梅雨季台灣中部地區伴隨中尺度低壓豪（大）雨定量降水之中尺中度氣候研究

A Study on the Mesoscale Climatotogy of Heavy Rainfall and Quantitative Precipitation over Central Taiwan in Association with Mesolows in Mei-Yu Season

陳泰然(George Tai-Jen Chen) ； 王重傑(Chung-Chieh Wang)

《大氣科學》 32卷2期 (2004/06) Pp. 117-140

摘要

本文以中尺度氣候觀點，利用1993-1998年5-6月地面降雨資料，分析梅雨季西北與中部沿海中尺度低壓旋生前後，中央山脈以西之中部地區（台中至台南縣，即Post-TAMEX分區5-10）各分區之各型豪（大）雨出現頻率、降雨機率、以及降雨強度之氣候特徵。
結果顯示，西北沿海中尺度低壓（共11個個案）旋生後，在約6-7小時內可使其南側之鄰近分區5-7（台中、彰化、南投）之豪（大）雨頻率與降雨強度，以及中部山區之降雨機率顯著增大。分區5-7的豪（大）雨頻率與降雨強度均在低壓旋生時開始增加，約在3-4小時後達最大；豪（大）雨類型以B型豪雨為最多，但A型豪雨與C型大雨亦可在山區出現；最大降雨強度則介於2.8與3.5 mm h1間。低壓旋生前後之降雨機率上升，以分區6、7、9（嘉義）較大，達25 %以上。同時，降雨強度在分區5-7（即旋生區南側）之增強較旋生區內更大，且以雪山山脈西南側與中央山脈西側迎風面（台中與南投山區）特別明顯。顯然，低壓南側西南氣流之增強，以及山區地形提供舉升條件，可能為導致降雨顯著增大之重要因子。至於分區8-10（雲林至台南縣），則由於距西北沿海低壓較遠，受旋生之影響較不顯著。
在中部沿海低壓（共22個個案）旋生後，一般而言其各項影響均較西北部低壓旋生個案為小，具顯著影響之範圍亦較小，但影響持續時間則較長，可達12小時以上。在豪（大）雨方面，對分區7之影響遠較其它分區顯著，其B型豪雨與C型大雨頻率於旋生後7-8小時突然急速增大，隨即又迅速下降。在降雨強度方面，影響以多山之分區5與7較顯著，最大值亦出現在旋生後7-8小時，強度則可達1.5 mm h1，之後逐漸減弱。旋生前後之降雨機率上升，同樣以山區較大，至少上升15%以上。其餘的分區8-10，則影響有限。降雨空間分佈顯示，低壓旋生後之降雨增加主要亦在雪山山脈西南側與中央山脈西側迎風面（分區5與7之山區），以及分區6之部份平地。另外，低壓南側降雨之增加亦較旋生區內為大。

關鍵字

中尺度低壓 ； 豪（大）雨 ； 定量降水預報（QPF） ； 中尺度氣候 ； 降雨強度 ； 降雨機率

並列摘要

From a mesoscale climatology viewpoint, the present study employed hourly surface rainfall data in May-June, 1993-1998 to analyze the characteristics of rainfall over central Taiwan (forecast areas 5-10 in the 1992 Post-TAMEX experiment) in association with mesolow cyclogenesis over northwestern and western Taiwan. The parameters examined were frequency of heavy-rain events, rainfall probability, and rainfall intensity.
For mesolows over northwestern Taiwan (11 cases), results suggest that both frequency of heavy-rain events and rainfall intensity in areas 5-7, as well as rainfall probability in mountainous regions in central Taiwan are elevated over a period of 6-7 h after cyclogenesis. Heavy rain frequency and rainfall intensity reach their peak at 3-4 h after cyclogenesis, with the majority being type B heavy rain events (and some type A and C heavy rain events in mountainous regions) and a peak intensity between 2.8 and 3.5 mm h1. The increase in rainfall probability associated with mesolow cyclogenesis is greater in areas 6, 7, and 9, all by at least 25 %. To the south of the mesolow (i.e., areas 5-7), the increase in rainfall intensity is greater than within the cyclogenetic region itself, most significantly over mountainous regions in areas 5 and 7. The rainfall amount is raised to the south of the low presumably due to the combined effect of an enhanced southwesterly and topographic uplifting. Effects of mesolows to areas 8-10, on the other hand, are much less significant since these areas are located too far.
The effects of mesolow cyclogenesis over western Taiwan (22 cases) to precipitation are in general weaker with a smaller area of significant influence, but they tend to last longer (for more than 12 h) than those of northwestern mesolows. The influence to heavy-rain events is far more evident in area 7 than all other areas, as frequencies of type B and C heavy rain events increased abruptly at 7-8 h after the cyclogenesis before dropping again. Areas 5 and 7 have the most significant response to mesolows in rainfall intensity, reaching a peak of 1.5 mm h1 also at 7-8 h after cyclogenesis then decreasing gradually. The increase in rainfall probability in association with the mesolow formation is also greater in mountainous areas, by more than 15-20 %. Areas 8-10, again, produce relatively little response. Associated with mesolow cyclogenesis, the rainfall increase is again greater in mountainous regions in areas 5 and 7, as well as some plain regions in area 6. For mesolows to western Taiwan, the increase in rainfall intensity is also greater to the south of the lows, over areas 11 and 12 in southern Taiwan.

並列關鍵字

Mesolow, Heavy rain, Quantitative precipitation forecast (QPF), Mesoscale climatology, Rainfall intensity, Rainfall probability.