热带太平洋混合层盐度季节-年际变化特征研究

SEASONAL AND INTERANNUAL VARIABILITY OF MIXED LAYER SALINITY IN THE TROPICAL PACIFIC OCEAN

基于2004年1月-2013年12月的Argo及卫星遥感等观测数据,运用经验正交函数(EOF)方法分析了热带太平洋混合层盐度(MLS)的时空特征并探讨其物理机制。结果表明:热带西太平洋混合层盐度呈现出明显的递增趋势,南太平洋辐合带(SPCZ)区域尤为显著,而南热带太平洋东部的混合层则有变淡的趋势。在季节时间尺度上,MLS在如下的4个区域呈现显著变化:西太平洋暖池、赤道东太平洋美洲沿岸、赤道辐合带(ITCZ)和SPCZ。利用盐收支方程进一步定量分析了两个代表区域(暖池区和ITCZ区)的MLS变化率及其控制因子,研究发现:暖池区淡水通量长年表现为负值,且随季节变化波动不大。除6、7月之外,水平平流对MLS变化率均有正的贡献,其峰期出现在10-12月。ITCZ区的淡水通量存在显著季节变化,其下半年的贡献明显大于上半年,水平平流输送和混合层底的夹卷也在11月达到最大。暖池区的盐度变化主要受到水平平流的影响,混合层底的夹卷作用贡献相对较小,而在ITCZ区混合层底的夹卷贡献作用则更显著。

Based on Argo profiles and satellite remote sensing data during 2004/01 to 2013/12, the seasonal and interannual variability of mixed layer salinity （MLS） in the Tropical Pacific Ocean are analyzed by using empirical orthogonal function （EOF） method, and the physical mechanisms are also discussed. The results show that MLS decreased in western tropical Pacific Ocean but increased in the east of southern tropical Pacific Ocean during the period of this research. Significant seasonal variability was found in 4 regions ： （ 1 ） the western Pacific warm pool, （2） The eastern tropical Pacific, （3） the intertropical convergence zone （ITCZ） , （4） the south Pacific convergence zone （SPCZ）. The MLS budget in two typical regions is investigated by a salinity budget function, which represents warm pool （WP） and ITCZ region. Within an annual cycle, the rainfall is larger than the evaporation in WP region, implying a negative freshwater flux forcing with a subtle variation. Apart from June and July, horizontal advection has a positive effect on the local MLS, and reaches its peak stage during October to December. The freshwater flux has a strong seasonal cycle in the ITCZ region, and its value in the first year is much larger than the second year. In addition, ocean dynamic reaches its maximal in November, which contains horizontal advection and entrainment. Overall, horizontal advection dominants the seasonal cycle of MLS in the WP region, and the entrainment in ITCZ is more significant than in the WP region.