- 期刊
華南地區梅雨鋒面之特性分析
On the Characteristic of Mei-Yu Front in the Southern China Area
摘要
本文利用FGGE Level III之網格點資料選取1970年華南地區梅雨季中兩個雨量較大的個案作為分析對象，進行梅雨鋒面之特性及周圍環流的分析探討。結果顯示華南地區梅雨季節時，梅雨鋒面的特性為低層有明顯的相當位溫梯度，含有豐富的水汽，鋒面之位置與低層之風切位置吻合，為氣旋式渦度區及上升運動區。鋒面之高層伴有西風噴流，此噴流移至日本附近梅雨槽南方時風速達最大，沿鋒面則伴有類似低層噴流的強風帶。500 hPa之風場顯示在西藏高原的北方有北支噴流、而南方並沒有明顯的噴流存在。由南北向之垂直剖面分析顯示，鋒面以南為對流不穩定區，且對流作用將低層大氣帶往高層，造成的大氣之垂直混合現象。鋒面及其以南為上升運動區，鋒面以北為下降運動區，形成熱力直接環流。用相當位溫梯度來估計的鋒生趨勢，可對梅雨鋒之生成及發展作較正確的估算。由分析顯示，在梅雨鋒面形成後變形項為維持鋒面發展及滯流最主要的影響項。
關鍵字
梅雨鋒面並列摘要
By utilizing FGGE level-III grid-point data, two Mei-Yu fronts with heavy rainfall are selected to study the characteristics of Mei-Yu front in the southern China area.Results show that, during Mei-Yu season of the southern China area, Mei-Yu from has significant equivalent potential temperature gradient. The front coincides with the low-level wind shear, has cyclonic vorticity and upward vertical motion. In association with the Mei-Yu front, there exists in the upper level a westerly jet stream to the north of front and in the lower level strong wind similar to low-level jet along the front. The 500 hPa wind analysis also depicts that the northern branch of middle-level jet to the north of Tibet Plateau still exists. The north-south vertical cross section analyses show that the lower troposphere is convectively unstable to the south of front with upward vertical motion in the areas along and to the south of front, and downward vertical motion to the north of front. Frontogenesis analyses computed with equivalent potential temperature demonstrate that deformation is the most significant effect in producing positive frontogenesis after the formation of Mei-Yu front.