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Title: | 颱風環境下臺灣地形特徵與降水強度之關係研究 Observational Relationship Between The Precipitation And Terrain Features Over Taiwan In The Typhoon Environment |
Authors: | Jia-Cheng Syu 許家誠 |
Advisor: | 游政谷 |
Keyword: | 颱風降水,平地降水加強,河谷降水加強,舉升凝結機制,種饋機制, Typhoon precipitation,Plain precipitation enhancement,Valley precipitation enhancement,Upslope lifting,Seeder-feeder mechanisms, |
Publication Year : | 2018 |
Degree: | 碩士 |
Abstract: | 本研究利用台灣都卜勒雷達觀測資料與地面雨量資料來檢視在颱風環境下複雜地形與降水強度(分佈)的關係,根據先前研究指出在颱風環境下迎風坡處常有地形舉升加強降水,但是有些颱風的強降水發生卻是在平地或河谷地區,希望透過長期觀測統計來嘗試了解平地及河谷地區發生強降水的頻率,探討當中降水加強物理機制。
統計分析1997~2016年中央氣象局有發布海上警報之颱風(共95個),結果顯示約有76.8%的颱風個案主要強降水發生在山區,20%的颱風個案強降水發生在平地,然而只有3.2%颱風個案強降水同時發生在山區和平地。主要強降水發生在平地的個案中絕大部份是屬於輕度颱風和中度颱風。另外,平均降水強度在低地形高度(0~1公里)的坡度較敏感,而在高地形高度(1~4公里)的坡度則較不敏感。 為了拓展河谷地形降水加強的知識,我們選取臺灣西南部位曾文水庫的河谷為降水分析區域,結果顯示河谷有明顯的強降水發生且河谷內的降水強度明顯大於兩側山脊的降水強度。若更進一步將颱風個案依據降水分佈類型分類,約有56%的颱風個案在河谷會有強降水發生且其上游風場的風向約略平行於河谷的走向,而有44%的颱風個案在河谷沒有強降水發生且其上游風場的風向較不平行於河谷的走向,顯示河谷加強降水的效應與地形上游風向密切相關。 此外,選擇2009年莫拉克颱風個案做個案分析,並且嘗試釐清河谷降水加強的機制。透過多都卜勒雷達風場反演技術得到位於柳藤談峽谷地區的三維風場,從平均輻散場中可以發現在河谷內有明顯的輻合區,且此輻合的來源是因為氣流受到兩側山脊偏折產生的側向輻合。另外,河谷降水加強與河谷內的輻合及垂直速度有明顯的相關性,而跟斜坡舉升凝結機制和颱風背景降水及種饋機制之間的相關性則較不明顯。 This study uses long-term surface and radar observations to analyze the relationship between the precipitation and terrain features as typhoons influence the Taiwan area. In the typhoon environment, the precipitation enhancement over mountains through upslope lifting is well known. However, experience indicates that typhoon-induced heavy precipitation sometimes can be concentrated on the plain areas or the valley regions, which cannot be simply explained by the upslope forcing. The particular aim of this study is not only to investigate the frequency of occurrence for these two types of typhoon precipitation but also to explore knowledge regarding the spatial variability of typhoon precipitation and its possible mechanisms over the complex terrain. Statistical analyses from 95 typhoons during 1997-2016 show that there are 76.8 (20)% of the typhoon cases whose intense precipitation occurs primarily over mountainous (plain) areas and 3.2% of the typhoon cases have no obvious difference in precipitation intensity between mountainous and plain areas. For cases with precipitation concentrate on the plain area, they are often associated with weak or moderate typhoons. In addition, the precipitation intensity is more sensitive to slopes of lower terrain. On the other hand, this study investigates the distribution of precipitation intensity over southwestern Taiwan for 50 typhoon cases during 1997~2016. Statistical analysis indicates intense precipitation is concentrated on the valley regions, with more than a half of typhoon cases whose precipitation occurrs primarily over the valley region. Especially, low level upstream winds associate with valley enhancement cases are often characterized by southwesterlies. As an extreme example, Typhoon Morakot (2009), the valley enhancement of precipitation occur as upstream wind directions are more parallel to the valley and there are strong updrafts and convergence along the valley. According to the correlation coefficient analysis, the enhanced precipitation observed is closely related to the convergence and updrafts within the valley but is less related to upslope lifting or seeder-feeder mechanisms. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/71003 |
DOI: | 10.6342/NTU201802088 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 大氣科學系 |
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ntu-107-1.pdf Restricted Access | 9.52 MB | Adobe PDF |
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