南海夏季風肇始早晚與台灣梅雨季（五、六月）乾濕關係之探討

A Study on Relationship of the Onset Dates of the South China Sea Summer Monsoon and Taiwan Precipitation in the Mei-Yu Season

盧孟明(Mong-Ming Lu)

《大氣科學》 26卷2期 (1998/06) Pp. 205-225

摘要

本報告藉由分析40年的南海季風肇始早晚與台灣梅雨季中的月雨量和季雨量多寡特徵，釐清南海夏季季風肇始時間早晚與台灣梅雨季之乾濕的對應關係。台灣四個氣候代表站降雨資料按百分排序分為偏乾、正常、偏濕三類；南海季風肇始時間依序分為偏早、正常、偏晚三類。南海季風肇始時間早晚乃是分別根據外射長波輻射、垂直風切與低層渦度三種指標獨立判定。分析結果顯示，台灣梅雨季異常降水有明顯的小區域不均勻性，亦即四個氣候代表站彼此之間出現相同降雨類別的機率並不高，其中又以東部與其他區域的差異性最大。這種差異在五月要比六月明顯。四個代表站當中，南海季風肇始時間的偏早或偏晚與東部的梅雨季乾濕特徵關係最清楚。南海季風肇始偏早時，東部的五月與梅雨季偏乾的機會甚小；季風肇始偏晚時，則東部的五月與梅雨季偏濕的機會很小。另外，在東部五月偏乾的條件下，南海季風肇始時間傾向於偏晚。是以，若能對南海夏季季風肇始時間作短期氣候預報，應有助於預報東部的梅雨季乾濕趨勢。另一方面，梅雨季的月或季雨量的異常偏濕與南海夏季季風肇始時間偏早或偏晚並沒有明顯關係。由此可推論造成台灣梅雨季的月雨量或季雨量偏多的因素當中，南海夏季季風肇始時間的異常與否並不特別重要。

關鍵字

梅雨季氣候 ； 南海夏季季風肇始 ； 台灣短期氣候預報

並列摘要

The corresponding relationship between Taiwan Mei-Yu precipitation and the onset dates of the South China Sea summer monsoon is studied by analyzing 40 year data. The precipitation is categorized to three classes: wet, normal and dry. The onset dates are also categorized to three classes: early, normal and late. The precipitation categories are respectively based on the monthly and seasonal total precipitation of four climate representative stations of Taiwan. The onset date categories are based on three onset indices, namely OLR index, vertical wind shear index and low-level vorticity index. The onset categories are independently classified based on these indices. Our results suggest that the distribution of the precipitation categories among the representative stations is clearly inhomogeneous. The probability that two stations, in particular the one in the east and the others, have same precipitation category is low. This regional difference is more clearly reflected on May precipitation than June. The systematic relationship between the eastern Taiwan precipitation and onset dates is most clear. When the onset date is earlier than normal, the eastern part of Taiwan tends to be wet in May or on the base of the entire Mei-Yu season; when the onset date is late, it tends to be dry. Our results also suggest that if the total precipitation of May or Mei-Yu season is less than normal in the eastern part of Taiwan, the onset date tends to be late. Therefore, if the onset dates can be predicted one season ahead, the prediction should be useful for the precipitation seasonal forecast for the eastern part of Taiwan. However, how extreme a wet season can become is difficult to estimate. On the other hand, we did not find any systematic relationship between the wet months or seasons and the onset dates of the monsoon. It is suspected that anomalous wet conditions of Taiwan do not have much to do with the onset time of the South China Sea summer monsoon

並列關鍵字

Mei-yu climate ； South china sea monsoon onset ； Taiwan short term climate prediction