Idealized shallow-water simulations of potential vorticity perturbations in zonal jet-waveguides and links to observed dynamical processes

This study investigates the propagation of negative potential vorticity (PV) anomalies in idealized shallow-water simulations, with particular emphasis on how their evolution is governed by the structure and latitude of the jet. The initial conditions of the experiments constitute a zonally symmetric midlatitude jet representing a Rossby waveguide, and an isolated, axisymmetric negative PV vortex representing upper-level ridges and diabatically generated outflows associated with warm conveyor belts (WCBs).

The experiments provide a first systematic demonstration that vortex propagation is governed by the combined effects of intrinsic Rossby-wave propagation and advection by the jet, with the relative importance of these processes determined by the latitude of vortex initialization relative to the jet. Importantly, the resulting propagation behavior is not symmetric about the position of the vortex relative to the jet axis. 

These results also provide a direct dynamical analogue for the behavior of WCB outflows across different interaction types with the Rossby waveguide in the real atmosphere. In particular, vortices initiated close to the jet core or slightly equatorward correspond to no-interaction WCB outflows, which exhibit rapid advection and equatorward displacement. The ridge-interaction outflows, characterized by relatively weaker advection, are represented by vortices initialized on the poleward flank of the jet. In contrast, anomalies initialized farther poleward of the jet, with minimal direct influence from the westerlies and quasi-stationary behavior, correspond to blocking and cutoff interactions of WCB outflows.

The structure of the jet is equally important: variations in jet strength in the idealized simulations modulate the degree of eastward advection of the vortices, while changes in jet width and latitude primarily shift the spatial extent of the jet’s influence; in all cases, vortex behavior is governed by its relative position with respect to the Rossby waveguide.