A Numerical Study of an Intense Quasi-stationary Convection Band over the Korean Peninsula.

Abstract

An intense long-lived, quasi-stationary convection band that occurred on 5-6 August 1998 over the middle of the Korean peninsula, was studied using both observation and a numerical model. The convection band persisted for more than 10 hours, and produced heavy rain along the band with a maximum of 619 mm in 15 hours at a coastal station (Kanghwa). Radar observation indicates that the convection band is 20-30 km wide, and about 300 km long at its mature stage. It consists of several long-lived precipitation cells along the band. Some of the precipitation cells develop on the west coast, and move northeastward along the band. The convection band occurred over the middle of the Korean peninsula, where a converging airflow pattern is found between the mid latitude cyclone to the north, and the western Pacific subtropical high to the south. The simulated convection band forms and evolves in a consistent manner with the observation, although it shows notable differences from the observation in the onset time, lifetime and rainfall intensity. Formation of the simulated band proceeds in the following manner. First, new convection cells continuously form on the west coast and move northeastward forming a line of long-lived convection cells. Second, a line of low-level convergence forms somewhat rapidly in the upwind side of the convection initiation point, and then convective cells develop and move along this line. Some cells develop into deep convection and last several hours. These processes result in a long convection band. The favorable largescale condition (especially the converging airflow), and its interaction with convection, seem to be the important elements for the development of the present convection band. Surface latent heat flux is found to play a crucial role in establishing a convectively unstable environment for the onset of convection. It is also found that orographic effect is not an essential factor for the formation of the present convection band.