Near‐inertial oscillations over the Texas‐Louisiana shelf

Abstract

Wind‐induced, near‐inertial oscillations over the Texas‐Louisiana shelf in spring and summer 1992 are described using the current and wind observations taken during the first year of the Texas‐Louisiana Shelf Circulation and Transport Processes Study (LATEX A). Rotary spectral analysis shows clockwise‐rotating energy peaks at near‐inertial frequencies for records from all current meter moorings after the suppression of principal tidal signals. The vertical structure of near‐inertial oscillations is characterized by a first baroclinic mode with a near 180° phase difference between the upper mixed layer and the lower stratified layer. The oscillations are intermittent with a modulation timescale of about 5–10 days. They are surface‐intensified and have maximum values near the shelf break, decaying gradually toward the coast but rapidly offshore. Near‐inertial oscillations appear to accompany a sudden change of the wind stress during frontal passages. Diagnostic analysis suggests that the large near‐inertial oscillations over the LATEX shelf are mainly generated by high‐frequency (near‐inertial) variation of the wind stress accompanying the passage of atmospheric fronts. When the downward transfer of the near‐inertial energy to the deep stratified layer is small, a simple mixed layer model forced by the observed wind stress provides a reasonable prediction of the near‐inertial currents in the mixed layer.