Trapping of the near-inertial wave wakes of two consecutive hurricanes in the Loop Current

Abstract

The near-inertial trapping of the wave wakes of two consecutive hurricanes at the base of the Loop Current is described using observations of a triangular mooring array. Hurricane Gustav translates over the Loop Current twice as fast and leads to a sharper, but equally strong, wind intensity peak than Hurricane Ike. Following the passage of Gustav, near-inertial oscillations in the main thermocline have large horizontal ((Formula presented.)) and vertical ((Formula presented.)) scales. The wave kinetic energy propagates down with a vertical group velocity of several tens of meters per day and leads to a downward energy flux of (Formula presented.). Observations suggest that the dispersion of the wave wakes produced by the hurricanes is driven by Doppler shifting in the upper (Formula presented.) and the vertical-varying vorticity inside the Loop Current. Near-inertial kinetic energy is enhanced and near-inertial oscillations are circularly polarized in a critical layer at the base of the Loop Current where the group velocity vector is nearly horizontal. The trapping and amplification of the near-inertial wave wakes of two consecutive hurricanes is addressed using a primitive equation numerical model. Numerical results suggest an increase of the near-inertial kinetic energy and vertical shear by a factor of (Formula presented.) near the critical layer due to wave-mean flow and wave-wave interactions. A K-profile parameterization of these interactions results in banded regions of elevated turbulent kinetic energy dissipation rates of (Formula presented.) for critical Richardson number Ric = 1, depending on the stratification of the water column.