A Strong Internal Solitary Wave with Extreme Velocity Captured Northeast of Dong-Sha Atoll in the Northern South China Sea

Internal solitary waves (ISWs) in the South China Sea (SCS) have received considerable attention. This paper reports on a strong ISW captured northeast of Dong-Sha Atoll on 22 May 2011 by shipboard Acoustic Doppler Current Profiler (ADCP), which had the largest velocity among the ISWs so far reported in the global ocean. The peak westward velocity (u) was 2.94 m/s, and the peak downward velocity (w) was 0.63 m/s, indicating a first baroclinic mode depression wave. The amplitude of ISW inferred from ADCP backscatter was about 97 m. 2.2 h later, a trailing wave was captured with a peak westward velocity and downward velocity of 2.24 m/s and 0.42 m/s, respectively, surprisingly large for a trailing wave, suggesting that the ISW is type-A wave. The estimated baroclinic current induced by the leading ISW was much larger than the barotropic current. The Korteweg-De Vries (KdV) theoretical phase speed and the phase speed inferred from the satellite images were 1.76 m/s and 1.59 m/s, respectively. The peak horizontal velocity exceeded the phase speed, suggesting the ISW was close to or already in the process of breaking and may have formed a trapped core.

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Near 5-Day Nonisostatic Response to Atmospheric Surface Pressure and Coastal-Trapped Waves Observed in the Northern South China Sea

Journal of Physical Oceanography ◽

10.1175/jpo-d-17-0013.1 ◽

2017 ◽

Vol 47 (9) ◽

pp. 2291-2303 ◽

Cited By ~ 2

Author(s):

Ruixiang Zhao ◽

Xiao-Hua Zhu ◽

Jae-Hun Park

Keyword(s):

Hong Kong ◽

South China Sea ◽

South China ◽

Atmospheric Pressure ◽

Northern South China Sea ◽

Phase Speed ◽

Phase Lag ◽

Trapped Waves ◽

China Sea ◽

Coastal Trapped Waves

AbstractOceanic, nonisostatic responses to near 5-day Rossby–Haurwitz atmospheric pressure waves have been observed in open oceans; however, such responses based on observations in marginal seas such as the South China Sea have not been reported, owing to the limited ocean bottom pressure Pbot records. The Pbot measurements from pressure recording inverted echo sounders (PIESs) at sites in the northern South China Sea revealed a nonisostatic-like response near 5 days, although the coastal-trapped waves (CTWs) appeared to obscure it because their broadband periods include the near 5-day band. Cross-spectral analysis revealed that the PIES Pbot records and the sea level (SL) records of Hong Kong all correlate strongly with the atmospheric pressure and winds over the East China Sea. This is indicative of remotely forced CTWs. The PIES Pbot records showed higher coherence near 5 days with the zonal low-pass wavelength filters applied to the atmospheric pressure, and the phase analysis results strongly suggest nonisostatic oceanic responses to the westward-propagating Rossby–Haurwitz waves. Effective separation of CTWs and the nonisostatic responses from the Pbot records at the near 5-day period was achieved. The oceanic responses to the Rossby–Haurwitz waves in the northern South China Sea were nonisostatic; a 1-mbar change in air pressure resulted in a 1.58-mbar change in Pbot with a phase lag of 14.8°. The mean phase speed of CTWs from Hong Kong to station P3 was estimated to be 9.9 m s−1.

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The Relationship between POC Export Efficiency and Primary Production: Opposite on the Shelf and Basin of the Northern South China Sea

Sustainability ◽

10.3390/su10103634 ◽

2018 ◽

Vol 10 (10) ◽

pp. 3634 ◽

Cited By ~ 5

Author(s):

Teng Li ◽

Yan Bai ◽

Xianqiang He ◽

Xiaoyan Chen ◽

Chen-Tung Chen ◽

...

Keyword(s):

Organic Carbon ◽

South China Sea ◽

Primary Production ◽

South China ◽

Northern South China Sea ◽

Global Ocean ◽

China Sea ◽

Euphotic Layer ◽

Poc Export ◽

The Relationship

Accurate estimation of particulate organic carbon (POC) export efficiency in the euphotic layer is essential to understand the efficiency of the ocean’s biological carbon pump, but field measurements are difficult to conduct and data are sparse. In this study, we investigated the relationship between POC sinking export efficiency and ocean net primary production (NPP) in the euphotic layer of the northern South China Sea (NSCS), with the help of high spatiotemporal coverage satellite-derived NPP. Annual mean POC export efficiency in euphotic zone is 34% for the shelf areas and 24% for the basin of the NSCS in the context of satellite-derived 16-day-composited NPP. Similar to what is generally observed in the global ocean, the POC export efficiency on the shelf areas appears to be strengthened with the increase of NPP. However, in the basin areas, the opposite relationship is observed. That is, the POC export efficiency significantly decreases with the increase of NPP. Seasonal decoupling between NPP and POC export, phytoplankton size structure, grazing by zooplankton, and dissolved organic carbon export might account for the observed negative relationship between the POC export efficiency and NPP in the euphotic layer of basin region. System comparison between shelf and basin would be helpful to promote understanding of the regulation mechanism of POC export in the tropical marginal seas.

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Estimating Four-Dimensional Internal Wave Spectrum in the Northern South China Sea

Journal of Atmospheric and Oceanic Technology ◽

10.1175/jtech-d-18-0046.1 ◽

2019 ◽

Vol 36 (7) ◽

pp. 1199-1216

Author(s):

Hui Sun ◽

Wei Zhao ◽

Qingxuan Yang ◽

Shuqun Cai ◽

Xinfeng Liang ◽

...

Keyword(s):

South China Sea ◽

Internal Wave ◽

Internal Waves ◽

South China ◽

Large Scale ◽

Northern South China Sea ◽

Wave Spectrum ◽

Phase Speed ◽

Likelihood Method ◽

China Sea

AbstractInternal waves can transfer energy from large-scale to microscale processes; however, the spectra of these waves remain poorly known. A method that combines modal harmonic decomposition and maximum-likelihood method is proposed in this study to estimate four-dimensional internal wave spectrum using limited mooring observations. Using this method, a four-dimensional internal wave spectrum was obtained for the first time based on the mooring measurements collected during the South China Sea (SCS) Internal Wave Experiment in July 2014. The spectrum was then validated by comparing with the spectrum based on Fourier analysis and with the modified Garrett–Munk internal wave spectrum, respectively. The power of the internal wave spectrum decreased obviously with increasing frequency and wavenumber, with a falloff rate of ω−2 beyond tidal frequencies, and with falloff rates of and for horizontal and vertical wavenumbers, respectively. In addition, at a fixed frequency and vertical wavenumber, the propagation direction and phase speed of internal waves can be obtained through the four-dimensional spectrum. In summary, we verified the feasibility of estimating four-dimensional internal wave spectrum using limited mooring observations in this study, and the method we proposed should be applicable to other regions where such mooring observations are available.

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