An Investigation of Mechanism of Typhoon Durian (2001) Genesis Associated with Monsoon Trough.

The genesis of Typhoon Durian (2001) from a monsoon trough over the South China Sea is investigated using the NCEP analysis, the TMI sea surface temperature (SS T) data and satellite imageries. The results reveal the important roles of large rscale flows, warm SSTs, and convectively generated vortices in determining th e TC genesis. Of importance is the timing of the TC genesis. Durian appeared as the vertical wind shear decreased to a critical value of 10 m／s as a result of changing largerscale flow pattern in the upper troposphere. It is shown that t he monsoon trough was conditionally unstable to deep convection and barotropical ly unstable to mesoscale disturbances. Low-level jets associated with a cross -equatorial flow and a westerly flow from IndoChina Peninsula provided favo rable lifting-?e air in the boundary layer for the development of two major convective bands to the south of the trough axis. As the two convective bands, spaced meridionally about 300 km apart, moved toward the trough axis, the associated vortices were merged into the monsoon trough, leading to the generation of an MCV and its subsequent growth to typhoon intensity. It is also shown that surface heat fluxes from the underlying warm ocean played an important role in feeding convective available potential energy to deep convection during the TC genesis. We conclude that the genesis of Typhoon Durian involved multi-scale processes, including vortical hot towers, upscale growth to vorticity bands, their merging to an MCV, and the large-scale control of the timing and location within the monsoon trough.