A comparative study on Omega equation-based vertical velocity diagnosis for the South China Sea

Hong Kunqiang; Xie Lingling; Huang Jiahui

doi:10.12284/hyxb20250109

Volume 47 Issue 12

Dec. 2025

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Hong Kunqiang，Xie Lingling，Huang Jiahui. A comparative study on Omega equation-based vertical velocity diagnosis for the South China Sea[J]. Haiyang Xuebao，2025, 47(12)：10–24 doi: 10.12284/hyxb20250109

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A comparative study on Omega equation-based vertical velocity diagnosis for the South China Sea

doi: 10.12284/hyxb20250109

Hong Kunqiang^1
,,
Xie Lingling^{1, 2, 3},
Huang Jiahui^{1, 4
,
,}

1.
Laboratory of Coastal Ocean Variation and Disaster Prediction, College of Oceanology and Meteorology, Guangdong Ocean University, Zhanjiang 524088, China
2.
Guangdong Key Laboratory of Climate, Resource and Environment in Continental Shelf Sea and Deep Ocean, Zhanjiang 524088, China
3.
Guangdong Western Tropical Marine Ecological and Environmental Field Observation Research Station, Zhanjiang 524088, China
4.
Zhanjiang Marine Center, Ministry of Natural Resources, Zhanjiang 524005, China

Received Date: 2025-07-11
Rev Recd Date: 2025-11-05

Available Online: 2025-12-04

Publish Date: 2025-12-31

Abstract

Abstract

Based on 0.1° × 0.1° high-resolution temperature, salinity, and three-dimensional velocity data from the Ocean general circulation model For the Earth Simulator (OFES), this study analyzes the applicability of the Omega equation for diagnosing vertical velocity in the South China Sea (SCS) and the spatiotemporal variation characteristics of vertical velocity in the SCS. The results show that the vertical velocity diagnosed by the Omega equation (w_Omega) and the OFES model vertical velocity (w_OFES) are of comparable magnitude in most areas of the SCS basin, approximately O(10⁻⁵ m/s), while w_Omega is one order of magnitude smaller than w_OFES on the northern continental shelf of the SCS. The spatial correlation coefficient (r^s) between w_Omega and w_OFES is larger in the region southwestern of Taiwan (R1) and east of Vietnam (R2), and smaller in the western Philippines (R3), the southern SCS (R4), and the northeastern region of Hainan Island (R5). In terms of seasonal variation, r^s is larger in winter and smaller in summer in regions R1, R2, and R4, while regions R3 and R5 show no significant seasonal characteristics in r^s. Regions R1 and R2 are applicable areas for the Omega equation, where the temporal correlation coefficient r^t between w_Omega and w_OFES is larger. In all regions, the contribution of the deformation term ($ {S}_{{\mathrm{DEF}}} $) exceeds 50%, generally greater than the contribution of the advection term ($ {S}_{{\mathrm{ADV}}} $), and they exhibit a common vertical structure of “$ {S}_{{\mathrm{ADV}}} $ dominance in the upper layer and $ {S}_{{\mathrm{DEF}}} $ enhancement in the lower layer”, with the critical depth ranging from 20−70 m. Comparing the results of vertical velocity diagnosed by effective Surface Quasi-Geostrophy (eSQG) and the Omega equation, the Omega equation is significantly better adapted for diagnosing vertical velocity in the SCS.
- South China Sea,
- vertical velocity,
- Omega equation,
- OFES,
- spatio-temporal variation,
- eSQG

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References(58)

References

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