Abstract
Features of near-inertial motions on the shelf (60 m deep) of the 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 that the near-inertial energy is not dominantly downward. The upward flux of the near-inertial energy is more evident at the surface layer (<17 m). There exist two boundaries at 17 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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Foundation item: The National Natural Science Foundation of China under contract Nos 41276006, 40976013 and 41121091; the China Scholarship Council; the UK Natural Environment Research Council Programme FASTNEt under contract No. NE/I030259/1.
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Chen, S., Hu, J. & Polton, J.A. Features of near-inertial motions observed on the northern South China Sea shelf during the passage of two typhoons. Acta Oceanol. Sin. 34, 38–43 (2015). https://doi.org/10.1007/s13131-015-0594-y
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DOI: https://doi.org/10.1007/s13131-015-0594-y