冬季東北季風影響下之台灣北部異常降水之初步研究

A Preliminary Study of Abnormal Rainfall over Northern Taiwan under the Northeast Monsoon Influence in Winter Season

陳泰然(George Tai-Jen Chen) ； 李金萬(Chin-Wan Lee) ； 劉廣英(Koung-Ying Liu)

《大氣科學》 7卷1期 (1980/05) Pp. 73-84

摘要

本文係針對1979年12月15～17日台灣北部地區在東北季風控制下之強烈中幅度降水（日降水量～100公厘）個案之初步分析研究。結果顯示，強勁持續之東北季風經黑潮獲得充沛水氣。潮溼空氣抵達北部地區後，經由邊界層之局部輻合上傳。局部輻合作用主要係由海陸摩擦差異以及局部環流與東北季風之交互作用提供。700 mb以下之低對流層內盛行之暖平流與正渦度平流向上增加，提供了熱力與動力強迫上升運動。上述條件加上低對流層之不穩定大氣，結果導致持續性的中幅度強烈降水。台灣東部沿海亦似北部地區，近地層有局部輻合亦有降水現象。西部沿海則相反，近地層有局部水平輻散，故僅有低雲或晴空。

並列摘要

A preliminary analysis is carried out for a mesoscale heavy rainfall case (daily total ~ 100 mm) under winter northeast monsoon regime over northern Taiwan during the period of December 15-17, 1979. Results show that the high moisture content air over northern Taiwan was continuously supplied by the persistent and strong northeast monsoon passing over the warm Kuroshio current. The local horizontal convergence responsible for upward transport of moisture in the boundary layer was mainly provided by the differential friction between land and sea and by the interactions between local circulation and large scale northeast monsoon flow. In the lower troposphere below 700 mb, warm advection and upward increase of cyclonic vorticity advection provided thermo dynamical and dynamical forcing for upward motion. These together with the potential instability in the lower troposphere, led to a persistent and heavy mesoscale rainfall phenomenon.Similar situation with local horizontal convergence in the boundary layer and rainfall was found over eastern Taiwan. In contrast, local horizontal divergence prevailed in the boundary layer along western coast of Taiwan, thus, low clouds or clear skies were observed.