夏季浙江沿岸上升流的年际变化研究

Interannual Variation of Coastal Upwelling in Summer in Zhejiang, China

本文基于JCOPE2数据,综合上升流面积和冷中心强度两方面提出了一个无量纲的上升流强度指数NUI,并以此分析了夏季浙江沿岸上升流强度的多年变化,发现24年来夏季浙江沿岸上升流强度以3和8年为主的周期震荡变化,并有减弱趋势。这与夏季风向与岸线偏离角度的增大密切相关,而台湾暖流的调制作用则是次要因素。机制分析表明,厄尔尼诺现象通过影响风和台湾暖流的年际变化从而影响上升流强度的变化:厄尔尼诺年浙江近岸夏季风速较小,风向偏离岸线角度较大,同时台湾暖流较弱,因此上升流偏弱;拉尼娜年各因素呈相反变化,上升流较强。

Based on JCOPE2 datasets, a dimensionless upwelling intensity index(NUI) is proposed, which combines the area of upwelling and the intensity of cold center. This index(NUI) can describe the strength of upwelling more comprehensively. According to NUI, the multi-year variation of upwelling intensity along Zhejiang coast in summer is analyzed. The index of upwelling intensity(NUI) has shown a three-year and eight-year oscillation with a decreasing trend during 1993 to 2016, closely related to the increasing deflection angle of prevailing wind direction from shoreline,the modulation of Taiwan warm current is the secondary factor. The main factors for long-term variation of upwell intensity are the interannual variability of wind field and Taiwan Warm Current(TWC), both of which are influence by ENSO. In the El Nino years, the wind speed in Zhejiang coastal area is abnormally lower, with a larger deflection angle, and shoreward component of TWC is also abnormally weaker than climatological mean, all of which leads to a weaker coastal upwelling. In the La Nina years, the wind speed in Zhejiang coastal area is abnormally higher, with a smaller deflection angle, and shoreward component of TWC is also abnormally stronger than climatological mean, which leads to a stronger coastal upwelling.