Previous studies have approached lee wake formation largely in terms of the production of vertical vorticity and/or potential vorticity (PV) in the wake. However, it has remained uncertain how much information these two approaches actually provide about the dynamics of wake formation. Indeed, a formal scaling analysis of the equations of motion in vorticity-vector potential form shows that for predominately hydrostatic nonrotating flows, the vertical vorticity does not induce any velocity--that is, hydrostatic nonrotating flow is completely determined by the horizontal vorticity. Similarly, it does not appear possible to determine the flow field from knowledge of PV in this limit. Such considerations suggest that the appropriate starting point for an analysis of lee wake formation is consideration of the horizontal vorticity structures present in the flow.

Here we consider kinematic inversions of idealized horizontal vorticity distributions in an effort to identify the characteristic vortex structures associated with lee wake formation. It is shown that these idealized vorticity distributions predict a number of flow features associated with lee wakes, including reversal of the surface flow downstream of the obstacle, lee-side surface front formation, and ultimately the production of circulation about a vertical axis. The idealized calculations are then compared to stratified numerical simulations in an effort to demonstrate the formation of such vorticity structures and their evolution in time. Finally, identification of these characteristic structures allows us to predict wake formation in a number of contexts not previously considered, such as flow into a basin and flow past a heat source on a sloped boundary.