Air-sea heat fluxes and budget over South China Sea during cold surges in 2008/2009 winter

The significant climate characteristic in the South China Sea (SCS) during winter monsoon is that northeast monsoon is the prevailing wind and cold surges frequently occur.The features of sea-air heat flux and budget during the winter monsoon,especially during the cold surges,were studied,based on the data collected from the sea-air flux experiment in Yongxing Island,SCS,from October 2008 to April 2009.The results showed that:the sensible heat (SH) flux slightly increased during the prophase of winter monsoon with the increase of temperature difference between air and sea s compared to that during summer (southwest) monsoon.The average latent heat (LH) flux during winter monsoon was almost equal to that during the summer (southwest) monsoon.The total solar radiation decreased significantly,and the long wave radiation of the atmosphere also decreased,as a result,the net heat budget of the sea became negative value,which caused the sea surface temperature (SST) dropping after autumn.The SH fluxes during the cold surges were higher than the average flux during the winter monsoon,and before January,most of the LH fluxes during the cold surge were also higher than the average flux of winter monsoon.Due to the increase of SH flux and the decrease of solar radiation,the net heat budgets of the sea,during the cold surges before January,generally turned into high negative value,which caused the sea losing more heat than during winter monsoon,and even more than the average heat loss of the typhoons in 2008.At the end of winter monsoon,while the total solar radiation increased,the net heat budget of the sea turned to positive,so the SST increased gradually.Among all seasons,the SH flux in winter monsoon was the largest,the second largest in autumn,and the minimum in spring.The LH flux was the largest during summer monsoon,the second largest in winter,and the minimum occurred in autumn.