Interpretations of the JEBAR Term

Abstract

In diagnostic calculations of the ocean's circulation, the so-called JEBAR (joint effect of baroclinicity and relief) term may induce a significant depth-average current field, as has been noted in the oceanographic literature. Here we present two consistent interpretations of this term. In the equation governing the vorticity of the depth-averaged current, a topographic vortex-stretching term proportional to the dot product of depth-averaged velocity and the depth gradient arises. We show that JEBAR corrects this term by removing the contribution of the geostrophic flow referenced to the bottom, which cannot generate topographic vortex stretching. In the evolution equation for the vorticity of the depth-integrated flow, a bottom-torque term is present. We show that the JFBAR term discussed above enters here as a contribution to the bottom torque, emphasizing the role of JEBAR as a forcing term. We also show that when a diagnostic calculation is formulated completely in terms of the transport stream-function, the procedure necessary to eliminate the bottom velocities in the friction term yields a frictional analogue of the JEBAR term.