Abstract
Using satellite altimetry sea surface height anomalies (SSHA) and Argo profiles, we investigated eddy’s statistical characteristics, 3-D structures, eddy-induced physical parameter changes, and heat/freshwater transports in the South China Sea (SCS). In total, 31,744 cyclonic eddies (CEs, snapshot) and 29,324 anticyclonic eddies (AEs) were detected in the SCS between 1 January 2005 and 31 December 2016. The composite analysis has uncovered that changes in physical parameters modulated by eddies are mainly confined to the upper 400 m. The maximum change of temperature (T), salinity (S) and potential density (σθ) within the composite CE reaches −1.5 °C at about 70 m, 0.1 psu at about 50 m, and 0.5 kg m−3 at about 60 m, respectively. In contrast, the maximum change of T, S and σθ in the composite AE reaches 1.6 °C (about 110 m), −0.1 psu (about 70 m), and −0.5 kg m−3 (about 90 m), respectively. The maximum swirl velocity within the composite CE and AE reaches 0.3 m s−1. The zonal freshwater transport induced by CEs and AEs is (373.6 ± 9.7)×103 m3 s−1 and (384.2 ± 10.8)×103 m3 s−1, respectively, contributing up to (8.5 ± 0.2)% and (8.7 ± 0.2)% of the annual mean transport through the Luzon Strait.
Highlights
The South China Sea (SCS) is the largest semi-closed marginal sea in the northwest Pacific
Considering that the research priority of this study is the oceanic eddy, we focus on the region (5◦ N–23◦ N, 108◦ E–121◦ E), and define this area as the SCS
The eddy-induced mixed layer depth (MLD) variation in the South China Sea (5.5 m for composite cyclonic eddy (CE) and 8.7 m for composite anticyclonic eddies (AEs)) is shallower than that in the Kuroshio Extension region (11.6 m for composite CE and 18.5 m for composite AE, Sun et al [40]) in terms of percentage change modulated by the composite eddy, there are no obvious differences between them (23.6% for composite CE and 38.4% for composite AE in Kuroshio Extension region)
Summary
The South China Sea (SCS) is the largest semi-closed marginal sea in the northwest Pacific. Based on the Simple Ocean Data Assimilation data and the Medium-Range Weather Forecasts altimeter data, Chen et al [28] studied the main features, inter-annual variability and the impact on local thermohaline structure of an eddy pair, i.e., a southern anticyclonic eddy (AE) and a northern CE off the eastern coast of Vietnam They found that the thermocline could be deepened by AEs, and shallowed by CEs. By combining in-situ measurements (five drifting buoys) with satellite observations, Nan et al [29] investigated three long-lived AEs near the 18◦ N section of the SCS in August 2007. The objective of this work was to reveal eddy’s surface characteristics, 3-D structures, eddy-induced changes of physical parameters and eddy-induced heat/freshwater transports in the SCS To achieve this goal, SSHA data and Argo profiles were applied in this study.
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