Elliptical near-inertial surface currents and their decays under geostrophic and ageostrophic flows

Abstract

Elliptical near-inertial surface currents have been reported in the observations of coastal surface currents and satellite-tracked surface drifters, as well as the forward coastal circulation simulations forced with realistic driving forces and bottom bathymetry. The elliptical near-inertial surface currents are explained using a slab layer model formulated with horizontal shear and strain components, along with anisotropic constant frictional coefficients. The horizontal shear components, including background vorticity associated with geostrophic currents, contribute to the elliptical near-inertial currents with reduced eccentricity, and the horizontal strain components related to geostrophic currents (e.g., vertical currents due to direct wind-driven upwelling and down-welling and indirect wind stress curl-driven Ekman pumping, and frontal-scale vertical circulation) lead to the modification of the temporal decay time scales of the near-inertial surface currents.