1990年六月九日北部地區豪雨個案的綜觀環境及降水分析

Analysis of Synoptic Environment and Precipitation Characteristics for Heavy Rain Case on 9 June, 1990

鄧財文(Tsai-Wen Deng) ； 陳景森(Ching-Sen Chen) ； 陳台琦(Tai-Chi Chen Wang)

《大氣科學》 20卷2期 (1992/06) Pp. 97-118

摘要

1990年6月9日早晨臺灣北部地區發生豪雨，本研究收集諸如地面、探空與衛星等綜觀觀測和傳統雷達回波資料，以分析豪雨發生前之綜觀環境特徵及豪雨發生當時之降水回波特性。研究結果顯示，近乎滯留之大尺度鋒面帶的強迫抬升作用在豪雨之產生上扮演非常重要的角色。由於槽前的西南噴流帶來暖溼空氣而產生有利於深對流發展之環境，同時配合低層強烈水平水汽輻合與高層輻散及分流的垂直結構，故在鋒面之強迫舉升作用下，於噴流入區左方逐漸發展成豪雨雲系。此一中尺度對流降水系統伴隨地面鋒進入臺灣北部地區後便緩慢南移，因此帶來大量降水而造成豪雨。從雷達回波資料分析發現，強降水一直沿著鋒面帶產生，而且因為鋒後不斷有向後生長（back building）的新生對流胞移入興老舊之主回波帶合併，一方面使後者得以維持並繼續成長，另一方面則使得開口向西南之Y字形回波結構一再反復出現，這是伴隨此次豪雨最特殊的雷達降水回波特徵。當上述降水系統進入臺灣西北沿岸地區後，因受鋒面滯留影響而移動緩慢，使其通過之時間增長，故為北部地區帶來豪雨。

關鍵字

梅雨 ； 中尺度對流系統 ； 向後生長

並列摘要

Heavy rainfalls occurred in the northern Taiwan area in the morning of 9 June, 1990. In order to understand the synoptic environmental conditions associated with mesoscale convective systems (MCSs) and precipitation features during the heavy rainfalls, surface and upper-air observations, IR satellite pictures and traditional radar echo data were used for detailed diagnostic analysis.Results indicated that the forced lifting of nearly stationary synoptic scale front plays a very important role on the occurrence of heavy rain. First, 850mb or 700mb southwesterly LLJ in the pretrough area induced warm moist air to Taiwan Strait and formed a favorable thermodynamic environment for deep convective development. Furthermore, at the left LLJ entrance region, the strong low-level horizontal moisture convergence and upper-level divergence and deffluence provided a good vertical structure, in addition the low-level air was subjected to frontal forced lifting. Therefore, there had a convective cell evoluted into heavy rain cloud system gradually. After this mesoscale convective precipitation system associated with surface front moved into northern area of Taiwan, it moved toward the south slowly and brought a large amount of rain to Taiwan northern area.Radar echo analysis found that precipitation always occurred along the frontal boundary. The strong gust front induced by the mature convection cell at the WSW end would provide new cell evolution to its south side. This back building cell then would be advected toward the north by strong SW flow again and merged with the old dissipated cell so as to form Y shape echo structure, while the direction of this cell motion opposited to the propagation motion of storm would induce a very slow system motion. This is a very special radar echo characteristic associated with the heavy rain event. After that precipitation band moved into Taiwan northwest coast, because of the effect of stationary front, the band moved very slowly toward the south, hence heavy rainfalls took place in the Taiwan northern area.

並列關鍵字

Mei-Yu ； MCSs ； Back Building