Formation and evolution of mesoscale convective systems that brought the heavy rainfall over Seoul on September 21, 2010

An investigation has been carried out using observational data and a numerical model to explain the formation and development of heavy precipitation systems on September 21, 2010. These systems were responsible for heavy rainfall over the middle Korean peninsula, with a maximum 24-h rainfall amount greater than 290 mm in the Seoul metropolitan area. Both observational analysis and a numerical simulation indicate that an important starting condition for this heavy rainfall event is the presence of a pressure trough over the Shandong peninsula and the Yellow Sea. Convective cells formed in the early morning over this trough area, grew into larger systems as they moved eastward, and induced the formation of a meso low over the Yellow Sea around 0000 UTC on September 21, 2010. A stationary front with significant vertical circulation developed in response to the deformation of flow associated with the meso low. In the meantime, multicell-type convective systems continuously developed and moved along the front. These storms developed further and produced heavy rainfall over the middle Korean peninsula, which includes the Seoul metropolitan area. According to observations, the band structure appeared to change after 0700 UTC as a narrow convection band developed over the sea, upstream of the existing band of multicell storms. Numerical simulation showed a similar transition. However, it failed to reproduce the stationary behavior of the observed band.