Strong near-inertial oscillations in geostrophic shear in the northern South China Sea

Sun, Zhenyu; Hu, Jianyu; Zheng, Quanan; Li, Chunyan

doi:10.1007/s10872-011-0038-z

Cited by 50 publications

(40 citation statements)

References 17 publications

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“…Sanford, 1975;Leaman, 1975;Fu, 1981;van Haren, 2006), as observed in terms of an upward propagation of phase (e.g. Sun Z. et al, 2011). However, in this record the upward propagation of phase is not dominant.…”

Section: Vertical Propagation Of Phase and Energysupporting

confidence: 45%

“…However, the super-inertial energy is maximal near the surface, which is a commonly observed vertical structure for near-inertial motions (e.g. Shearman 2005;Zheng et al, 2006), whereas the sub-inertial energy is maximal at a deeper level of 15 m. Previous observations in this region only show a sub-inertial peak (Sun Z. et al, 2011). The mechanism for these two peaks will be discussed in Section 4.1.…”

Section: Primary Analysismentioning

confidence: 80%

“…The typhoon that frequently happens in summer can generate strong near-inertial motions, which can last for 1-2 weeks and have a current peak over 50 cm/s (e.g. Chen, 2006;Zhu and Li, 2007;Sun Z. et al, 2011). However, there is clear seasonal variability with the greatest near-inertial energy intensity in autumn (August, September and October, Chen et al, 2013).…”

Section: Introductionmentioning

confidence: 99%

“…Near-inertial energy is mostly baroclinic (Liang et al, 2005), and could induce turbulent mixing and chlorophyll-a enhancement (Zhang et al, 2014). The blue-shift (Sun L. et al, 2011) or red-shift (Sun Z. et al, 2011) of the local inertial frequency are observed and attributed to the background vorticity. Since the South China Sea spans a range of latitudes and dynamical regions, the character of near-inertial motions may vary throughout the South China Sea.…”

Section: Introductionmentioning

confidence: 99%

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Features of near-inertial motions observed on the northern South China Sea shelf during the passage of two typhoons

Chen

Polton

2015

Acta Oceanol. Sin.

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Abstract:Features of near-inertial motions on the shelf (60 m deep) of northern South China Sea were observed under the passage of two typhoons during the summer of 2009. There are two peaks in spectra at both sub-inertial and super-inertial frequencies.The super-inertial energy maximizes near the surface, while the sub-inertial energy maximizes at a deeper layer of 15 m. The sub-inertial shift of frequency is induced by the negative background vorticity. The super-inertial shift is probably attributed to the near-inertial wave propagating from higher latitudes. The near-inertial currents exhibit a two-layer pattern being separated at mid-depth (25~30 m), with the phase in the upper layer being nearly opposite to that in the lower layer. The vertical propagation of phase implies the near-inertial energy is not dominantly downward. The upward flux of near-inertial energy is more evident at the surface layer (<17 m). There exist two boundaries at 17 m and 40 m, where the near-inertial energy is reflected upward and downward. The near-inertial motion is intermittent and can reach a peak of as much as 30 cm/s. The passage of Typhoon Nangka generates an intensive near-inertial event, but Typhoon Linfa does not. This difference is attributed to the relative mooring locations, which is on the right hand side of Nangka's path (leading to a wind pattern rotating clockwise with time) and is on the left hand side of Linfa's path (leading to a wind pattern rotating anti-clockwise with time).

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Section: Vertical Propagation Of Phase and Energysupporting

confidence: 45%

Section: Primary Analysismentioning

confidence: 80%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Features of near-inertial motions observed on the northern South China Sea shelf during the passage of two typhoons

Chen

Polton

2015

Acta Oceanol. Sin.

