호남지방에 발생한 호우성 대류밴드에 관한 연구

Abstract

ABSTRACT

A Study of Convective Band with Heavy Rainfall occurred in Honam region

Moon Tae Su Advisor : Prof. Ryu, Chan-Su, Ph.D. Department of Atmospheric Science Graduate School of Chosun University

Damage due to Torrential rains occurred every year Constantly is recurring up Constantly. Especially, it is very difficult to predict where and when the heavy rainfall occurs due to its unique characteristics with very short time of duration and very small scale of system. For these reasons, nowcasting is preferred when forecasting severe weather related to meso-scale convective system. However, it is required that a forecaster analyzes meso-scale convective system throughly in order to overcome the limitation of nowcasting. Hence, this study investigates the synoptic / meso-scale analyses and lifescale characteristics of 10 cases which occurred at Honam region for JJA, 2009-2012(Heavy rain monitoring period). From synoptic perspective, it is concluded that convective band with heavy rainfalls happens under the periphery of N. PAC high condition or under the impact of it due to higher convective temperature than daily maximum one, and large equivalent potential temperature. On the meso-scale analysis, the horizontal and vertical radar data at Mt. Osung, which covers the entire Honam region, is mainly used to analyze the initiating, developing, mature, and dissipating stage of convective band. The convective band with heavy rainfalls initiates due to convergence of sea breeze around three hours before or after the time that the daily maximum temperature happens. As the warm pool is formed around Honam plains, the converging types of sea breeze from the West and South Seas are one-point oriented or straight-lined. And the location of convergence, depending on pressure gradient force, is around the south coast or Cheonbuk Province. At the occurrence stage, The precipitation intensity is weak due to multiple cells, and there are small scale of convective cells. When airflow of surface converged, even in places where no convection cells, high-EPT Dense zone appeared around the surface. In the mid level of 850hpa~500hpa, there is low-EPT and showed conditions unstable state. It wasn't appeared convergence zone in low level and mid-level. Development of a convection band went equipped with some form. The main factor developing the form of the primary cause tends to rely a lot form of airflow convergence. Broken linear type also made Completed linear type through Cell merging. Also, It began to show authentic band moving, almost stagnated or moved quickly in one direction or change the direction of movement etc. When the convective cells merge, Horizontal and vertical intensity increased, too. Thus, Increase the area and intensity of precipitation. Vertically, high EPT zone is extended until mid-level. High Humidity zone of low level moved to 500hpa, mid-level. Convergence zone from surface to mid-level was stronger and updraft wind increased. At the mature stage, the heavy rainfalls begins with strong downburst that causes such a sudden temperature drops that the pressure and temperature gradients reach the maximum. And the strong downburst induces the new convergence area, called a gust front that made a kind of new convective cells. As the area with heavy rainfalls is moving along the convective band, the gust front is following along the system, and it’s causing increase in wind speed and wind shift. high EPT zone vertically rose over mid-level at the mature stage , connected High EPT zone of high-level and low EPT of mid level was separated left and right. High humidity zone moved to high level along high EPT. Updraft and Convergence increased along high EPT. At the dissipating stage, the precipitation weakens with dissipating downdraft, and decreasing thermal/pressure gradient forces. Also, the sea breeze moving into the land stops due to temperature change, the convective band is separated or dissipated. Vertically, the portion of convective band dissipated and is separated due to penetration of low EPT along with northwesterly wind on high EPT area.