Wind-induced internal wave dynamics near the Adriatic shelf break

Current and temperature measurements from a thermistor chain and current meter mooring were analysed to describe the near-surface internal wave field close to the middle Adriatic shelf break. Wind speed and direction from the nearby meteorological station Lastovo were analysed too, being a possible internal waves generating force. Spectral properties of currents and temperatures in the surface mixed and thermocline layers indicate strong deviations from the Garrett and Munk (Geophysical Fluid Dynamics 2 (1972) 225; Journal of Geophysical Research 80 (1975) 291) deep ocean internal wave models. The frequency spectra were dominated by three energetic bands: at 0.060 cph (near-inertial frequency), 0.080 cph (M2 tidal frequency) and between 3 and 4 cph. Near-inertial and high-frequency (3–4 cph) internal waves were generated by wind and/or surface wind waves. The frequency band 3–4 cph of high-frequency energetic waves does not correspond to the local Brunt–Väisälä frequency (30 cph), but to the thickest constant N layer below the thermocline—Sabinin (Izvestiya Academy of Sciences, USSR, Atmospheric and Oceanic Physics, English Edition 2 (1966) 872) “resonance layer”. Near-inertial oscillations represented a major contribution to the horizontal kinetic energy accounting for about 25% (10%) of the total surface (bottom) current variances. Vertically, the clockwise current vector rotations in the surface layer are out of phase by 180° compared with those below the thermocline. The level of surface near-inertial spectral peak was very high compared to the Garrett–Munk level, because of the proximity of wind generating force, while its bandwidth was typical for mid-latitudes.