Observed Oceanic Surface Modes in the Northern South China Sea

Quan，Qi1; Liu，Zhiqiang2; Xue，Huijie3; Hu，Jianyu3; Wang，Qiang4; Zhang，Han5,6; Liu，Xiaohui5; Jin，Guangzhen7; Wang，Ya Ping1

2023-08-01

10.1175/JPO-D-22-0250.1

Journal of Physical Oceanography   Impact Factor & Quartile

0022-3670

1520-0485

Using observations and theoretical models, a substantial topographic modulation on the quasigeostrophic (QG) dynamics, which results in a primary surface mode distinct from the classic first baroclinic (BC1) mode with a flat bottom, is revealed in the northern South China Sea (NSCS). In contrast to open oceans, the surface-intensified modes decay downward more rapidly over the continental slope of the NSCS, with a mean e-folding scale of approximately 1/5 of water depth. The subinertial flow variability appears to be vertically incoherent, with planetary and topographic Rossby waves dominating in the upper and deep layers, respectively. With a larger deformation radius (R), the surface-mode Rossby waves propagate at a phase speed ∼1.5 times of that of the BC1 mode. Moreover, the modal structures can be substantially modified by seasonal NSCS circulation, which is significantly enhanced over continental slopes. Analysis of the triad interactions further implies that the short waves tend to transfer energy to larger scales via the inverse cascade and only those with wavelengths larger than R ≈ 70 km in the NSCS can persist because of a slower unstable growth rate but a higher fraction of upscale energy transfer. The present theory excludes the bottom-trapped mode, which is closely associated with topographic Rossby waves and is observed to be significant in the abyssal NSCS. Hence, a complete normal-mode basis for any QG state is required for a study that focuses on flow variability throughout the water column. Our findings provide an insight into the vertical partition of horizontal kinetic energy for QG motions, as well as the relevant oceanic varia-tion in marginal seas.

Baroclinic flows Instability Quasigeostrophic models

SCI

English

Corresponding

National Natural Science Foundation of China[42006007];National Natural Science Foundation of China[42276004];National Natural Science Foundation of China[91958203];

Oceanography

Oceanography

WOS:001045987300002

AMER METEOROLOGICAL SOC

GEOSCIENCES

2-s2.0-85168156452

Scopus

1.State Key Laboratory of Estuarine and Coastal Research,East China Normal University,Shanghai,China
2.Department of Ocean Science and Engineering,Southern University of Science and Technology,Shenzhen,China
3.State Key Laboratory of Marine Environmental Science,and Department of Physical Oceanography,College of Ocean and Earth Sciences,Xiamen University,Xiamen,China
4.State Key Laboratory of Tropical Oceanography,South China Sea Institute of Oceanology,Chinese Academy of Sciences,Guangzhou,China
5.State Key Laboratory of Satellite Ocean Environment Dynamics,Second Institute of Oceanography,Ministry of Natural Resources,Hangzhou,China
6.Shanghai Typhoon Institute,China Meteorological Administration,Shanghai,China
7.Rosen Center for Advanced Computing,Purdue University,West Lafayette,United States

Quan，Qi,Liu，Zhiqiang,Xue，Huijie,et al. Observed Oceanic Surface Modes in the Northern South China Sea[J]. Journal of Physical Oceanography,2023,53(8):1835-1849.

Quan，Qi.,Liu，Zhiqiang.,Xue，Huijie.,Hu，Jianyu.,Wang，Qiang.,...&Wang，Ya Ping.(2023).Observed Oceanic Surface Modes in the Northern South China Sea.Journal of Physical Oceanography,53(8),1835-1849.

Quan，Qi,et al."Observed Oceanic Surface Modes in the Northern South China Sea".Journal of Physical Oceanography 53.8(2023):1835-1849.