Influence of coastal effects, bottom topography, stratification, wind period, and mixing upon the propagation of internal waves and the profile of wind‐induced currents

Abstract

A three‐dimensional model in cross‐sectional form is used to examine the influence of wind period, stratification and bottom topography upon internal wave generation and wind‐induced current profiles in the coastal ocean. Calculations with fixed vertical diffusion coefficients and with a turbulence energy model are performed. These show that besides the wind period influencing the depth of penetration of the wind's momentum, as in a point model, it determines the offshore extent of internal waves generated at the coast. These waves together with elevation gradients modify the directly wind‐driven current profile found in a point model. For forcing at the subinertial frequency the internal wave field is trapped in the coastal region. Offshore the current can be derived from a point model incorporating wind forcing and an elevation gradient related to it. For wind forcing at the superinertial frequency the offshore extent of internal wave propagation increases with frequency. The local topography influences the offshore propagation of internal waves, leading at superinertial frequencies to regions of enhanced surface current magnitude in a similar manner to that found with internal tides. Calculations with the turbulence energy model show increased surface diffusion in these regions, which allows wind energy at both superinertial and subinertial frequencies to penetrate to depth in offshore areas. This process does not involve subinertial internal wave propagation. Conclusions are drawn as to the conditions under which a single point model can reproduce wind induced current profiles at an offshore location.