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| Autor: | Ping-Cheng Lin, 林秉承 |
|---|---|
| Rok vydání: | 2008 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 96 The Mei-Yu season over Taiwan occurs during 15 May-15 June (Chen and Chen 2003). During this period, the region of the South China Sea, the Taiwan Strait, and Taiwan is under the influence of the prevailing southwest or west southwest flow. Taiwan is an island, two-thirds of the island of Taiwan is mountainous. The windward side of Central Mountain Range (CMR) locates at southwest of Taiwan during the Mei-Yu season. The occurrences of maximum heavy rain (rainfall rates > 15 mm and daily accumulations > 50 mm) are over the southwestern lowlands and slopes of the CMR (Chen et al. 2007). During 1997 to 2007, the annual maximum averaged rainfall region of Mei-Yu season locates at slope greater than 0.3 in the region of altitude about 500 meters or 2000 meters. The numerical simulation of effects of orography on a rainfall patterns (Chu and Lin 2000, Chen and Lin 2005, Chen et al. 2007), indicate that Froude number is an important index. The aspect ratio (h/a) affects rainfall patterns (Smith 1979). The slope and aspect ratio of southwest of Taiwan terrain are greater than that of Chen and Lin (2005) at least in an order of magnitude. We use WRF model and ideal sounding data in order to realize the effects of southwest of Taiwan terrain on a moist flow and rainfall pattern. The model result show that low moist Froude number(0.14~0.28) ( ， is wind speed， is 、 is virtual potential temperature， is mountain height), unsaturated moist flow is blocked by southwest of Taiwan terrain and becomes a flow-around regime. When moist flow is saturated, the buoyancy frequency diminish or become negative that moist flow becomes unstable and shift to flow-over regime. When moist Froude number is 0.28 and flow is saturated over slopes, the maximum accumulation rainfall region over the height about 1500 to 2000 meters region. This kind of rainfall pattern is analogous the maximum average rainfall region of Mei-Yu season in 2000 and 2006. When moist Froude number is 0.19 and orographic blocking is evident, the maximum accumulation rainfall region is over the height about 500 meters. This rainfall patterns resemble the maximum average rainfall region of Mei-Yu season in 2001, 2002, 2004 and 2005. When moist Froude number is 0.14 that maximum accumulation rainfall region is over the plain and the height about 500 meters region. The rainfall over plain of rainfall is influenced by the convergence region of west southwest wind and south wind due to flow-around the terrain. The rainfall over the height about 500 meters region is the rainfall grow up at the plain and move inland by northwest wind. This rainfall patterns may resemble the 29-May 2008 over the Pingdong area. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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