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.