Thursday, 9 August 2007
Halls C & D (Cairns Convention Center)
Summer monsoon period called Changma in Korea (like Baiu in Japan and Meiyu in China) normally starts in late June and ends in late July, which has mesoscale systems with multi-scale features along front. As it has been known, there are many studies on the synoptic conditions of disturbances produced heavy rainfalls over Meiyu-Baiu frontal zone. However, there are few studies on disturbances in mesoscale aspects, based on the radar observation data in the Korean Peninsula. Therefore, the purpose of the present study is to investigate the kinematical variation of a mesoscale disturbance by Dual Doppler radar observation data. The data was obtained during the periods of KEOP (Korea Enhanced Observing Project), 21 June to 5 July 2006, which was focused on analysis of the change of the disturbance configuration, variation of wind field and rainfall intensity distribution including topographic effect on the disturbance. The analyzed system was originated near Jiangsu, northern downstream region of Yangtze River of China, at 2300 LST 30 June 2006 and propagated to the middle of Japan through the southern part of the Korean Peninsula with the speed of 65 km/h. It was oriented in the north-south direction, and consisted of three major regions: one convective rainfall region and two weak stratiform rainfall regions. One weak stratiform rainfall region was ahead of the one convective rainfall region while the other was developed behind the convective region. During its approach to the Korean Peninsula, the arc-shaped convective system was converted to the line-shaped convective system by the topographic effect and the change of environment around the system. The line-shaped convective system had a weak wind along the upper frontal line and a disturbance occurred below the altitude of 3.5 km in the rear of system from 0730 to 0820 LST 1 July. In mature stage, the disturbance greatly enhanced the convection of the system, in which the strong vertical air velocity was over 8 ms-1, the horizontal convergence, 24×10-4 s-1 and the horizontal vorticity, 22×10-4 s-1. There was a strong vertical wind shear in the system. The system began to dissipate after the line-shaped convective system passed the ocean between the Southern boundary of Korean Peninsula and Jeju Island with Mt. Halla. This is because the topographic effect of Mt. Halla significantly modified both the shape of the convective system and the speed of air flow. During the passing of the system over the ocean, the air flow speed was greatly increased, and then induced a strong divergence, causing the decay of the system.
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