A Study on Tropical Cyclone (TC) Structure Changes and Organized Convections associated with TC-Environment Interactions

In the western North Pacific, organized mesoscale convective system (MCS) sometimes occur while tropical cyclones (TC) interact with the strong environmental flows. In this study, the impacts of the organized convections on TC structure changes and the favorable environmental conditions for the formation of such organized convections are examined. During 1999-2009, a total of 160 organized MCS's are identified using infrared images and passive micro-wave images. An organized MCS has to have a considerably large cold cloud anvil which sustained for more than 6 hours. Furthermore, these organized MCS's have to be associated with the interactions between TCs and the environmental southwesterly flows. Results showed that 36% of all typhoons in the western North Pacific have at least one organized MCSs during its life period. According to their locations with respect to the TC center, these systems can be classified into two types: inner MCS (76 cases) and outer MCS (84 cases). Results also show that although both the inner-type MCSs and the outer-type MCSs have similar environmental flow pattern, their impacts on TC structure changes are quite different. When an inner MCS occurs, the TC usually increases its size with a faster rate and the intensification rate remains the same. However, the increasing rate of size remains the same but the intensification rate becomes slower when an outer MCS occurs.