By Paolo Franchi
High-frequency dynamics south-west of Svalbard. Poulain, Pierre-Marie ; Pennucci, Giuliana ; Lewis, Craig. CMRE-MR-2020-002. March 2021
This report deals with the environmental characterization of a strategic high-latitude area, the shelf break south-west of Svalbard, using data collected during the NARVAL19 sea trial in September-October 2019. The main focus is on high-frequency currents measured by four moored acoustic Doppler current profilers and 24 near-surface drifters for a period of about 10 days. Spectral and harmonic analyses were applied to the data and some results were compared to the currents predicted by a numerical barotropic tide model (Arc5km2018). The currents near the shelf break south-west of Svalbard are dominated by oscillatory motions at tidal frequencies, especially in the south-eastern part of the study area where they can reach 30-40 cm/s. Diurnal (K1) tidal currents are essentially barotropic in good qualitative agreement with the Arc5km2018 model. In contrast, semidiurnal (M2) currents have a baroclinic component with the amplitude and phase decreasing with depth. This corresponds to the upward phase propagation, which, for internal waves, is associated to downward propagation of energy. Both diurnal and semidiurnal signals appear to propagate northward with speeds near 20 and 12 km/h, respectively. The drifter tidal currents (at 15 m depth) are generally stronger than the depth-averaged tidal velocities estimated from the mooring ADCP data and the drifter tidal ellipses are more circular due to the possible contribution of inertial motion near the surface.