NEAR-INERTIAL PROPAGATION INSIDE MESOSCALE EDDIES

The present study was motivated by observations of intense near-inertial wave activity above and below the core of the semi-permanent anticyclonic Cyprus eddy in the Eastern Mediterranean during the BOUM field campaign.

To explain the observations, we have conducted a general numerical study of eddy/near-inertial interactions with a Boussinesq (nonhydrostatic) model. The problem is posed as an initial-value problem, with initial conditions consisting of an isolated shielded vortex in geostrophic equilibrium and surface-intensified near-inertial oscillations designed to simulate a uniform wind impulse. When ambient parameters (eddy strength and extent, mean stratification profile) are matched to the BOUM observations, our numerical results replicate quite well the wavelengths and intensity of the observed near-inertial wave field inside and below the Cyprus eddy core. The nature of near-inertial wave propagation inside an eddy is further explored as a function of initial near-inertial amplitudes at the surface and ambient stratification. Downward near-inertial propagation is most pronounced in the center of the eddy where the vortex velocity is zero (anticyclonic vorticity a maximum), and can be explained by means of a simple theoretical formulation based on transmission coefficients in a piecewise-linear approximation to the density profile. Extension to propagation within a field of several eddies is also discussed.