Absorption of Internal Waves by the Benthic Boundary Layer

Abstract

The interaction of near-inertial velocities with the benthic boundary layer above a flat bottom is investigated using a diagnostic model and a 3-month time series of velocity from a fixed array of current meters. The observed near-inertial motions are assumed to be due to internal waves and diurnal tides. If the vertical wavelength of the internal waves is much larger than the boundary-layer thickness, the turbulent stresses acting on the near-inertial motions and the work done by the stresses on these motions can be computed. The boundary layer is estimated to absorb ?0.003 to 0.024 erg cm?2 s?1 from the near-inertial motions, with one-third coming from the K1 diurnal tide and the rest from the internal-wave field. This is far less than estimated by Leaman (1976) and suggests that the benthic boundary layer on a flat bottom plays a minor role in dissipating internal-wave energy. This is also much less than the total energy dissipation in the boundary layer, suggesting that the boundary layer is primarily driven by low-frequency motions, not internal waves. A simple slab model with a linearized quadratic drag law qualitatively explains the observed near-inertial velocity structure and energy flux.