Current spectra under varying stratification conditions in the central North Sea |
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| Institution: | 1. Nanotechnology and Quantum Computing Lab., Shahid Beheshti University, G.C., Tehran, Iran;2. Department of Computer Engineering, Vali-e-Asr University of Rafsanjan, P.O. Box 518, Rafsanjan, Iran;3. Department of Electrical Engineering and Computer Science, University of California, Irvine, USA\n;1. College of Electronic Information and Optical Engineering, Nankai University, Tianjin, China.;2. Tianjin Key Laboratory of Optoelectronic Sensor and Sensing Network Technology, Nankai University, Tianjin, China.;3. School of Computer Science and Engineering, the University of Aizu, Aizu-Wakamatsu City, Fukushima 965-8580, Japan |
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| Abstract: | Given strongly different vertical stratification and not significantly different kinetic energy, ‘internal wave’ band spectral properties were studied using two 8-day representative sets of observations from the central North Sea in winter and summer. The observed similar spectral shape of the internal wave band was due to a combination of deterministic narrow band and intermittent signals. In addition to dominant tidal harmonics, 25% of total kinetic energy was found at inertial and non-linear inertial-tidal interaction frequencies in summer and about the same amount was found in broad-band response to atmospheric forcing in winter. The energy at the (seasonal) non-linear interaction frequencies was proportional to stratification, specifically, to near-inertial shear magnitude. In summer, motions at frequencies (σ) between f<σ<2.5 cpd (cycles per day) appeared in low vertical mode, whilst the power P(σ) of motions at σ>4±1 cpd obeyed canonical internal wave scaling P(σ)～Cσ?2, provided the shear magnitude ∣S∣ was used instead of the buoyancy frequency N for the factor C. Motions at 2.5<σ<4±1 cpd appeared as transition between the two regimes. In winter no inertial motions were observed. |
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