| 摘要: | 台灣受東亞季風影響，在梅雨季(5月中～6月中)適當的綜觀條件下(Chen and Li, 1995)，大雨(時雨率>15mm而且日雨量>50mm )受西南季風及地形的影響，大部分發生於台灣西南側中央山脈的迎風面。 2005年之梅雨季在台灣在西南部的主要豪雨日(台灣西南部至少有5個雨量測站大於130mm/day，而且至少有1個雨量測站大於200mm/day)發生在12～15號之間。這四天在西南部的累積雨量佔05年西南部梅雨季總雨量的50％以上。12號西南部之降雨特性為降雨極值發生在早上8點和下午3點，和其他三天(13、14、15日)不同，6月13號在西南部的降雨日變化早上有一個極值發生在08LST，但午後沒有明顯的極值；14號06LST有一個極值，另一個較大極值在傍晚21LST；15號的極值與12號相似，極值在05LST及15LST，但午後極值比清晨大。又12號發生超大豪雨的測站數是12~15日這四天中最大，因此本篇論文著重於研究6月12號豪雨發生降雨的機制。分析EC(European Center for Medium-Range Weather Forecasts)資料、JMA (Japan Meteorological Agency)日本天氣圖、衛星雲圖及中央氣象局雷達回波得知，12號的鋒面在台灣北部近海。5號在南海西北部有熱帶擾動生成，隨時間向東移動，在11號18LST移至南海東北部，在12號接觸台灣西南部，影響台灣西南部降雨。 12日清晨台灣西南部沿海地區有強回波生成，推論沿海地面有因陸風而產生的離岸東南風和海上盛行西南風輻合。在925百帕有受地形阻擋轉向的南風和盛行風輻合，使得降雨發生在沿海和平地地區。另外由南海東北部及近海降雨系統的移入台灣西南部，使得西南部降雨極值發生時間由沿海向內陸延遲。為了研究西南部降雨雙峰的特性以及更進一步瞭解沿岸及斜坡地區發生豪雨之過程，使用天氣預報模式(Weather Research and Forecasting Model, WRF)，來研究南海東北部降雨系統進入陸地之後受地形影響如何造成沿岸和山坡地區之豪雨。 ; During southeast monsoon, heavy rainfall ( hourly rainfall rate > 15mm and daily rainfall rate > 50mm ) occur frequently in Taiwan Mei-Yu season(mid-May to mid-June) over the windward side of Central Mountain Range (CMR) in southwest of Taiwan under favorable conditions (Chen and Li, 1995). Heavy rainfall day (at the least 5 stations the record daily rainfall accumulation greater then 130mm, and at the least 1 station registers the daily rainfall accumulation greater then 200mm) in southwestern Taiwan occurred during 12~15 June 2005. The total rainfall of these 4 days contributed more than a half of rainfall accumulation of Mei-Yu season in 2005. Characteristic of the precipitation had a pair of rainfall peaks happened in 08LST and 15LST in southwestern Taiwan on 12 June. This is differ from other three days(13~15 June). On 13 June, there was a rainfall peak in 08LST. Afternoon rainfall peak was no significantly. On 14 June, the two rainfall peaks were at 06LST and 21LST. On 15 June, the characteristic of rainfall was similar to 12 June. The rainfall peaked at 05LST and 15LST, but the second peak was higher than in early morning. The number of station with daily rainfall accumulation exceeding 350 mm on the 12 June was greater than other three days. Therefore, in this study we investigate the heavy rainfall case on 12 June 2005. Through the analysis of the European Center for Medium-Range Weather Forecasts (EC) data, the analysis Chart of Japan Meteorological Agency (JMA), Satellite images and radar data form Central Weather Bureau, we found a short-wave trough formed over the northeast of South China Sea on 5 June. It moved northeastward, and caused heavy rainfall in southwest Taiwan. During 12~15 June 2005, Mei-Yu front was located on the offshore of north Taiwan. The heavy rainfall event cause by mesoscale convective systems from the northeastern South China Sea. In this study, there were intense radar echoes formed along the coast in the early morning. There may have convergence in the coast of southwestern Taiwan coast by off shore flow near surface of southwestern Taiwan and the prevailing southwest wind over the ocean. At 925 hPa, because the prevailing southwest wind decelerated and became southerly wind cause by terrain blocking. The convergence between prevailing wind and southerly wind occurred over southwestern Taiwan. Rainfall fell in coast and plane. The peak rainfall moved from coast to slope in the southwest of Taiwan. In order to study the characteristic of double rainfall peak and advance our understanding of the mechanism of heavy rainfall in coast and slope, we plan to use the Weather Research and Forecasting Model (WRF) to serve our objectives. ; 研究期間 9708 ~ 9807 |
