副熱帶反流區的渦漩對東海黑潮傳輸量之影響

Abstract

在本研究中，我們使用20年的模式再分析資料來測量當渦漩通過之時，渦漩對黑潮傳輸量的影響。這些渦漩來自於副熱帶反流區，一個斜壓不穩定的區域。在渦漩活躍的時期，上游靠近台灣東部的黑潮較平時還要強，主軸的深度更深，且主軸也較平時往東偏移。研究結果發現，黑潮的傳輸量在暖渦通過時增強，冷渦通過時減弱。此外，在冷渦通過測線的過程中有部分流速及傳輸量增加的情況，而此現象與渦漩穿過測線的位置有關。一般而言，傳輸量的計算須藉由海流兩側的海表面高度差來計算，然而，Gawarkiewicz et al. (2011) 藉由台灣東部外海 (123.2o E,23.9o N) 海表面高度異常值和20個月的觀測資料有良好的相關性提出，使用單一點的海表面高度異常值，能夠表示黑潮的傳輸量變化。為了驗證與說明這個想法，我們由海表面高度資料得知，由於副熱帶反流區渦漩的影響，靠大洋側的變化較靠陸地側的還大，因此黑潮傳輸量(兩側高度差的變化)主要被靠近大洋側的海表面變化影響。接著我們延伸此想法，沿著黑潮取了多條側線。結果顯示在副熱帶反流渦漩的影響區域之內，右側單點的海表面高度異常值變化能夠顯著代表黑潮的變化，指出了渦漩對黑潮變化的重要性。

In this study, 20 years JCOPE2 reanalysis data is used to study the effect of mesoscale eddies on Kuroshio east of East China Sea. These eddies come from Subtropical Counter Current (STCC) region, where is recognized as baroclinically unstable area. In eddy-rich years, the upstream Kuroshio is stronger and deeper. The Kuroshio path also shifts eastward. Generally, the warm eddies increase Kuroshio transport and the cold eddies weaken the Kurshio. However, the exceptions are also observed due to the related location where eddies passed by. According to geostrophic relation, transport is calculated taking the sea surface height difference (ΔSSHA) from two sides of current. Gawarkiewicz et al. (2011) proposed the sea surface height anomaly (SSHA) at (123.2oE,23.9oN) can be the proxy of Kuroshio transport based on the good correlation between the SSHA and 20 months observed Kuroshio transport. We explain their idea and extend the time period using satellite altimeter data. The result shows that the SSHA variability at open ocean side has much greater magnitude than the near-shore side due to the effect of STCC eddies. The Kuroshio transport variation (ΔSSHA of two sides) is mainly influenced by the SSHA on oceanic side, so that the single station can serve as the proxy of Kuroshio transport. We apply this idea along the Kuroshio path. The result shows that single points SSHA variability on the open ocean side can account for the Kuroshio variability in STCC eddy effective area. This results address the importance of eddies on Kuroshio transport.