Mesoscale Convective Systems at Tropical Cyclone Formation Time from Microwave Satellite Observations

Recently, it has been well emphasized that distribution and structure of mesoscale convective systems (MCSs) in a synoptic-scale tropical disturbance are of significance in tropical cyclone formation. Although aircraft radar observations during special field experiments (TCS-08 or PREDICT) enabled more detailed kinematic and dynamic structures of convection, observations of convections just prior to tropical cyclone formation are absolutely rare. In this study, multi-year TRMM microwave Imager (TMI) 85 GHz polarized corrected temperatures (PCT) are used to detect ice scattering signatures from convective towers and stratiform precipitation regions of MCSs in developing and non-developing tropical disturbances. The microwave ice scattering methodology has been used for investigating features of MCSs over tropical and subtropical regions, and the focus of this study is at tropical cyclone formation stage. In particular, this study analyses number of MCSs evolving within tropical disturbances, and size of each MCS, minimum and average PCT values for each MCS, and etc. The microwave PCT analyses indicate that multiple but smaller-scale MCSs are prevalent in pre-formation stage disturbances. At tropical cyclone formation time, the size of the largest MCS within a disturbance is enlarged and minimum PCT value tends to be lowered. It is also notable that there are many non-developing MCSs that have larger-scale organization and extreme ice scattering, but surface cyclonic circulation was absent from Windsat observation. The microwave PCT analyses also indicate that the size of the MCS is relevant to whether the developing disturbance can later intensify into tropical storm/typhoon. ->244645 modified by 121.144.78.57 on 11-22-2013-->