Dynamical and climatological characteristics associated with tropoical cyclone size

• Main Author: Liu, Kin-sik (廖健錫)
• Format: Thesis
• Language: English
• Published: Dept. of Physics and Materials Science, City University of Hong Kong 1999
• Subjects: Climatology; Cyclones > Tropics; Dynamics; Pacific; North Atlantic
• Online Access: http://hdl.handle.net/2031/3982; http://lib.cityu.edu.hk/record=b1492534

This study attempts to study the climatological and dynamical characteristics associated with tropical cyclone (TC) size. The size of a TC is defined as the mean radius at which the relative vorticity decreases to 1x10- 5 s- 1 from the centre. The TCs occurring between 1991 and 1996 over the western North Pacific (WNP) and the North Atlantic are included in the study. The satellite-derived wind data from the European Remote Sensing satellites 1 and 2 (ERS-1 and ERS-2) are used to estimate the TC size. The UK Meteorological Office (UKMO) operational analyses are employed to identify the synoptic patterns around the TCs and to calculate the angular momentum (AM) transports associated with the TCs. The climatology of TC size is first investigated. Then the AM transports associated with the TCs are computed to examine their possible relationships with TC size. Finally, the synoptic patterns associated with small and large TCs are investigated. The ERS wind data are demonstrated to be useful in the study of TC size. It is found that the average size of the TCs is larger in the WNP than in the North Atlantic by about 0.7' latitude. Moreover, the mean TC size in the WNP is found to vary seasonally, being larger during the late-season (October and November) and smaller during midsummer (July and August). To understand the physical processes governing TC size change, AM transports associated with the TCs are examined. Composite and case studies suggest that an import of AM into a TC is one of the physical processes governing the size change of the TC. It is also observed that if the AM import in the synoptic environment is large and exceeds the import of AM in the TC circulation by a large amount, growth of the TC is favoured. In contrast, if the AM import in the synoptic environment decreases significantly, the TC will most likely not to grow or even decrease in size. Examination of the 850-hPa flow patterns surrounding the TCs suggests that characteristic synoptic patterns can be identified with TCs of different sizes. For example, the southwesterly surge and late-season synoptic patterns are related to large TCs while the dominant ridge and monsoon-gyre synoptic patterns are favourable for the occurrence of a small TC. The imports of AM in the synoptic environment associated with the first two synoptic patterns are found to be significantly larger than those of the latter two synoptic patterns. This is consistent with the hypothesis that an import of AM may lead to the growth of the TC. CityU Call Number: QC942.L58 1999 Includes bibliographical references (leaves 80-82) Thesis (M.Phil.)--City University of Hong Kong, 1999 xvii, 82 leaves : ill. 30 cm.