南海夏季风爆发前后南海海温之演变特征

AN ANALYSIS OF SST VARIATION DURING SOUTH CHINA SEA MONSOON ONSET PERIOD IN SOUTH CHINA SEA

利用1983-2002年NCEP/NCAR再分析的周平均海温(SST)场、逐日OLR、风场、海平面气压场、2m高度空气比湿资料,及Woods Hole海洋研究所提供的OAFlux逐日潜热通量和ISCCP(国际卫星云气候计划)逐日短波辐射通量等资料,分析了南海地区季风爆发前后几周的南海多年平均SST随时间的演变和空间分布特征及其物理过程。结果表明:(1)西南季风爆发前,南海全区SST显著升高,其中北部(17°N以北)升温幅度明显大于南部;从季风爆发到季风爆发后1周(季风爆发期),南海全区SST急剧降低;之后几周(季风爆发后),SST变化存在较明显的空间差异,南海北部转为升温趋势,而南部SST持续下降。(2)季风爆发前,短波辐射增加,且南海北部增加幅度大于南部,导致南海SST上升且存在南北不均匀性。(3)季风爆发期间,南海短波辐射急剧减少、潜热通量显著增加以及西南气流的突然增强共同导致SST的下降。(4)季风爆发后,南海北部短波辐射增加而南部减少,对南北SST变化差异的产生有重要作用,同时近地层风场引起的海表动力过程也是影响SST变化的另一重要原因。(5)季风爆发前后短波辐射的变化均和云量多少有关;季风爆发期间的潜热变化在南海南部主要是风速变化的结果,北部海气比湿差的贡献比较大。

Temporal and spatial variations of the weekly mean SST in the South China Sea（SCS） during the SCS monsoon onset period and its physical mechanism have been analyzed by using weekly mean or daily NCEP/NCAR reanalysis data and daily OAFlux latent heat flux data and ISCCP short wave radiation data for the period of 1983--2002. It is found that： before the monsoon onset ,notable warming occurs in the whole SCS, but the range of the North is more significant than the South, then the decrease of SST sweep the whole SCS from south to north rapidly and last about two week. During the following several weeks, the SST variation shows distinct spatial distribution features： The increase of SST in the north and the decrease of SST in the south of SCS appear clearly. The notable warming before the onset of monsoon is associated with the increase of short wave radiation, which is related to the cloud cover. The decrease in SST tendency in the SCS of two weeks following the SCS monsoon onset is due to the reduced short wave radiation, enhanced latent heat flux and boost upped southwest wind, The variations of short wave radiation, and the upper ocean dynamic processes ,which are related to the wind field ,are important impact factors to the distinct spatial distribution features of SST after monsoon onset.