台灣北部地區梅雨季豪大雨天氣型態之合成分析
| Autor: | Yu-Chieh Chou, 周羽潔 |
|---|---|
| Rok vydání: | 2009 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 97 Mei-yu front systems usually form in the area extending from Japan to Taiwan and subtropical China during May and June. This season is called the Mei-yu season. The occurrence of continuous and heavy rainfall has a great relationship with Mei-yu fronts in the Mei-yu season. The rainfall frequently causes severe damages in Taiwan. In this study, heavy rainfall cases occurred in northern Taiwan area (24.18°N) during the Mei-yu season from 1979 to 2007 are selected based on the daily accumulated rainfall data of Taiwan Central Weather Bureau. Major weather systems causing heavy rainfall are identified based on weather maps of Japan Meteorological Agency and reanalysis-II data of National Center for Environmental Prediction/Department of Energy (NCEP/DOE). Composite analysis method is adopted to investigate the characteristics of different types of heavy rainfall cases. Scale separation method is also applied to diagnose the roles of large and synoptic scales of circulation on the dynamic and thermodynamic field as well as precipitation mechanisms. A classification of all heavy rainfall cases is made according to the major weather characteristics with F, J and P represent the Mei-yu front, low-level jet and low-pressure band, respectively. The F type cases are mainly affected by Mei-yu front. For this type, Taiwan locates in the borders of the high pressure in Yellow Sea and the Pacific subtropical high. The accompanied weak low-pressure band and strong wind shear of the Mei-yu front provide a favorable condition in forming the low-level convergence. The FJ type cases are mainly under the influence of the Mei-yu front and low-level jet. The southward movement of the high pressure to the north of Taiwan and the southwesterly flow enhance the wind shear of the Mei-yu front in the northern Taiwan. The strong wind shear provides suitable conditions in causing heavy precipitation. For the FP type cases, Taiwan is covered by a low-pressure zone and affected by an approaching Mei-yu front. The cyclonic circulation associated with the low pressure zone is accompanied with southwesterly flow, which causes strong convergence in northern Taiwan area. The approaching Mei-yu front makes the convergence even strengthened. This provides a favorable environment for heavy rainfall to occur. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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