Estimation of Horizontal Eddy Heat Flux in Upper Mixed-Layer in the South China Sea by Using Satellite Data

Yujuan Sun,Jiayi Pan

doi:10.1038/s41598-018-33803-2

Abstract

In this study, the horizontal eddy heat flux in the upper mixed-layer in the South China Sea (SCS) is derived from satellite-derived observational data of sea surface height anomalies and optimally interpolated sea surface temperature, as well as a reanalysis dataset of mixed-layer depth. The long-term heat flux shows a northward transport on the west side of the SCS, comparable with that in the Kuroshio extension with strong eddy activities. The eddy flux in the SCS has a prominent semi-annual cycle and becomes the strongest in winter and summer with the inflow flux in the south and the outflow in the northwest into the East China Sea through the Taiwan Strait. The semi-annual cycle is related to the strong semi-annul variabilities of the velocity and the temperature in areas southeast of Vietnam and in the northern SCS, respectively. In some areas of the SCS, the eddy heat flux can reach more than ~ 60% of the mean flow heat flux. The convergence of the eddy flux indicates that heat accumulates southeast of Vietnam, which may result in heat storage increases in the upper mixed-layer.

Highlights

The South China Sea (SCS) is a semi-enclosed marginal sea connecting the open Pacific mainly through the deep-water Luzon Strait to the east, and via a number of smaller and shallower passages in the Java Sea to the south
The eddy heat transport is calculated along the two sections shown in Fig. 1a, one located southeast of Vietnam and the other in the northern SCS, where the high fluxes are found
The horizontal eddy heat flux is calculated for the upper mixed-layer in the South China Sea based on the satellite observed sea surface height and temperature, as well as the reanalysis mixed-layer depth

Summary

Introduction

The South China Sea (SCS) is a semi-enclosed marginal sea connecting the open Pacific mainly through the deep-water Luzon Strait to the east, and via a number of smaller and shallower passages in the Java Sea to the south. It is found that the SCS upper layer heat structure can greatly affect the tracks and intensities of typhoons generated in and passing through the area. In this study, using satellite data of sea surface height and sea surface temperature, as well as mixed-layer depth reanalysis data, the eddy heat flux in the upper mixed-layer in the SCS is derived, and its seasonal variation is analyzed, along with heat flux convergence and divergence characteristics. Assuming the heat content (or storage) in the upper mixed-layer is of more significance to the air-sea exchange, we can estimate the eddy heat flux in the upper mixed-layer using: FQx = ρCpHT ′u′. Sea surface height anomaly data measured by satellite altimeters are used to calculate ∂h′/∂x and

Results

Discussion

Conclusion