舟山海域夏季上升流的年际变化及其与ENSO的关系

The interannual variation of summer upwelling in Zhoushan Islands and its relationship with ENSO

本文利用1968—2021年的海表温度和风场数据,分析舟山海域夏季上升流强度的年际变化,并结合同期的Ni?o 3.4指数分析ENSO(El Ni?o-Southern Oscillation)对上升流的影响。温度和风上升流指数表明,1982—2021年夏季舟山海域上升流均呈下降趋势,下降速率分别为0.062℃·10a^(−1)和0.35m^(3)·s^(-1)·(100m·a)^(-1)。近年来,沿岸风应力的减弱是影响温度上升流指数减弱的一个重要因素。统计更长时间段内(1968—2021年)El Ni?o和La Niño年风上升流指数的强度发现,El Ni?o年平均风上升流指数较小,仅为-10.33m^(3)·s^(-1)·(100m)^(-1)。La Niño年平均风上升流指数较大为7.60m^(3)·s^(-1)·(100m)^(-1),高于El Ni?o和气候态,且多达4级(比例为75%)。进一步分析ENSO与舟山海域风上升流指数的关系发现,ENSO主要通过影响风的变化进而影响上升流的强度。El Ni?o年,舟山海域东南风减弱,导致上升流强度较弱,甚至发生下降流。La Niño年主要为偏南风且风速较大,更有利于上升流的发展。

Based on the sea surface temperature and wind data from 1968 to 2021,this paper analyzes the interannual variation of upwelling intensity in Zhoushan in summer,and the impact of El Niño-Southern Oscillation(ENSO)on upwelling.The temperature and wind upwelling indices both show that the upwelling in Zhoushan sea decreased in summer during 1982—2021,with the decreasing rates of 0.062℃·10a^(−1)and 0.35 m^(3)·s^(−1)·(100m·a)^(-1),respectively.Recently,the weakened coastal wind stress causes the temperature upwelling index to decrease.According to the results,the wind upwelling index during La Niña events is larger than that during El Niño events and climatology.Further analysis of the relationship between ENSO and the wind upwelling index shows that ENSO affects the intensity of upwelling mainly by influencing the wind.In El Niño events,the southeast wind dominated Zhoushan sea weakens,leading to a decreasing upwelling intensity.While in La Niña events,the enhanced south wind benefits the development of upwelling.