1979年東亞梅雨候平均大尺度環流之變化特徵

Characteristics of 5-day Averaged Large-Scale Circulation over East-Asia during 1979 FGGE Year

周仲島(Ben Jong-Dao Jou) ； 陳泰然(George Tai-Jen Chen)

《大氣科學》 17卷4期 (1989/12) Pp. 303-330

摘要

本文使用1979年FGGE及NASA紅外線長波輻射資料，探討台灣梅雨期東亞地區候平均大尺度環流與對流活動之演化及其相關。結果可摘述如下：（1）6月中旬以前東亞地區主要對流活動，有赤道為中心南北緯各10度區域之雲帶及自日本東方海面往西南延伸至華南、台灣的梅雨鋒面雲帶。印度季風環流於6月下旬建立完成後，各主要對流雲區明顯北移。梅雨鋒面雲帶北移至長江流域，進入長江梅雨期。（2）200毫巴候平均速度位分佈與對流強度指數分佈的演變相當一致。顯示台灣梅雨、長江海雨及印度季風所伴隨之深對流活動對東亞及鄰近地區春末夏初高層大氣環流的演變扮演重要的角色。（3）對流活躍區平均位置在高層西風噴流條入區右側（西南側），顯示高層大尺度輻散場有利梅雨鋒面雲帶内之深對流發展。（4）副熱帶西風噴流在梅雨區内（100-140°E），於對流活動旺盛時有顯著下游加速現象。顯示深對流引發的高層輻散風場有加強噴流條作用，此有利於入區右側高層輻散之維持，為深對流持續發展之有利條件。此種正回饋作用可能為梅雨季對流與環流交互作用之重要一環。（5）東亞地區低層斜壓帶強弱與變形場強度以及對流活躍度有密切關聯，顯示若環境條件有利於梅雨鋒面生成與維持，則亦有利於對流活動的發生。（6）由氣壓指數（PI）的分析，再度發現華南與台灣地區若有顯著源於孟加拉灣或印度洋的西南氣流，則對流顯著；若由太平洋高壓環流所控制，則對流不顯。

關鍵字

候平均 ； 梅雨 ； 大尺度環流 ； 向外長波輻射 ； 全球大氣實驗資料 ； 氣壓指數

並列摘要

In this study, five-day-averaged FGGE and NASA Outgoing Long-wave Radiation (OLR) data were used to study the evolution and the relationship of the large-scale circulations and convective activities over East Asia during Taiwan Mei-Yu season. Results can be summarized as follows:(1) There are two major convective cloud systems over East Asia area during Taiwan Mei-Yu season, the equatorial convective cloud system and the Mei-Yu frontal cloud system. Both cloud systems moved northward after the onset of the Indian monsoon. The equatorial convective cloud system moved to northern India and the Arabian sea and the Mei-Yu frontal cloud system moved to the Young-Tze river and started the Chian's Mei-Yu Season.(2) The velocity potential at 200 mb showed a similar evolution to the convective activity over East Asia. The result suggested that the convective activities associated with equatorial cloud system and Mei-Yu system are important part of the general circulation over East Asia.(3) Some of the active convections was observed on the right-hand-side of the jet entrance region. This seemed to suggest that the large-scale upper level divergent area is favorable for deep convection in the Mei-Yu system.(4) Pronounced downstream acceleration of the subtropical jet was found to have a good relationship with the deep convective activity. A positive feedback process between these two systems was suggested.(5) The intensity of the baroclinic zone and the deformation field over East Asia seemed to have a close relationship. This suggests that environment conditions favorable for the formation and maintanence of the Mei-Yu frontal system are also favorable for the stronger convective activities.(6) From the pressure index (PI) analysis, it was observed that a stronger southwesterly flow from the Bay of Bengal is favorable for stronger convective activity associated with Mei-Yu system.

並列關鍵字

Pentad average ； Mei-Yu ； Large-scale circulation ； Outgoing long-wave radiation (OLR) ； FGGE data ； Pressure index