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Jong-Hoon Jeong
,
Dong-In Lee
, and
Chung-Chieh Wang

Abstract

In this study, an extreme rainfall-producing quasi-stationary mesoscale convective system (MCS) associated with the Changma front in southeastern South Korea is investigated using numerical simulations and sensitivity tests. A record-breaking rainfall amount was recorded in response to repeated initiation of new cells (i.e., back-building) over the same area for several hours. The aim of this study is to realistically simulate and analyze this extreme rainfall event to better understand an impact of the cold pool that leads to the quasi-stationary MCS over southeastern South Korea by using a convection-allowing-resolution (2 km) nonhydrostatic atmospheric model.

The control experiment (CNTL) was successfully performed, yielding the quasi-stationary, back-building MCS at approximately the correct location and time. In the CNTL run, diabatic cooling due to evaporation of raindrops was responsible for the formation of the cold pool. The development of the cold pool was responsible for the deceleration of the propagating convective line, which played a role in the stalling of the MCS over southeastern South Korea. Moreover, new convective cells were repeatedly initiated in the region where an oncoming warm inflow met the leading edge of the cold pool and was uplifted. In an experiment without evaporative cooling (NOEVA), the simulated precipitation pattern was shifted to the northeast because the MCS became nonstationary without the cold pool. The cold pool had an essential role in the stationarity of the MCS, which resulted in extreme rainfall over the Busan metropolitan area.

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Yunhee Kang
,
Jong-Hoon Jeong
, and
Dong-In Lee

Abstract

An extreme-rainfall-producing linear mesoscale convective system (MCS) occurred over the Yellow Sea, Korea, on 13 August 2012, producing 430 mm of rainfall in less than 12 h, causing devastating flash floods and landslides. To understand the causative processes underlying this event, we examined the linear MCS’s formation and development mechanisms using observations and cloud-resolving models. The organized linear MCS produced extreme rainfall at Gunsan in a favorable large-scale environment. The synoptic environment showed the stationary surface front elongating from China to Korea; a southwesterly low-level jet transported the warm, moist air from low latitudes toward the front. In the upper-level synoptic environment, the trough and entrance regions of the upper-level jet were north of the heavy rainfall, promoting the development of convection. The extreme rainfall over the Gunsan area resulted from the back-building mode of the MCS, in which new convective cells continued to pass over the same area while the entire convective system was nearly stationary. The sea surface temperature (SST) during the extreme rainfall events was abnormally 1°C higher than the 30-yr climatological mean, and a local warm pool (>28.5°C) existed where the convective cells were continuously initiated. Cloud-resolving models simulated the low-level convergence, and the latent heat flux was large in the local warm SST field. These induced MCS formation and development, contributing to a significant rainfall increase over the Yellow Sea. The terrain’s influence on the large rainfall amount in the area was also noted.

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