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“…They are mainly generated by changing winds at the sea surface (Pollard and Millard, 1970;Chen et al, 2015b). The passage of a cyclone or a front can induce strong near-inertial motions (D'Asaro, 1985), which can last for 1-2 weeks and reach a maximum velocity magnitude of 0.5-1.0 m s −1 (Chen et al, 2015a;Zheng et al, 2006;Sun et al, 2011). In deep seas, the near-inertial internal wave propagates downwards to transfer energy to depth (Leaman and Sanford, 1975;Fu, 1981;Gill, 1984;Alford et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

A study on some basic features of inertial oscillations and near-inertial internal waves

Chen

Xing

2017

Ocean Sci.

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Abstract. Some basic features of inertial oscillations and near-inertial internal waves are investigated by simulating a two-dimensional (x − z) rectangular basin (300 km × 60 m) driven by a wind pulse. For the homogeneous case, nearinertial motions are pure inertial oscillations. The inertial oscillation shows typical opposite currents between the surface and lower layers, which is formed by the feedback between barotropic waves and inertial currents. For the stratified case, near-inertial internal waves are generated at land boundaries and propagate offshore with higher frequencies, which induce tilting of velocity contours in the thermocline. The inertial oscillation is uniform across the whole basin, except near the coastal boundaries (∼ 20 km), where it quickly declines to zero. This boundary effect is related to great enhancement of non-linear terms, especially the vertical non-linear term (w∂u/∂z). With the inclusion of near-inertial internal waves, the total near-inertial energy has a slight change, with the occurrence of a small peak at ∼ 50 km, which is similar to previous research. We conclude that, for this distribution of near-inertial energy, the boundary effect for inertial oscillations is primary, and the near-inertial internal wave plays a secondary role. Homogeneous cases with various water depths (50, 40, 30, and 20 m) are also simulated. It is found that near-inertial energy monotonously declines with decreasing water depth, because more energy of the initial wind-driven currents is transferred to seiches by barotropic waves. For the case of 20 m, the seiche energy even slightly exceeds the near-inertial energy. We suppose this is an important reason why near-inertial motions are weak and hardly observed in coastal regions.

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Observed upper ocean response to typhoon Megi (2010) in the Northern South China Sea

Guan

Zhao

Huthnance

et al. 2014

J. Geophys. Res. Oceans

131

117

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Typhoon Megi passed between two subsurface moorings in the northern South China Sea in October 2010 and the upper ocean thermal and dynamical response with strong internal tides present was examined in detail. The entire observed water column (60-360 m) was cooled due to strong Ekmanpumped upwelling (up to 50 m in the thermocline) by Megi, with maximum cooling of 4.2 C occurring in thermocline. A relatively weak (maximum amplitude of 0.4 m s 21 ) and quickly damped (e-folding time scale of 2 inertial periods) near-inertial oscillation (NIO) was observed in the mixed layer. Power spectrum and wavelet analyses both indicated an energy peak appearing at exactly the sum frequency fD1 (with maximum amplitude up to 0.2 m s 21 ) of NIO (f) and diurnal tide (D1), indicating enhanced nonlinear wave-wave interaction between f and D1 during and after typhoon. Numerical experiments suggested that energy transfer from NIO to fD1 via nonlinear interaction between f and D1 may have limited the growth and accelerated the damping of mixed layer NIO generated by Megi. The occurrence of fD1 had a high correlation with NIO; the vertical nonlinear momentum term, associated with the vertical shear of NIO and vertical velocity of D1 or vertical shear of D1 and vertical velocity of NIO, was more than 10 times larger than the horizontal terms and was responsible for forcing fD1. After Megi, surface-layer diurnal energy was enhanced by up to 100%, attributed to the combined effect of the increased surface-layer stratification and additional Megi-forced diurnal current.

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Strong near-inertial oscillations in geostrophic shear in the northern South China Sea

Cited by 50 publications

References 17 publications

Features of near-inertial motions observed on the northern South China Sea shelf during the passage of two typhoons

Features of near-inertial motions observed on the northern South China Sea shelf during the passage of two typhoons

A study on some basic features of inertial oscillations and near-inertial internal waves

Observed upper ocean response to typhoon Megi (2010) in the Northern South China Sea

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