THESIS
2008
xxiv, 220 leaves : ill. (some col.) ; 30 cm
Abstract
This research investigates several issues pertaining to tropical cyclogenesis over the South China Sea (SCS), one region under the significant influence of the East Asia Monsoon. Analyses of satellite observations and reanalysis datasets plus numerical simulations are applied to investigate the mechanism of tropical cyclogenesis over the SCS....[
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This research investigates several issues pertaining to tropical cyclogenesis over the South China Sea (SCS), one region under the significant influence of the East Asia Monsoon. Analyses of satellite observations and reanalysis datasets plus numerical simulations are applied to investigate the mechanism of tropical cyclogenesis over the SCS.
The climatology of environmental conditions associated with the monsoon and their influences on tropical cyclogenesis in the SCS are examined. Comparisons are made for environmental conditions between the major formation area and the no formation area, and between a tropical cyclone active year and an inactive year over the SCS. The importances of different climatological environmental factors to tropical cyclogenesis over the SCS are clarified.
Environmental conditions prior to tropical cyclogenesis due to synoptic-scale disturbances are investigated. Comparisons are made for environmental conditions between non-developing tropical disturbances and developing tropical disturbances. It is shown that the amount of total latent heat release can distinguish between non-developing and developing tropical disturbances. Environmental parameters which are statistically relevant to latent heat release are determined and the importance of each parameter is assessed quantitatively. The statistics reveal threshold values useful to forecasters in the tropical cyclone formation forecast.
The genesis of one tropical cyclone over the SCS ---- Typhoon Durian (2001) was simulated using the WRF model. The formation of typhoon Durian in a monsoon trough environment was reproduced by numerical simulations. Two numerical experiments in which the sea surface temperature (SST) was either decreased or increased were performed to investigate the mechanism of cyclogenesis and the impact of the SST on the genesis of the typhoon.
Based on the results in this study, one mechanism is proposed to explain tropical cyclone genesis ---- Coupling of Lower-Upper Troposphere (CLUT): Persistent large amount of latent heat release is the critical condition for tropical cyclogenesis, which determines one tropical disturbance to develop or not; The large amount of latent heat release is induced by the lower-upper tropospheric coupling; The reasons why non-developing disturbances can not develop into tropical cyclones are due to the deficiency of lower-upper tropospheric coupling in dynamic conditions and/or in thermal conditions.
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