A numerical study of wind-induced, near-inertial oscillations over the Texas-Louisiana shelf

The wind-induced, near-inertial oscillations over the Texas-Louisiana shelf were studied using a two-dimensional primitive equation model forced by an impulse of the surface wind. Numerical experiments reproduced the cross-shelf structure of observed near-inertial oscillations. For a given spatially uniform impulse of the wind, the model predicted the large near-inertial oscillations that were surface-intensified and characterized by a first baroclinic mode in the vertical. The oscillations reached a maximum kinetic energy near the shelf break and decayed gradually toward the coast but rapidly offshore. The magnitude and cross-shelf distribution of the wind-induced, near-inertial energy changed with wind direction. Effects of nonlinear advection on near-inertial oscillations were largest near the shelf break and decreased both onshore and offshore where the bottom topography was gentle or flat. They were stronger during the wind event and weaker after the wind ceased. Nonlinear interaction of tides and wind was weak on the shelf. However, it tended to provide a positive net contribution to near- inertial currents for both cases where tides were in and out of phase with winds. A simple theory suggests that the cross-shelf variation of near-inertial oscillations was controlled by the cross-shelf gradient of surface elevation and the vertical gradient of Reynolds stress.