The Wake of Hurricane Allen in the Western Gulf of Mexico

Abstract

In August 1980, Hurricane Allen passed over a moored array of instruments recording current, temperature and conductivity in the western Gulf of Mexico. An alongshore surge occurred during the storm passage, with the horizontal current speed reaching 91 cm s?1 in the thermocline (200 m) and diminishing to 15 cm s?1 32 m above the bottom (732 m). A wake of near-inertial frequency internal waves commenced after the storm passed the array. The alongshore current oscillation reached a maximum range of 50 cm s?1 within 3 days and decayed thereafter with a time scale of about 5 days. The current oscillations were clockwise-polarized and slightly elliptical, with a period of 22?23 h or about 85% of the local inertial period. Near-uniform upwelling of ±20 m occurred in the thermocline region (200?300 m) during the most intense part of the wake. Depth-leading phases of the horizontal current and temperature oscillations indicated downward radiation of wake energy. The wake oscillations were highly coherent over the vertical (500 m) and horizontal (100 km) scales of the array. The oscillations had a vertical scale much greater than the thermocline thickness (?150 m) and several times the ocean depth at the array site. Bemuse of the large vertical scale, downward radiation of wake kinetic energy was sufficient to account for the energy depletion rate in the thermocline, which suggests that dissipation was relatively unimportant during the early stage of wake decay.