• 作者： 陳景森; 林傳堯
• 作者服務機構： 中央大學大氣物理研究所
• 中文摘要： 利用1990到1994年5月及6月的氣象局自動雨量站及正規站的降水資料，研究當綜觀影響較微弱時，在台灣地區產生的降水系統之特性。個案的選擇是若無2個測站的當日降水大於20mm，則此日的降水不列入本研究個案。符合這個條件者共選出34個個案。在34個案中若以時雨量大於15mm生的次數（頻率）來看，高頻率發生在地形為500公尺的高度附近，且從北到南皆有。另外中部高山地區低於1500公尺之地區亦出現高頻率。若以出現的降水頻率和時問的變化來看，在正午剛過，降水發生於從台北盆地到台灣南部的斜坡地，當時間增加時降水發生在台北盆地、中央山脈的斜坡及南台灣。在傍晚時降水可以發生在束部。若以3Km以下的風向來探討風向對降水的影響，則我們發現：當風向為東南風則較高頻率在西北部、中部及南部的500公尺等高線附近。若風向為西南風，則較高頻率在北部及中部500公尺的等高線附近。若風向為南風，則降水在台灣束部及西部皆可發生。我們又利用一個三維有地形的數值模式來研究風向對降水發生的影響。初步的結果顯示風向對模式內降水系統發生的位置有很大的影響。大體上，模擬結果與觀測結果相近，但在束南風的模擬中模式在台灣北部有降水而觀測則無，可能的原因是探空資料的代表性或模式的結構不好所致。
• 英文摘要： For the purpose of studying the precipitation systems occurring in the Taiwan area when synopticforcing was relatively weak, 34 days of data during the Mei-Yu season (May and June) from 1990 to1994 were gathered. These selected data represented the total amount of rainfall greater than 20 mmday-' found at least at two rainfall stations established by the Central Weather Bureau The characteristicof the number of occurrences (frequency) of hourly rainfall where the rate was greater than 15mmhr-' was analyzed. A higher frequency was found in the Taipei basin, in the 500 m altitude area fromnorth to south and in sloped areas below 1500 m in central Taiwan. In the early afternoon, rainfall occurredin the sloped areas from the Taipei basin all the way to southern Taiwan. As the afternoon progressed,a higher frequency occurred in the Taipei basin, in the western slope area of the Central Mountain Rangein central Taiwan, and in southern Taiwan. In the evening, precipitation could also occur in eastern Taiwan.The ambient wind direction (below the 3 km height) influenced the formation of precipitation very much.If the wind direction was from the southeast, a higher frequency of rainfall was found over northwestern,central and southern Taiwan along the 500 m elevation. If it was from the southwest, a higher frequencywas found over northern and central Taiwan along the 500 m elevation. If the wind was from the south,precipitation could occur almost all over the island, both eastern and western Taiwan. A three-dimensionalnumerical model with a terrain following coordinate system was used to study the relationship betweenthe ambient wind and the formation of the precipitation systems. In general, precipitation systems occurringin the Taiwan area for different wind directions were captured in the model. However the precipitationsystems in northern Taiwan were found by the model results to occur with a southeast wind, which onlydid not appear to be the case in the observational data. The ambient sounding used in the model or someinability of the model might have caused this difference.
• 中文關鍵字： precipitaion systems; terrain effect; weak synoptic forcin
• 英文關鍵字： --