Dynamical analysis of submesoscale fronts associated with wind-forced offshore jet in the western South China Sea

Xiaolong Huang; Zhiyou Jing; Ruixi Zheng; Haijin Cao

doi:10.1007/s13131-020-1671-4

Volume 39 Issue 11

Dec. 2020

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Xiaolong Huang, Zhiyou Jing, Ruixi Zheng, Haijin Cao. Dynamical analysis of submesoscale fronts associated with wind-forced offshore jet in the western South China Sea[J]. Acta Oceanologica Sinica, 2020, 39(11): 1-12. doi: 10.1007/s13131-020-1671-4

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Xiaolong Huang, Zhiyou Jing, Ruixi Zheng, Haijin Cao. Dynamical analysis of submesoscale fronts associated with wind-forced offshore jet in the western South China Sea[J]. Acta Oceanologica Sinica, 2020, 39(11): 1-12. doi: 10.1007/s13131-020-1671-4

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Dynamical analysis of submesoscale fronts associated with wind-forced offshore jet in the western South China Sea

doi: 10.1007/s13131-020-1671-4

Xiaolong Huang^{1, 2},
Zhiyou Jing^{1, 3, 4
,
,},
Ruixi Zheng^{1, 2},
Haijin Cao⁵

1.
State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China
2.
University of Chinese Academy of Sciences, Beijing 100049, China
3.
Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou), Guangzhou 511458, China
4.
Innovation Academy of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences, Guangzhou 510301, China
5.
College of Oceanography, Hohai University, Nanjing 210024, China

Funds: This work is supported by the Chinese Academy of Sciences under contract Nos ZDBS-LY-DQC011, ZDRW-XH-2019-2 and ISEE2018PY05; the Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) under contract No. GML2019ZD0303; the National Natural Science Foundation of China under contract Nos 41776040 and 92058201; the Pilot National Laboratory for Marine Science and Technology (Qingdao) under contract No. OCFL-201804; the State Key Laboratory of Tropical Oceanography under contract No. LTO1907; the Guangzhou Science and Technology Project under contract No. 201904010420.

More Information

Corresponding author: E-mail: jingzhiyou@scsio.ac.cn
Received Date: 2020-04-13
Accepted Date: 2020-07-08

Available Online: 2020-12-28

Publish Date: 2020-11-25

Abstract

Abstract

This study investigates the submesoscale fronts and their dynamic effects on the mean flow due to frontal instabilities in the wind-driven summer offshore jet of the western South China Sea (WSCS), using satellite observations, a 500 m-resolution numerical simulation, and diagnostic analysis. Both satellite measurements and simulation results show that the submesoscale fronts occupying a typical lateral scale of O(~10) km are characterized with one order of Rossby (Ro) and Richardson (Ri) numbers in the WSCS. This result implies that both geostrophic and ageostrophic motions feature in these submesoscale fronts. The diagnostic results indicate that a net cross-frontal Ekman transport driven by down-front wind forcing effectively advects cold water over warm water. By this way, the weakened local stratification and strong lateral buoyancy gradients are conducive to a negative Ertel potential vorticity (PV) and triggering frontal symmetric instability (SI) at the submesoscale density front. The cross-front ageostrophic secondary circulation caused by frontal instabilities is found to drive an enhanced vertical velocity reaching O(100) m/d. Additionally, the estimate of the down-front wind forcing the Ekman buoyancy flux (EBF) is found to be scaled with the geostrophic shear production (GSP) and buoyancy flux (BFLUX), which are the two primary energy sources for submesoscale turbulence. The large values of GSP and BFLUX at the fronts suggest an efficient downscale energy transfer from larger-scale geostrophic flows to the submesoscale turbulence owing to down-front wind forcing and frontal instabilities. In this content, submesoscale fronts and their instabilities substantially enhance the local vertical exchanges and geostrophic energy cascade towards smaller-scale. These active submesoscale processes associated density fronts and filaments likely provide new physical interpretations for the filamentary high chlorophyll concentration and frontal downscale energy transfer in the WSCS.
- submesoscale fronts,
- enhanced vertical velocity,
- energy transfer,
- offshore jet,
- western South China Sea

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References(69)

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