Quasi-two-week And Synoptic Variability Of Upper Sea Temperature In The South China Sea (SCS)

The different time scale variations of sea temperature in the upper South China Sea (SCS) is determined from spectra analysis of one-year observational records which are observed from the three ATLAS (Autonomous Temperature Line Acquisition System) moorings buoys deployed in the central SCS during SCSMEX. Using harmonic analysis the upper sea temperature variations on annual, semi-annual cycle and on intraseasonal, quasi-two-week (10-20 day), synoptic (3-10 day) time scales are respectively obtained from the time series of sea temperature. When analyzing and discussing the quasi-two-week: variability and synoptic variability of see surface and subsurface temperature in the three stations of the SCS we give emphasis to the basic characteristics, forcing factors and the mechanism, and draw some important conclusions. In addition, the multi-scale variability of the upper sea temperature in the SCS is summarized based on the former studying work in this field. These studies make us know more about the upper thermal structure in the SCS. In this paper the following conclusions are mainly obtained.The quasi-two-week and synoptic signals of sea surface and subsurface temperature are found from the spectral analysis of the sea temperature data at the three stations, especially in subsurface layer at the station of SCS1, at which the quasi-two-week and synoptic variability is comparatively important and the analytical variance is about eight and three percent respectively. ?The quasi-two-week variability of upper sea temperature in the SCSIn this paper the quasi-two-week variability of sea surface and subsurface temperature in the SCS is found and studied and some new conclusions are obtained.In the SCS the upper sea temperature variability with a period of 10-20 day does exist, especially in winter and the amplitude is much larger at subsurface layer than at surface layer. The quasi-two-week variability of subsurface temperature is modulated by thermocline on seasonal cycle. When the thermocline deepens ( shoals) , the depth of the maximum amplitude of the subsurface quasi-two-week variability will increase (decrease) . At surface and subsurface layer the amplitudes are both larger in the north SCS than in the south SCS and the quasi-two-week variability is remarkably affected by monsoon in winter. There are four essential modes vertically, that is, subsurface temperature variability is in phase to, out of phase to, leads to or lags surface temperature variability.Low-level atmospheric forcing is the main reason of quasi-two-week variability of upper sea temperature. First, on the quasi-two-week time scales, variations of SST are mainly controlled by net surface heat flux. In winter latent heat flux and sensible heat flux are main, while in summer latent heat flux and net short wave radiations are main. SST can also be affected remarkably by subsurface temperature variability when wind-stress curl is strong. Second, variations of subsurface temperature result from vertical displacement of thermocline, which is primarily associated with variability of wind-stress curl and sometimes has something to do with wind-stress mixing and stratification in ocean.The formation of four vertical modes relates to the property of atmospheric forcing and to the background environment in atmosphere and ocean.? The synoptic variability of upper sea temperature in the SCSIn this paper the synoptic variability of upper sea temperature in the SCS is found and studied and the following main conclusions are obtained.The synoptic variability of upper sea temperature in the SCS does exist, especially at subsurface layer where amplitude is much larger than surface layer. On synoptic time scales, There is meridional difference of which upper sea temperature variability is stronger in north SCS than in south SCS and whose amplitude becomes weak from north to south. There is seasonal difference varying with stations. There are multiple modes vertically according to the sequence of variations of SST and subsurface temperature, that i...