Topographic modulation on the layered circulation in the South China Sea
<p>The South China Sea (SCS) is the largest semi-enclosed marginal sea in the western Pacific. It exhibits a unique vertically rotating cyclonic, anticyclonic, and cyclonic circulation in its upper, middle, and deep layers. Over slope topography, these layered currents interact and significant...
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| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2025-07-01
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| Series: | Ocean Science |
| Online Access: | https://os.copernicus.org/articles/21/1291/2025/os-21-1291-2025.pdf |
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| Summary: | <p>The South China Sea (SCS) is the largest semi-enclosed marginal sea in the western Pacific. It exhibits a unique vertically rotating cyclonic, anticyclonic, and cyclonic circulation in its upper, middle, and deep layers. Over slope topography, these layered currents interact and significantly shape the structure and intensity of the basin circulation. In this study, we employ process-oriented numerical simulations to investigate how upper-layer processes, characterized by greater magnitude and variability, influence the layered circulation over the irregular topographic slope. The simulations reveal that stronger upper intrusion from the open ocean directly enhances upper-layer circulation, which subsequently strengthens the middle and the deep slope currents. Vorticity dynamics illustrate that changes in the middle and deep slope current are largely related to the vertical stretching (<span class="inline-formula"><i>ζ</i><i>_</i>DIV</span>) induced by bottom geostrophic cross-isobath transport (<span class="inline-formula">CGT<sub>b</sub></span>). As the upper-layer cyclonic slope current intensifies, it modulates the bottom pressure distribution, resulting in stronger negative <span class="inline-formula"><i>ζ</i>_DIV</span> predominantly over the northwestern slope to intensify the middle anticyclone slope current. Similarly, for the deep cyclonic slope current, the <span class="inline-formula">CGT<sub>b</sub></span> maintains downwelling in the northern part and upwelling over the southern slope. Over the southern slope, the strengthening of the positive <span class="inline-formula">CGT<sub>b</sub></span> is induced by the increment of the advection of relative vorticity and planetary vorticity in the water column, in which the middle layer has an important contribution, but the upper layer has a minimal impact. Conversely, on the northern slope, the strengthening of the negative <span class="inline-formula">CGT<sub>b</sub></span> is primarily influenced by the upper layer.</p> |
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| ISSN: | 1812-0784 1812-0792 |