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Title: Rainfall distributions over land associated with tropical cyclones making landfall along the south China coast
Other Titles: Re dai qi xuan zai Hua nan hai an deng lu qi jian de lu di jiang shui fen bu
Authors: Fung, Kit Ying (馮潔瑩)
Department: School of Energy and Environment
Degree: Master of Philosophy
Issue Date: 2010
Publisher: City University of Hong Kong
Subjects: Rain and rainfall -- China.
Cyclones -- Tropics -- China.
Notes: CityU Call Number: QC925.5.C62 H665 2010
xiii, 87 leaves : ill. (some col.) 30 cm.
Thesis (M.Phil.)--City University of Hong Kong, 2010.
Includes bibliographical references (leaves 83-87)
Type: thesis
Abstract: Rainfall distributions over land when tropical cyclones (TCs) made landfall along the South China (SC) coast during 1992 - 2007 are studied and changes in rainfall distributions as TCs are at 50 km offshore before, during and 50 km onshore after landfall are also examined, all based on raingauge data. For studying the rainfall distribution over land during landfall, TCs are divided into inner (In) zone with radial distances from TCs centers are less than 100 km and outer (Out) zone with radial distances from TC centers are between100 - 300 km. In examining the variation of rainfall distribution over land when TCs are at different perpendicular distances from the coastline, TCs are divided into left and right quadrant with radius of 300 km. For all situations, the enhancement of rainfall over land is in general found in the right quadrant of TCs. Vertical wind shear is one of the contributors towards the asymmetric rainfall distributions over land. The relationship between the individual vertical wind shear and the rainfall distribution is not well related. However, a composite of the vertical wind shears shows that it can explain the enhancement of rainfall in RF. Most of the TCs are found to experience northeasterly and southeasterly vertical wind shear during landfall and it is related to the environmental flow. In addition, the vertical wind shear shows no significant change in direction when TCs are at 6 hours before, during and 6 hours after landfall but a sharp change is found between the time of 12 hours to 6 hours before landfall. This variation of vertical wind shear with time may be related to the interaction between land and the TC. Land interacts with TC through topography. Convergence of vertically integrated horizontal water vapor flux is also a factor that can enhance the rainfall in RF because the convergence of water vapor dominates in RF, resulting in enhanced condensation and finally the stronger precipitation over there. Since topography is hypothesized to be the contributor to the asymmetric rainfall distributions over land, the Weather Research and Forecasting model is used to simulate its effect. Four groups of TCs are simulated. In each group, two TCs are simulated one with and another without topography. A larger extent of rainfall enhancement is found in RF for TCs with topography. Moreover, the variation of vertical wind shear in the simulations with topography is consistent with that in the observational studies. Finally, there is a positive relationship between terrain height and the extent of rainfall enhancement in RF.
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