琳恩颱風(1987)與東北季風交互作用產生強降水之研究

A Study on the Heavy Rainfall Due to the Interactions of Typhoon Lynn (1987) and the Northeasterly Monsoon

李清勝(Cheng-Shang Lee) ； 羅英哲(Ying-Zhe Luo) ； 張龍耀(Lung-Yao Chang)

《大氣科學》 35卷1期 (2007/03) Pp. 13-33

摘要

本研究分析與東北季風共伴導致台灣北部豪雨的颱風路徑特徵，結果顯示1987~2000年間，有6個侵台颱風有顯著共伴效應；其路徑可概分為二類，一為由東向西經巴士海峽，另一則為由台灣東方近海北上。在這些颱風中，以琳恩（1987年）之共伴效應最顯著；當其中心位於距台北約500公里時，卻導致竹子湖單日降水量達1,136mm與北市嚴重淹水。因此本研究利用MM5數值模式，模擬、分析琳恩之侵台過程，並探討導致豪雨之重要機制。
分析與模擬結果顯示，琳恩颱風影響期間，台灣北部地區之主要強降水，出現在鋒面由南北退且於台灣北部滯留時，且此顯著強降水並非單純之地形舉升降水。強降水區呈東西向帶狀分布且其中有數個強降水中心。分析環流特徵顯示，強降水區和低層環流輻合區關係密切，故低層颱風外圍環流與東北季風輻合的舉升作用顯著；再者，輻合區中的移動性對流胞與中尺度過程，亦扮演相當重要角色。此外，地形舉升作用則有加強和地區鎖定的作用，當環境風場輻合作用和地形舉升作用一致時，將導致持續性強降水。

關鍵字

颱風 ； 颱風降雨 ； 東北季風 ； 數值模擬

並列摘要

This paper analyzed the tracks of those typhoons which interacted with the northeasterly monsoon and caused heavy rainfall to the northern Taiwan. Results showed that in 1987-2000, there were six typhoons which interacted significantly with the northeasterly monsoon. Tracks of these typhoons could be classified into two types. Typhoons of the first type took a westward track toward the Bashi Channel, and typhoons of the second type took a northward track over the near-shore ocean along the east coast of Taiwan. Among these typhoons, Lynn in 1987 appeared to interact with the northeasterly monsoon most significantly. When the center of Lynn was located at a distance of over 500 km from Taipei, the daily accumulated rainfall at Jhuzihhu reached 1,136 mm, resulting in the severe flooding in the Metropolitan Taipei area. Therefore, we used MM5 to simulation Lynn when it was affecting Taiwan and discussed the important mechanisms responsible for the heavy rainfall.
Results of data analyses and model simulation showed that the heavy rainfall at the northern Taiwan during the typhoon period occurred when the front moved northward and became stationary at northern Taiwan. The heavy rainfall was caused not by the topographical lifting only. The heavy rainfall occurred at an east-west oriented zone with several rainfall maxima. The analysis of the circulation pattern showed that the heavy rainfall area was closely related to the low-level convergence. Therefore, the lifting caused by the low-level convergence of the typhoon outer circulation and the northeasterly monsoon appeared to be quite significant. In addition, the traveling convective cells and the meso-scale process had also played an important role in the generation of heavy rainfall. Finally, the topographical lifting acted to enhance the convection and lock the heavy rainfall area. When the flow convergence effect was enhanced and locked by the topographical lifting, it would produce continuous heavy rainfall.

並列關鍵字

Typhoon ； Typhoon rainfall ； Northeasterly monsoon ； Numerical simulation