Horizontal Deflection of Acoustic Paths by Mesoscale Eddies

Abstract

The horizontal angular deflection of a ray path through a circular eddy is roughly 2v, where v is the fractional variation in sound speed at the eddy center; v may reach 0.03 for intense Gulf Stream rings but is typically < 0.01 for mesoscale eddies. A critical parameter is the ratio σ=vR/r of acoustic range R to the ?eddy focal length? r/v, where r is the eddy radius. Rays are split into horizontal multipaths for σ > 1. However, even for very intense rings at extreme ranges, we have σ < 1, and generally σ ? 1. Simple formulas are given for the horizontal deflection and for the perturbations in intensity and in travel time due to an eddy passing between source and receiver. Signatures of cold and warm core rings differ markedly because of differences in eddy dynamics, as well as differences in acoustic propagation properties. Fine-structure associated with internal waves induces a slight spread in the acoustic beam; the horizontal spread is of the same order as the horizontal deflection from mesoscale eddies.