利用衛星資料分析台灣東部外海黑潮與大氣之交互作用

Abstract

台灣緊鄰黑潮，眾多天氣系統與黑潮相關，近年針對中高緯度暖流與大氣間交互作用研究眾多，然而目前對中低緯度暖流，特別是台灣東部外海黑潮對大氣的影響程度了解甚少。本研究目的即為探討低緯段黑潮(KS)與大氣間交互作用，研究範圍定在台灣東部外海到琉球群島，利用高解析衛星資料及觀測資料探討多項相關參數，包括海表面溫度、雲量、降雨率、蒸發率、水氣通量、風場輻合、垂直運動、熱通量等，分析季節性變化與單月份年際變化，季節性變化中搭配低緯段墨西哥灣流(GS)比較討論。 季節分析結果顯示，KS區內冬季的黑潮藉可感熱通量和蒸發，對大氣影響為淺層加熱，受大尺度下沉氣流影響，垂直上升運動至750hPa；春季則透過海溫梯度影響低層風場，風場和水氣在當地輻合，並有鋒面抬舉作用，產生深對流以致降雨，垂直上升運動至400hPa；夏秋兩季對流發展強，分別達100hPa和150hPa，但是KS海溫梯度不顯著，主要為溫度夠高所致。GS則四季皆有顯著海溫梯度，冬季情形與KS類似，但無下沉氣流壓抑且和高緯運動相連，可達300hPa；春季蒸發減少，垂直運動只至700hPa；夏秋也和KS同，對流顯著達150hPa和200hPa，不過海溫梯度使上升運動固定於此。黑潮也具年際變化，在2002到2008七年中，因2002年12月海表溫度可至27度，定義為強年，藉由低層風場的調整，對大氣的影響能突破邊界層達中高大氣層(200hPa)，其他年份則如冬季KS的分析。 整體來說，若海表面溫度夠顯著，且大尺度大氣無不利條件， KS在冬季和春季時藉海溫梯度對低層風場的調整，影響可達中高對流層。然而目前分析僅限於觀測資料，確切限制因素和影響機制尚未完全釐清，其他大尺度大氣資訊和模式模擬等方式是值得進一步發展的。

Many weather phenomenons are related to Kuroshio, which is neighboring to Taiwan. However, there were rare studies about the interaction between the atmosphere and the warm current in low latitude region, especially Kuroshio near the east of Taiwan. The aim of this study is to investigate the atmosphere response to the south region of Kuroshio (KS: 118-132oE, 22-30oN) and to compare with the south region of Gulf Stream (GS: 278-292oE, 30-38oN). A suit of high resolution satellite data and observed data are analyzed including sea surface temperature (SST), cloud, rain, evaporation, moisture flux, vertical motion and heat flux etc. Seasonal variability analysis showed that, in winter, KS and GS affected atmosphere by sensible heat flux and evaporation. The upward motion extended from surface to 300hPa in GS, but limited to 750hPa in KS owing to large scale downward motion; In spring, SST gradient was stronger than other seasons in KS and cooperated with frontal lifting. It sequentially caused the local wind convergence, deep convection and rain. The upward motion extended to 400hPa in KS, but to 700hPa in GS; In summer and fall, the upward motion extended to about 150hPa in both KS and GS. In GS, the SST gradient was the key to anchoring the upward motion. In KS, the deep convection was due to high-SST. Additionally, there was interannual variability in KS. During 2002 to 2008, the highest SST (27℃) was in December 2002. Through adjustment of low level wind field, the influence of KS reached to upper troposphere (200hPa). Overall, the KS will affects the upper troposphere through low level wind adjustment by SST gradient in winter and spring, if SST is strong and atmospheric condition is not unfavorable. Our study was based on observed data set, the exact restricted reason and mechanism are not clear, other large scale information and regional model would be good methods to further study.