西太平洋-南海地区潜热通量长期变化趋势的南北差异及成因分析

利用1958~2014年美国伍兹霍尔海洋研究所客观分析海气通量项目(OAFlux)的月平均潜热通量和相关气象要素数据,以及NCEP/NCAR再分析表面气压数据,通过Trend-EOF分析方法,本文研究了西太平洋—南海地区潜热通量的长期变化趋势。发现西太平洋—南海地区潜热通量整体呈上升的趋势,其中冬季上升趋势最强。冬季潜热通量趋势存在明显的南北差异,特别是在南海地区,南海北部为上升趋势而南部为下降趋势。南海北部以及菲律宾海地区冬季潜热通量上升的主要原因是海气比湿差的增大,而南海南部潜热通量呈下降趋势,在东侧主要原因是风速减小,在西侧主要原因是海气比湿差减小。南海潜热通量长期趋势的南北差异是风速和海气比湿差的共同作用造成的。另外,研究发现风速变化趋势受到局地环流变化的影响,在表面气压下降中心线以北地区为上升趋势,在其以南为下降趋势,而海气比湿差的变化趋势则主要取决于海表温度的变化趋势。

The North-South Contrast of Long-term Trend of Latent Heat Flux inWest Pacific-South China Sea and the Possible Mechanism

Using the monthly latent heat flux data and relevant meteorological variables for the period of 1958 to 2014 produced by the Objectively Analyzed Air-Sea Fluxes project (OAFlux) of the Woods Hole Oceanographic Institution, and surface pressure data extracted from NCEP/NCAR reanalysis data, the authors investigate the long-term trend of latent heat flux over the West Pacific-South China Sea (WP-SCS). The method of Trend-EOF is applied in this study. An increasing trend of latent heat flux is found when the entire area is taken into account as a whole, especially in the winter. A north-south contrast of latent heat flux changing trend in the winter is noted, especially in the SCS where an increasing trend occurred in the north and a decreasing trend occurred in the south. The increasing trend of latent heat flux in the Philippine Sea and northern SCS is primarily attributed to an increase in the air-sea humidity difference. The decreasing trend of latent heat flux in the southwestern SCS is resulted from a decrease in the air-sea humidity difference, while in the southeastern SCS it is a result of the decrease in wind speed. Air-sea humidity difference works together with wind speed, leading to the north-south contrast of long-term changing trend. In addition, the trend of wind speed is closely associated with changes in surface pressure, while the trend of air-sea humidity difference is associated with changes in sea surface temperature.