The Doppler radar and High-Resolution Model analysis of extreme rainfall producing quasi-linear convective system on 7 July 2009, Busan, Korea

The Korean Peninsula experiences extreme rainfall events every year in associated with typhoons, synoptic disturbances, mesoscale convective systems, and summer monsoon circulation from June to September. Extreme rainfalls have been observed over the Korean Peninsula and have caused heavy loss of lives and property. In this case for extreme rainfall occurred on 7 July 2009, an intense and quasi-linear convective systems persisted for more than 5 hours and produced a large rainfall amount around 362 mm for 12 h at Busan metropolitan area. The hourly rainfall was recorded to 73 mm, which was the strongest severe weather event ever observed in Busan metropolitan area.

To investigate the extreme rainfall events over southern Korean Peninsula, we used S-band Doppler radar data and performed numerical simulation. Cloud-Resolving Storm Simulator (CReSS) Model is used to conduct nested high-resolution (2 km) simulations, which is a three-dimensional non-hydrostatic numerical model.

In the radar analysis, the convective systems appeared quasi-linearly as a back-building type. The convective cells continually formed and repeated over the same location within an area of stratiform cloud. It could result in flash flood over Busan area. In simulation results, surface low pressure appeared over the western Korean Peninsula, they showed cyclonic circulation around low pressure. The development of low pressure resulted in horizontal and vertical wind shear due to cyclonic circulation. The mid-level cyclonic vorticity took place to heavy rainfall region. In addition, the moisture was significantly advected by southwesterly low level jet. Even convective parameters (CAPE, CIN) showed little instability, the enhanced vorticity and moisture advection could result in destabilization around convective region.