Influence of Sea Surface Temperature on a Mesoscale Convective System Producing Extreme Rainfall over the Yellow Sea

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 degrees C higher than the 30-yr climatological mean, and a local warm pool (>28.5 degrees 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.