臺灣梅雨鋒面之中幅度結構

On the Meso-Scale Structure of Mei-Yu Front in Taiwan

陳泰然(George Tai-Jen Chen) ； 紀水上(Shui-Shang Chi)

《大氣科學》 5卷1期 (1978/05) Pp. 35-47

摘要

本文採用準拉格藍基座標，針對1972－1977年5月15日至6月15日之梅雨期內影響臺灣之29個鋒面系統，進行分析其中幅度結構及伴隨之降水。結果顯示鋒面於臺灣北部時，大雨及豪雨發生之最大機率出現於鋒前100公里至鋒後200公里間，於南部時則發生在鋒前200－300公里處。鋒面對於南部大氣具有減小其潛在不穩定度之效果，但對於北部大氣具有加溫及潤濕作用而未改變其原有之不穩定度。結果亦顯示低層最大風速帶，可能是促成對流作用之原因而非其結果。輻散場與溫度場之結構以及降水分佈顯示鋒面在北部時伴隨有兩個對稱於鋒面之熱力直接環流系統，而於抵達南部時伴隨有兩個大小不同之熱力間接環流系統。對流運動在這些次環流系統之上升處受到加強效果，而於下降處則受到抑制作用。間接環流可能係由對流作用所牽引帶動而來。

並列摘要

A quasi-Lagrangian coordinate, fixed on the moving front, is employed to study the meso-scale structure and the accompanying rainfall of the Mei-Yu front in Taiwan. Analyses are made on the composite structure of 29 Mei-Yu fronts which influenced Taiwan in the period of May 15 through June 15, 1972-1977. Results show that the occurrence of heavy rainfall has the maximum probability in the region between 100 km ahead of and 200 km behind the front over northern Taiwan, arid in the region of 200-300km ahead of front over southern Taiwan.Results also show that the net effect of front in southern Taiwan is to decrease the potential instability of the atmosphere. On the other hand, the front in northern Taiwan is to heat and moisten the atmosphere but does not change its instability structure. Low level wind maximum is suggested to be the cause rather than the effect of the convective motions.The structures of the divergence field, thermal field and rainfall distribution reveal that there are two thermally direct cells of equal size with their ascending branches located over the surface front. As the front moves to southern Taiwan, two thermally indirect cells of different size are found with their descending branches located over the surface front. Convective activities are found to be enhanced over the ascending branches and suppressed over the descending branches of these secondary circulations. The thermally indirect cells over southern Taiwan are perhaps driven by the convective activities as suggested by the rainfall observations.