Using 4.5 years of TOPEX/POSEIDON (T/P) altimetry data and 29 years of XBT data, we study the interannual and decadal variability in the South China Sea. In the 4.5-year T/P period, there exists strong quasi-biennial and quasi-penta-annual sea level height variability. Analysis of the 29-year XBT data indicates that the temperature field also has large quasi-biennial and quasi-penta-annual variability that is strongly modulated both interannually and decadally. The interannual variability is much stronger in the 80s than in the rest of the 29-year period. Modulation of the quasi-biennial and quasi-penta-annual variability in temperature suggests similar modulation might also exist for the interannual sea level height variability. In addition to the interannual variability there also exits strong decadal variability and a linear trend, which are stronger in the subsurface than near the surface. The XBT data indicates that below 100m, the South China Sea has been cooling (linear trend) at a rate of approx 0.4 deg per a decade, decreasing from the eastern basin to western basin. Similarly, decadal variability with a period of approx 18 years, in so much as the 29-year XBT data can reveal, also weakens from the eastern basin to the western basin. Differences between both the interannual and decadal variability within the South China Sea and in the Kuroshio (outside of the South China Sea) suggests that low-frequency variability in the South China Sea is mostly generated locally within the South China Sea.
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