Knowledge Discovery of Influencing the Movement of Mesoscale Convective System
GUO Zhong-Yang, LIN Hui, DAI Xiao-Yan, JIANG Ji-Xi, WU Jian-Ping (Department of Geography & Joint Laboratory for GeoInformation Science, the Chinese University of Hong Kong, Hong Kong, China; Laboractory of Geography Information Science, East China Normal University, Ministry of Education, Shanghai 200062; National Satellite Meteorological Center, China Meteorological Administration, Beijing 100081)
Recently, the evidences have indicated that the heavy- rainfall in Yangtze River Basin is directly caused by Mesoscale Convective System (MCS) over the Qinghai-Xizang Plateau in China. In this project, the trajectories of MCS over the Qinghai-Xizang Plateau are automatically tracked using CMS ( Geostationary Meteorological Satellite) infrared black-body temperature (Tbb) and High Resolution Limited Area Analysis and Forecasting System (HLAFS) values provided by China National Satellite Meteorological Center from June to August 1998. Among these data, spatial resolution of Tbb is 0.5° lat (0.5°long, time resolution of Tbb is one hour). And, spatial resolution of HLAFS is 1 ° lat ( 1 ° long and time resolution of HLAFS is twelve hours) . On the other hand, research range of latitude is from 27° to 40°N, and longitude is from 80° to 105°E. While levels include 400hPa and 500hPa. Furthermore, the study focuses on MCS that cover at least 3 connected pixels having Tbb≤-32℃ in each Tbb image, and last for at least 3 consecutive hours. Before spatial association rule mining, MCS is firstly tracked, in this project, if an MCS moves across 105?E, then the MCS is defined as " move-out of the Plateau" , otherwise, it is defined as " stay in" . Results indicate that there are 749 MCSs over the Qinghai-Xizang Plateau from June to August 1998. While the total number of MCS, which move out of the plateau, is 55. And, results also show that the initiation locations of most of MCSs, which moving out of the Qinghai-Xizang, are between 100°E and 105°E. Therefore, the initiation location of each MCS is defined near 100°E. On the other hand, in the course of spatial association rule mining, the parameters, isobaric surface height, temperature, relative humidity, vorticity, divergence, vertical velocity, water vapor flux divergence, θSE, K index , area, the lowest Tbb, position and shape of MCS are included. Based on these, the relationships between the trajectories of MCSs of moving out of the Qinghai-Xizang and their environmental physical field values are analysed using spatial association rule mining technique, the results indicate that at a level of 400 hPa, the MCSs, which move out of the plateau and to east, are not related with temperature, the lowest Tbb, area and location of MCS. Furthermore, the association rules, with the confidence of 1.0, are only related with isobaric surface height, relative humidity, vorticity, divergence, vertical velocity and K index. By and large, at this level, the MCS of moving out of the plateau to east is mostly determined by i-sobaric surface height, relative humidity, vorticity, divergence and vertical velocity. While at a level of 500 hPa, the MCSs, which moving out of the plateau, are not related with θSE, water vapor flux divergence, location and area of MCS. Furthermore, the trajectories of MCSs are less influenced by vorticity, divergence, the lowest Tbb and shape of MCS. By and large, at this level, the trajectories of MCSs are mainly influenced by isobaric surface, relative humidity, temperature, vertical velocity and K index.