影响南海混合层盐度季节变化的因素分析

Factors Influencing the Seasonal Variations of Mixed Layer Salinity in the South China Sea

通过对1950-2012年的南海混合层盐度数据进行分析,发现影响南海北部和南部盐度季节变化的最主要因素存在很大的差异。在南海北部,影响混合层盐度季节变化的最主要因素是蒸发降水,其次是水平平流。随着逐步南移,蒸发降水对盐度季节变化的影响递减,水平平流的影响逐渐增大;而在南海南部,水平平流的作用超过蒸发降水成为影响盐度的季节变化的最主要因素。在整个南海区域,冬季海水垂直混合变强,混合层变厚,下层高盐海水进入混合层,使混合层海水盐度变高,从而对冬季海水盐度的上升趋势产生促进作用;夏季南海北部混合层底存在上升流,南海东南部由于Ekman输运导致混合层变厚,都会将混合层以下高盐海水带入混合层,使混合层海水盐度变高,从而对夏季海水盐度下降趋势产生阻碍作用,但垂直混合对盐度季节变化的影响不大,远小于蒸发降水和水平平流。

By analyzing the data of mixed-layer salinity measured in the South China Sea （SCS） from 1950 to 2012, it is found that the most important factors that influence the seasonal variations of mixed-layer sa- linity differ greatly in the northern SCS from those in the southern SCS. In the northern SCS, the major factor is Evaporation-Precipitation （E-- P）, followed by horizontal advection~ whereas in the southern SCS, the action of horizontal advection becomes the major factor affecting the seasonal variations of mixed- layer salinity, showing that the influence of E--P on the seasonal variations of mixed-layer salinity decrea- ses and the affection of horizontal advection increases gradually from north to south in the SCS. The verti- cal turbulent entrainment can make the mixed layer salinity increase both in winter and in summer, thus promoting the seasonal salinity variation in winter and restraining the variation in summer. However, the vertical turbulent entrainment has slight influence on the seasonal salinity variation, at least far less than the E--P and the horizontal advection.