This paper focuses on the internal tide emitted from a continental slope in a uniformly stratified fluid. Results from numerical simulations using the MITgcm and from laboratory experiments performed on the Coriolis platform in Grenoble are compared. Due to their peculiar dispersion relation, internal gravity waves organize into localized beams of energy. We show that the beam structure is wellpredicted by the viscous theory of [10], assuming that the internal gravity wave field is emitted by a horizontally oscillating cylinder whose radius is the radius of curvature of the topography at the beam emission. The wave beam can bear a sub-harmonic parametric instability whose vertical scale is recovered from resonant interaction theory. Reflection of the wave beam on the bottom leads to the generation of harmonic beams, consisting of free and trapped waves.
We have designed a high-average-power diode-side-pumped Nd:YAG laser acousto-optically Q-switched at a pulse repetition rate range of 5-20 kHz. Double synchronized Q-switches were used for increasing the hold-off current and obtained more than 200 W average output power at 10 kHz and 110 ns pulse duration with more than 80% Q-switching efficiency and 20% optical-optical efficiency and instability of laser was 1%. The effects of various configurations of resonator on hold-off current of the laser have been experimentally studied.
Ocean processes can locally modify the upper ocean density structure, leading to an attenuation or a deflection of sound signals. Among these phenomena, eddies cause significant changes in acoustic properties of the ocean; this suggests a possible characterization of eddies via acoustics. Here, we investigate the propagation of sound signals in the Northeastern Atlantic Ocean in the presence of eddies of Mediterranean Water (Meddies). Relying on a high-resolution simulation of the Atlantic Ocean in which Meddies were identified and using the Bellhop acoustic model, we investigated the differences in sound propagation in the presence and absence of Meddies. Meddies create sound channels in which the signals travel with large acoustic energy. The transmission loss decreases to 80 or 90 dB; more signals reach the synthetic receivers. Outside of these channels, the sound signals are deflected from their normal paths. Using receivers at different locations, the acoustic impact of different Meddies, or of the same Meddy at different stages of its life, are characterized in terms of angular distributions of times of arrivals and of energy at reception. Determining the influence of Meddies on acoustic wave characteristics at reception is the first step to inverting the acoustic signals received and retrieving the Meddy hydrological characteristics.
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