Upper-Ocean Temperature Response to Hurricane Felix as Measured by the Bermuda Testbed Mooring

Abstract

Hurricane Felix passed over the Bermuda testbed mooring on 15 August 1995, providing a unique opportunity to observe the response of the upper ocean to a hurricane. In the vicinity of Bermuda, Felix was a particularly large hurricane with hurricane-force winds over a diameter of about 300?400 km and tropical storm?force winds over a diameter of about 650?800 km. Felix moved northwestward at about 25 km h?1 with the eye passing about 65 km southwest of the mooring on 15 August. Peak winds reached about 135 km h?1 at the mooring. Complementary satellite sea surface temperature maps show that a swath of cooler water (by about 3.5°?4.0°C) was left in the wake of Felix with the mooring in the center of the wake. Prior to the passage of Felix, the mooring site was undergoing strong heating and stratification. However, this trend was dramatically interrupted by the passage of the hurricane. As Felix passed the mooring, large inertial currents (speeds of 100 cm s?1 at 25 m) were generated within the upper layer. The e-folding decay timescale of the inertial currents was about 9 days. The mixed layer depth was about 15 m before the arrival of Felix and deepened to about 45 m within three days after Felix?s passage; the temperature at 25 m decreased by approximately 3.5°?4.0°C. Large-amplitude temperature oscillations (?1.5°C) near the inertial period (inertial pumping effect) were set up by the hurricane in the seasonal thermocline resulting in vertical displacements of isotherms of approximately 15 m at 60?70 m. Comparative scale analyses of the upper-ocean responses to Hurricane Felix and Hurricane Gloria (1985) indicate that they have several similarities.