梅雨季台灣北部地區鋒面型與非鋒面型午後對流研究

Frontal and Non-frontal Convection over Northern Taiwan in Meiyu Season

陳泰然(George T. J. Chen) ； 周鴻祺(H. C. Chou) ； 張子琦(T. C. Chang) ； 劉志信(C. S. Liu)

《大氣科學》 29卷1期 (2001/03) Pp. 37-52

摘要

本文利用1991-1996年5-6月民航局中正機場都卜勒雷達回波資料，分析北台灣地區梅雨季不活躍鋒面型與非鋒面型午後對流之氣候特徵。幷利用中央氣象局北台灣地區地面氣象觀測資料，分析此段期間梅雨季北台灣一天內不同時刻之平均風場，以探討午後對流與局部環流之關連。
結果顯示，鋒面型午後對流最初形成於雪山山脈與其西北側山坡之東北-西南走向之帶狀區；非鋒面型相似，但形成頻率較高。鋒面型與非鋒面型午後對流均沿雪山山脈發展，亦均於1500LST最爲活躍，且對流有向西北移動或發展之勢。鋒面型與非鋒面型午後强對流發展分布相似，均爲雪山山脈北側發生頻率較西北側爲高且較早。鋒面型午後强對流有向西北移動或發展之勢，有些則向東北偏移；非鋒面型午後强對流則在雪山山脈西北側，傍晚時有由高山移至山坡或由山坡移至平地之勢，在北側1400-1500LST則有由山坡移至盆地之勢。
在分析時段中，北台灣地區午後均有顯著的海風與上坡風等局部環流發展，且均於台北盆地東南方與桃園大溪附近形成氣旋式渦旋。局部環流伴隨之地形舉升與氣旋式渦旋伴隨之輻合作用，在激發午後對流發展均扮演重要角色。因伴隨非鋒面型之海風與上坡風較伴隨鋒面型者發展較强且較持續，使得非鋒面型之對流發展亦較旺盛。

關鍵字

鋒面型 ； 非鋒面型 ； 午後對流 ； 回波強度 ； 回波頻率 ； 局部環流 ； 氣旋式渦旋

並列摘要

Radar reflectivity data from the Civil Aeronautic Administration (CAA) ground-based Doppler radar and surface observations from the Central Weather Bureau for the period of May-June 1991-1996 were analyzed to reveal the relationship between daytime convection and local circulation under the influence of inactive Meiyu fronts and non-frontal situations over northern Taiwan.
Results show that both the inactive frontal and the non-frontal type convection were first initiated over the northwestern slope of the Snow Mountain Range (SMR). The maximum frequency of convection for both types occurred at 1500 LST to the north and the northwest of the SMR. Although the evolution of them was quite similar, the non-frontal type convection was more active during the analyzed period. After convection initiation, the stronger convection of frontal type appeared to move northwestward and non-frontal type moved from the mountain crests to the mountain slopes or from the mountain slopes to the plain area.
Results also show that the sea breezes, upslope winds, and localized cyclonic vortices prevailed over northern Taiwan. Cyclonic vortices were mainly located over Da-Jen Mountain and Da-Shi. Convective activities were modulated strongly by the local convergence associated with cyclonic vortices and by the sea breeze circulations. Local circulations for the non-frontal type were stronger and persisted longer. AS a result, the non-frontal convection was much more active than that of the inactive frontal type.

並列關鍵字

Frontal type ； Non-frontal type ； Daytime convection ； Echo intensity ； Echo frequency ； Local circulation ； Cyclonic vortices