band over the middle Korean Peninsula and major convective systems in the west (1500-2200 UTC, stage 2), and a narrow convective band from Gyeonggi Bay to the Seoul metropolitan area (2200 UTC 26-0100 UTC 27 July, stage 3). This study focused on the development of heavy precipitation systems during stages 1 and 2. A mesoscale ridge and trough developed over the middle peninsula at approximately 0600 UTC on 26 July and persisted throughout the first 2 stages. Both the observation and the numerical simulation suggest that a cold pool, which induced the mesoscale ridge, developed over the inland HHD in response to evaporative cooling of rain water. The outflow associated with the cold pool was found to trigger the strong convective systems along the southern coast of HHD in stage 1. The lifting of air in the precipitation band of stage 2 was mainly caused by convergence ahead of the strong low-level southwesterly flow. The numerical simulations indicated that the terrain over the Korean Peninsula contributed to the enhancement of the heavy rainfall primarily through its blocking effects on oncoming southwesterly airflow at low levels.