海面溫度對於臺灣東南沿海對流線之影響

Effect of Sea Surface Temperature on the Convective Lines off the Southeastern Coast of Taiwan

林哲佑(Che-Yu Lin) ； 游政谷(Cheng-Ku Yu)

《大氣科學》 44卷3期 (2016/09) Pp. 215-235

摘要

本研究主要利用綠島C-band都卜勒雷達與MODIS (The Moderate-resolution Imaging Spectroradiometer)衛星資料來探討海面溫度(sea-surface temperature, SST)對於台灣東南沿海對流線之影響。台灣東岸為黑潮主流流域，對於此區域海洋至大氣對流層之熱量及動量傳輸扮演著重要的角色。然而，在此區域的低層大氣與海面溫度(SST)/海面溫度梯度(SST gradient)之交互作用是否會影響中小尺度之對流線（如生成位置與季節）仍為未知，故本研究目的著重於探討台灣東南沿海對流線與海面溫度/海面溫度梯度之間的關係。本研究檢視2002~2004年的雷達資料，共選取出257個對流線個案。統計結果顯示，對流線最常發生之區域是位於離岸10～30 km之沿海地區；海面溫度梯度較大之區域也同樣是集中在離岸30 km以內之沿海地區；而海面溫度較高處則位於離岸40 km以外之外海地區。在季節統計方面，各個季節對流線生成區域與較顯著之海面溫度梯度區域也有著相似的分佈，但與較高海面溫度區域有所不同，顯示海面溫度梯度對於對流線之生成位置可能有所影響。然而，海面溫度較高之區域不論在哪個季節皆與對流 線較常發生之區域有所差異。此外，對流線於冷季（10月～4月）較常發生，暖季（5月～9月）則反之。沿海地區之低層輻合與對流線在不同季節之生成頻率也有著一致性，在平均低層輻合較大的月份，其對流線生成頻率也相對較高。造成低層輻合季節性的變化除了與大環境風場的改變有關之外，海面溫 度梯度可能也有所貢獻。

關鍵字

對流線 ； 都卜勒雷達 ； 海面溫度 ； 海面溫度梯度

並列摘要

This study used C-band Doppler radar on Green Island and Moderate Resolution Imaging Spectro Radiometers (MODIS) nighttime Sea Surface Temperature (SST) derived from satellite measurements during 2002-2004 to investigate the relationship between the convective lines off the southeastern coast of Taiwan and SST. The coastal zone of eastern Taiwan is the main path of Kuroshio, which plays an important role in transports of heat and momentum from ocean to troposphere in this particular geographical location. Whether the interaction between the atmosphere and SST associated with Kuroshio may operate to influence the initiation and intensity of the convective lines remains unknown. The main objective of this study is to explore the possible relationship between the convective lines and SST along this coastal zone. A total of 257 cases of the lines were identified during 2002-2004. Statistical analyses for all identified cases reveal that the area of the most frequent occurrence was primarily confined to an elongated zone located ~30 km off the coast and the locations of the line’s occurrence generally coincided with the regions of obvious SST gradient. However, the areas of warmer SST were located father offshore, greater than 40 km away from the coast and did not coincide with the main positions of the line’s formation. The result also indicates that the lines prevailed in spring and winter, but were much fewer in summer. The low-level convergence in nearshore regions also showed a clear, consistent trend of monthly variation like the lines did. This monthly variation was found to be related to the interaction between the atmosphere and SST gradient associated with Kuroshio.

並列關鍵字

Convective line ； Doppler radar ； SST ； SST gradient