研究生: |
李名翔 Li, Ming-Siang |
---|---|
論文名稱: |
臺灣北部梅雨季極端降水個案之系集分析與可預報度研究 Ensemble-based Analysis and Predictability of An Extreme-precipitation Event over Northern Taiwan in the Mei-yu Season |
指導教授: |
王重傑
Wang, Chung-Chieh |
學位類別: |
碩士 Master |
系所名稱: |
地球科學系 Department of Earth Sciences |
論文出版年: | 2020 |
畢業學年度: | 108 |
語文別: | 中文 |
論文頁數: | 190 |
中文關鍵詞: | 梅雨鋒面 、臺灣北部極端降雨 、技術得分 、系集敏感度分析 、可預報度 |
DOI URL: | http://doi.org/10.6345/NTNU202001022 |
論文種類: | 學術論文 |
相關次數: | 點閱:153 下載:45 |
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本研究針對2017年6月初的梅雨個案,並著重於6月2日當日北部地區的極端降雨事件,進行系集敏感度分析(ensemble sensitivity analysis, ESA)與可預報度的探討。該事件在短短12小時的最大累積雨量就達到641毫米的驚人雨量,並造成北部地區多處產生積、淹水現象。但在事件發生前,多數的數值模式都無法很好掌握北部地區的極端降雨,嚴重低估雨量,不利於事前的防災準備。
本研究採用45個成員的系集預報,透過5種技術得分(TS、BS、POD、FAR、FSS)的計算,來評估各成員的表現。結果顯示相較於24小時累積雨量,12小時累積雨量的得分都較低,且北部地區BS得分大多小於1(預報不足),顯示模式對於北部的短時強降雨較難以掌握,可預報度偏低。
而在系集敏感度分析方面,選取北部地區(東經120.9-122.1度,北緯25.0-25.5度)的平均6小時累積降雨量(6月2日0300-0900 LST)當作反應函數(response function)的結果顯示,影響北部地區降雨的因子主要有(1)鋒面位置和移速(2)鋒面強度(3)環境水氣含量(4)低壓擾動(5)中低層槽線,而這些因子彼此之間也互相影響。中低層槽線的位置與移速會影響到地面鋒面的位置和移速,進而導致主要降雨位置的差異,而低壓擾動的生成與發展又與對流密切相關,當低壓擾動生成後,除了會改變降雨位置的分布,也有助於將鋒後冷空氣帶至較南邊的位置,若鋒面因此南移至臺灣西北近海一帶,再配合地形阻擋使得海峽西南風增強,讓此區域的輻合作用增強,此區域恰好為北部地區降雨的上游位置,加上因輻合而加強的鋒生作用,使鋒面強度增強,而鋒生作用又會影響到鋒面的移動速度,使鋒面移動速度較慢並增強對流發展,造成北部地區產生較多的降雨。
透過高解析度實驗,顯示了提高模式的解析度是有助於改善此極端降雨事件的預報結果。另外,初始與邊界條件的品質好壞對於模式結果也有重大影響。當初始與邊界條件能較好地反映真實大氣的情況時,模式才較有機會能預報出較好的結果,進而提高可預報度。
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