An investigation has been made to understand the development mechanisms for the heavy rainfalls of 6-7 August 2002 over the middle of the Korean peninsula, using both observations and a numerical model. This paper describes 1) the observed heavy precipitation systems, 2) the environment and its relation to the heavy rainfalls, 3) simulated heavy rainfalls and the role of latent heat release, and 4) themechanisms for the heavy rainfall development.
Heavy rainfalls occurred over the mid-peninsula with a maximum precipitation amount exceeding 300 mm during the 18-h period of 12 UTC 6-06 UTC 7 August. Observations showed that convection bands continuously developed over the Yellow Sea and coastal area near the mid-peninsula. They moved eastward, and embedded convective cells developed into deep convections, producing heavy rainfalls over the coastal and inland areas. A large meso-β-scale rainfall area with several heavy-rain cells formed in land, ahead of the low-level jet (LLJ) maximum area where strong convergence occurred. A close relationship was found among the LLJ, upper-level jet streak (ULJS), and heavy rainfalls. In this event, large-scale conditions not only provided a favorable environment for the development of the heavy rainfalls, but also actively interacted with mesoscale systems.
Simulation using MM5 has well reproduced the convection bands over the coastal area, and the large meso-β-scale rainfall area with heavy-rain cells over the inland area. Simulated results suggest two types of band formation: one initiated by an elongated convergence of large-scale flows, and another initiated by convective cells existing in a strong southwesterly air stream. Simulations also indicate that both the LLJ and ULJS are intensified and maintained by convective heating. A favorable, large-scale environment, and its interaction with convective systems, may be the primary reason for the persistence of the heavy rainfalls.