On the polarization of oscillatory currents in the Bay of Biscay

Abstract

Rotary spectral properties were examined using ∼20 records of yearlong current observations in the Bay of Biscay. Here data are discussed from two representative records from 1000 m above the bottom at two sites, one above the continental slope and another above the abyssal plain. Nearly raw spectra revealed a strong prevalence for clockwise over anti‐clockwise circular motions at frequencies (σ) between ∼0.85f < σ < N (f and N denoting the local inertial and buoyancy frequencies, respectively). The observations showed rotary properties that were previously associated with free internal waves (for f < σ < N, N ≫ f), but only for motions in bands of ∼0.9 cpd width in frequency around inertial, tidal, and their nonlinear sum‐interaction frequencies. This width was larger than the enhanced kinetic energy bands of ∼0.15 cpd around inertial and tidal constituent frequencies. Nevertheless, it was suggested that both bands were associated with the same nonlinear interactions due to advection between subinertial and peak‐frequency motions that also resulted in internal wave intermittency.