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Terrestrial Atmospheric and Oceanic Sciences








The variability of the upper water hydrographic structure, the efficacy of the different schemes for estimating the mixed layer depth (MLD), the inter-comparability estimation of the MLDs and diurnal and intra-annual MLD climatology in the tropical waters in the northern South China Sea were accessed in 702 depth-profiles of potential temperature (θ) and salinity collected in 64 cruises between 17.5 and 18.5°N and 115.3 and 116.3°E from 1997 to 2013. The hydrographic structure may be subdivided into three principal types: the classical type, with quasi-isopycnal surface mixed layer followed by an abrupt increase in the depth-gradient in θ and potential density (σθ) to mark the MLD; the stepwise type, with one or more small stepwise decreases in θ and/or increases in σθ in the mixed layer; and the graded type, with a general decrease in θ and increases in σθ with depth into the main pycnocline without a clear break to mark the MLD. These three types of upper waters were found in 75, 10, and 15% of the cruises. Out. of the 10 schemes for estimating the MLD, only the fixed temperature difference method of 0.5 and 0.8°C from the 10-m temperature yielded consistent results, with root mean square error and mean absolute percentage difference of 2 m and 2%. MLD varied diurnally with an average standard deviation of 4 m from the mean. The monthly average MLD reached a maximum of 80 m in December/January and dropped to a minimum of 25 m in May.


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Original Publication Citation

Jen-Hua, T., Wong, G. T. F., & Xiaoju, P. (2017). Upper water structure and mixed layer depth in tropical waters: The SEATS station in the northern South China Sea. Terrestrial, Atmospheric and Oceanic Sciences, 28(6), 1019-1032. doi:10.3319/TAO.2017.01.09.01


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