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Title: The Role of diabatic heating in tropical cyclone motion
Other Titles: Fei jue re guo cheng zai re dai qi xuan yun dong zhong de jue se
Authors: Lei, Ying-man (李應文)
Department: Dept. of Physics and Materials Science
Degree: Master of Philosophy
Issue Date: 2000
Publisher: Dept. of Physics and Materials Science, City University of Hong Kong
Subjects: Cyclone tracks
Cyclones -- Tropics
Notes: CityU Call Number: QC948.L44 2000
Includes bibliographical references (leaves 79-87)
Thesis (M.Phil.)--City University of Hong Kong, 2000
xiii, 97 leaves : ill. ; 30 cm.
Type: Thesis
Abstract: Researchers have attempted to use baroclinic processes to explain tropical cyclone (TC) motion. In those explanations, vertical vortex coupling mechanisms should be involved. However, the details of such mechanisms are still ambiguous and controversial. A recent concept is to use a potential vorticity tendency (PVT) diagnostic framework for understanding TC motion. One advantage is that this PVT concept does not involve the coupling mechanisms. Basically, a TC will tend to move towards the region with maximum PVT. The current study represents an attempt to apply this PVT concept to investigate through observational analyses how a non-barotropic (or baroclinic) process, the diabatic heating (DH), affects TC motion because DH contributes towards a positive PVT. A preliminary observational study is performed to see whether TC motion can be related to the convection around the TC center. Analyses of radar imageries from U.S. aircraft reconnaissance in the Atlantic confirmed that convection does play a role in TC motion. About 300 cases among 31 western North Pacific typhoons and tropical storms for the years 1995 - 98 are selected for the analyses. The statistical results show that in only -21% of the cases is the TC motion governed by steering. The DH dominates TC movement in -7% of the total sample. Other than cases in which the steering was difficult to define, the movement of the TCs in most of the remaining cases (except for -10%) can be explained by a combination of steering and DH. Therefore, TC motion is not only governed by steering but also influenced by other physical processes such as DH. In some cases, the DH can be the main contributor to TC motion especially when the steering is weak. A general result is that a combination of steering and DH is a better estimate of TC motion. Analyses .of individual cases further suggest that a TC can either move along the direction pointing towards the highest PVT contributed by the DH. Sometimes, the movement of a TC will follow the rotation of the highest DH contributed PVT when the DH is the main contributor to its motion. Some special cases show that a TC may not necessarily move with the steering flow even though the steering is strong (>l0 kt). The study points to the importance of non-steering processes such as DH in TC motion and provides a new perspective for understanding TC motion.
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