Analysis of the diurnal cycle of convection during the genesis stage of tropical cyclones in preparation for TCS-08 in the Western Pacific region

The problem of tropical cyclogenesis is examined through various studies using data from the 2007 Western Pacific tropical cyclone season, with the goal of maximizing analysis and data collection opportunities during the Tropical Cyclone Structure 08 (TCS-08) field campaign. Convective bursts have been suggested to play an important role in tropical cyclone genesis by focusing convergence in the lowest levels of the pre-storm environment, thereby increasing low-level vorticity as predicted by the vorticity tendency equation. In order to identify favorable times for these convective bursts and thus optimal times to observe them, IR brightness temperatures from half-hour MTSAT-2 data are evaluated as a proxy for convective intensity. First, area averages of convective intensity are constructed for the prime genesis regions in the West Pacific in order to fully document the diurnal cycle of convection. These results indicate the presence of a diurnal maximum near sunrise during the late August-September time period (corresponding to TCS-08 field campaign dates). Next, eight typhoons from the 2007 season are interrogated. During the genesis stage, the cycle of active convection occurs in the late evening to early morning hours with 2-3 convective peaks (or bursts). Although the early morning peak is always present, it is not always the most intense convective burst. Finally, properties of these convective bursts and an attempt to identify favorable times and conditions for observing them are discussed. These results will prove critical to selecting appropriate flight patterns and times to comprehensively observe tropical cyclogenesis, a key objective of TCS-08.