Observation of near-inertial internal waves on the continental slope in the northwestern South China Sea |
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| Authors: | Jie Zheng Jiwei Tian Hui Liang |
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| Institution: | 1.Physical Oceanography Laboratory,Ocean University of China,Qingdao,P. R. China |
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| Abstract: | Based on nearly 3 months of moored acoustic Doppler current profiler records on the continental slope in the northwestern South China Sea(SCS) in 2006,this study examines temporal and vertical characteristics of near-inertial internal waves(NIW).Rotary frequency spectrum indicates that motions in the near-inertial frequency are strongly polarized,with clockwise(CW) energy exceeding counterclockwise(CCW) by about a factor of 10.Wavelet analysis exhibits an energy peak exceeding the 95% confidence level at the frequency of local inertial during the passage of typhoon Xangsane(24 September to 4 October).This elevated near-inertial kinetic energy(NIKE) event possesses about a 4 days delay correlation with the time integral of energy flux induced by typhoon,indicating an energy source of wind.Further analysis shows that the upward phase velocity of this event is 3.8 m h~(-1)approximately,corresponding to a vertical wavelength of about 125 m if not taking the redshift of local inertial frequency into account.Rotary vertical wavenumber spectrum exhibits the dominance of clockwise-with-depth energy,indicating downward energy propagation and implying a surface energy source.Dynamical modes suggest that mode 1 plays a dominant role at the growth stage of NIW,whereas major contribution is from higher modes during the penetration of NIKE into the ocean interior. |
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