The Influence of Horizontal Inhomogeneities on the Propagation of High-Frequency Linear Internal Gravity Waves across a Baroclinic Flow

Abstract

The effect of the inclusion of the horizontal gradients of background density and baroclinic flow on the propagation of linear internal gravity wave packets across the flow is investigated using ray-tracing techniques. The focus is on the behavior of wave packets at the boundaries of regions supporting wave propagation as well as on identifying the locations of critical layers. For the case of isopycnals with constant slope but arbitrary spacing, it is shown that the critical-layer valves (critical layers for which one wave may pass through while another encounters a critical layer) found if the horizontal gradients are not included do not exist. An analytic example of a quite different basic state that has a critical-layer valve is presented. It has the property that for the wave encountering a critical layer, the group velocity goes to infinity as it is approached and the wavenumber also goes to infinity. The analytic and numerical results indicate that critical layers occur in only a few special cases. One case where they do occur is an important one; namely, that of high-frequency waves in a tidally mixed front.