台灣地區寒潮個案之次環流系統

Secondary Circulations of Cold Surge Cold in the Vicinity of Taiwan

黃鴻榮(Hung-Lung Huang) ； 蔡清彥(Ching-Yen Tsay)

《大氣科學》 10卷1期 (1983/03) Pp. 67-74

摘要

本文分析寒潮爆發期間之200mb速度位分佈與次環流，並比較強寒潮與極強寒潮個案之異同。一般而言，強寒潮與極強寒潮之環流系統是相近似的。在500mb和200mb上，中緯度槽線首先由蒙古地區移入中國大陸。此槽線必須伴隨著斜壓次環流系統。但中緯度槽線在此時並不一定伸展至低對流層（850mb和700mb）。另外，在西藏高原東側亦有槽線形成於850mb和700mb上。中緯度槽線與西藏高原東側槽線終將合而為一，在低對流層由中緯度延伸至華南地區。在地面鋒面通過台灣北部前12小時，寒潮次環流系統之上升運動位於華南地區，在200mb往北流，而在塞北或東北地區有下沉運動。此次環流系統有加強東亞地區local Hadley circulation的作用。極強寒潮與強寒潮之主要不同在於西藏高原東側槽線之結構與伴隨之次環流系統。對於強寒潮個案而言，此槽線是由下沉運動和絕熱增溫所造成，並限於850mb與700mb高度之間。而極強寒潮個案之槽線則可能是由於上升運動與潛熱釋放所造成，此槽線可由850mb向上伸展至200mb高度。

並列摘要

In this study we analyze the distributions of 200mb velocity potential observed during the cold-air-outbreak periods, examine the secondary circulations, and compare their similarities and differences between the extreme severe and severe cold-surge cases.In general, the circulation patterns are similar for the extreme severe and severe cold- surge cases. At first, a 500 and 200mb mid-latitude trough moves into mainland China from Mongolia, and the trough is normally accompanied by a baroclinic secondary circulation system. However, the trough does not necessary extend downward to the lower tropostphere (850 and 700mb) at that time. At the same time, a lee trough forms at 850 and 700mb to the east of Tibetan Plateau. Then, the mid-latitude trough and the lee trough combine into one system and extends to lower troposphere from the mid-latitudes to southeast China. Twelve hours before the front passes the northern Taiwan, the secondary circulation system is associated with rising motions in southeast China, northward motions at the 200mb level, and downward motions in northern or northeastern China. It indicates the strengthening of the northern local Hadley cell.The major differences between the extreme severe and severe cold-surge cases are the structure of the lee trough and accompanying secondary circulations. For a severe cold-surge case, subsidence with adiabatic warming causes the formation of a lee trough. The trough is limited in a layer between 850 and 700mb. As for the other, the upward motions accompany the extreme severe cold surge case during the formation stage. Latent heart release is probably the cause of the formation of the lee trough that extends upward from the 850 to 200mb level in a later stage.