Observed Oceanic Response over the Upper Continental Slope and Outer Shelf during Hurricane Ivan

Abstract

Hurricane Ivan passed directly over an array of 14 acoustic Doppler current profilers deployed along the outer continental shelf and upper slope in the northeastern Gulf of Mexico. Currents in excess of 200 cm s?1 were generated during this hurricane. Shelf currents followed Ekman dynamics with overlapping surface and bottom layers during Ivan?s approach and transitioned to a dominant surface boundary layer as the wind stress peaked. Slope currents at the onset of Ivan were wind driven near the surface, but deeper in the water column they were dominated during and after the passage of Ivan by subinertial waves with a period of 2?5 days that had several characteristics of topographic Rossby waves. Currents on the slope at 50 m and greater depths commonly exceeded 50 cm s?1. Surprisingly, the strongest currents were present to the left of the storm track on the shelf while more energetic currents were to the right of the hurricane path on the slope during the forced stage. Near-inertial motion lasting for a time period of about 10 days was excited by the storm on the shelf and slope. Record wave heights were measured near the eyewall of Hurricane Ivan and were shown not to be rogue waves. The large surface waves and strong near-bottom currents caused significant bottom scour on the outer shelf at water depths as deep as 90 m.