Analysis of rainfall generation process in east Asia by Summer Cold Wave

In August 2022, extremely heavy rainfall occurred in the central region of the Korean Peninsula. On August 8, Seoul received 381.5 mm of rain, the most in 115 years. Heavy rain is a phenomenon that accounts for the most significant portion of dangerous weather occurring in Korea, and many studies, including the mechanism of occurrence, have been done on this phenomenon. However, the synoptic pressure pattern that caused heavy rain in August 2022 differed from the rainfall pattern studied in general. The pressure system around the Korean Peninsula also showed a different pattern from the typical summer pressure characteristics. As a result, by reviewing the pressure system specificity of the Korean Peninsula and the Eurasian continent, this study investigated the mechanism and climatological factors of heavy rain in August 2022. In August 2022, strong high pressure developed over the Eurasian continent, the Kamchatka Peninsula, and the Ural Mountains. On August 8, a stationary front crossing the Korean Peninsula from east to west was located. To determine the specificity of the barometric pressure system, the air temperature and barometer of the ground and upper layers were analyzed using ECMWF's ERA-5 reanalysis data. At the surface level, high pressure intensified near the Ural Mountains and Lake Baikal in Siberia in early August. In the case of temperature, the advection of cold air below a -5°C anomaly from high latitudes to the northwest of the Korean Peninsula through Siberia following the flow of lower high pressure is analyzed. At 500 hPa, upper-level blocking was observed in the Ural Mountains and the Kamchatka Peninsula. The blocking over the Eurasian continent reduced zonal flow while increasing meridional flow. Cold air from the high latitudes was transported to East Asia by the increased meridional flow. The cold air that moved toward East Asia met the edge of the North Pacific high pressure and formed a stationary front, causing heavy rain. In this study, the development of a cold continental high pressure in summer affecting the mid-latitude region was defined as the "Summer Cold Wave" (SCW), and the development of the front by the SCW was defined as the "Summer Cold Front" (SCF). In addition, by analyzing cases where SCW occurred in the past, it was determined that the development of Ural blocking in summer influenced the occurrence of SCW, and it was determined that precipitation due to SCF increased in the Korean Peninsula when the North Pacific high pressure occurred strongly.