在台灣地區，海陸風環流與午後對流發展是夏季天氣日變化的最大特徵，先前許多實驗研究曾針對海陸風現象的時序分布、物理機制、環流結構及與大尺度環流之間的交互作用等主題進行精細的分析，一些針對台灣的研究也提供了海風環流與午後深對流之間關係密切的結果。然而，夏季台灣所面臨的大尺度背景環境具有明顯的季內變化，同時遭受東側太平洋副高與西側南海季風的雙重影響。位於二大系統間的交界地帶，大尺度的背景變化應該深深影響著台灣島內的海陸風與深對流發展。若真如此，則一定會有某種特定的背景環流結構能使海陸風最佳發展。因此首先分析大尺度環流場的氣候特性，定出最適合海陸風環流穩定發展的時節；接著於此時段中嘗試選取一個分類標準，以分類出最能促使海陸風發展，並引發積雲深對流的大尺度流場結構。 於嘗試標準的過程中使用NCEP自1993∼1998年的風場資料，換算成流函數及速度位後，以傅利葉分析濾除季節以上的長週期，再取台灣附近之區域平均值的七月時序分布。選取後分類標準以合成之IR波段衛星雲圖及全島合成測站風場來進行確認。最後訂出的分類標準為：以850mb y呈現反氣旋式結構為基準，尋找200mb y為反相位之氣旋式結構的情況，以確保晴朗的環境；再加入200mb y亦呈現同相位之反氣旋結構但強度更高的考量。 結果顯示： ? 由本島測站資料之長期氣候分析證實七月份為台灣地區夏季季風的間歇期。 ? 七月份為台灣地區海陸風結構最顯著的時節。 ? 所選取的分類標準能夠有效濾出適合海陸風發展的大尺度環流結構。 In summer, the land-sea breeze associated with the development of deep cumulus convection in afternoon is the most significant character in Taiwan. A number of previous experiments and studies have analyzed the time series, physical mechanism, structure and the interaction with large scale circulation about the phenomenon of land-sea breeze. They showed that the sea breeze and deep cumulus convection are with fairly strong relationship. However, in summer, Taiwan faces strong intra-seasonal variation of its environmental flow, undergoes the subtropical high and south-west monsoon. In between these two climatologies, the see breeze evolution in Taiwan should be deeply influenced by the background systems. There must be a certain kind of structure of the background circulation that can help the land-sea breeze develop best. Therefore, here we analyzed the climate character of the large-scale background to determine the most suitable season and month. From such the season, we tried to set some criteria to classify the structure for best inducing the sea breeze and deep cumulus convection. We used NCEP wind (u,v) data from 1993 to 1998, totally six years, to translate into streamfunction and velocity potential, performed the Fourier analysis to filter the extraseasonal period out. Then we calculated the area average around Taiwan to get the daily time series of July. The GMS IR image and CWB surface stations' wind are adopted to check the result of our classification by making composites form the selected cases. Our final criteria are: Based on the anticyclone of streamfunction at 850mb, we searched for the cases of cyclonic 200mb streamfunction for the clear condition. In addition, the 200mb streamfunction with the same phase but stronger of the 850mb one are also adopted. The result showed as follow: a. From the analysis of station data, we verify that July is the break of summer monsoon in Taiwan. b. July is the season with the most significant land-sea breeze structure in Taiwan. c. The criteria of our classification can efficiently filter out the large-scale circulation that help the land-sea breeze develop.
