On the influence of a surface coastal front on near-inertial wind-induced internal wave generation

Abstract

A numerical model is used to examine the wind-induced near-inertial internal waves in the coastal region in the presence of a surface front. Initial calculations with the front separating a well-mixed coastal region from a stratified offshore area in an infinite sea domain showed that away from the front, surface inertial oscillations are dominant. Near the front on the positive vorticity side, superinertial internal waves are generated and propagate offshore in an analogous manner to that found when stratification intersected a coastal boundary. However, in the case of a coastal boundary, the no-flow condition at the coast produced inertial oscillations at depth phase shifted by 180° from those at the surface. On the negative vorticity side of the front, internal waves at the subinertial frequency are trapped between the well-mixed region and the front. Some inertial energy is found at depth in the frontal region. Although the large-scale features of the distribution of inertial energy are independent of vertical eddy viscosity parameterization, its magnitude depends upon it. In the case of a stratified nearshore region and an offshore front, near-inertial waves generated at the coast were trapped between the coastal boundary and the front, which results in a surface region of enhanced inertial energy. This gradually decreased with time as inertial energy diffused to depth. This timescale depended upon vertical eddy viscosity magnitude. Copyright 2004 by the American Geophysical Union.