The Role of Diffusive Effects On Potential Vorticity In Fronts

Abstract

Theoretical studies of two‐dimensional fronts have shown that frictional processes at the time of occlusion and/or diabatic effects imply low‐level, positive potential vorticity (PV) anomalies. It is shown here that significant amounts of PV can be produced in an evolving baroclinic wave (taken to be the two‐dimensional semigeostrophic Eady wave) purely owing to the presence of a no‐slip, insulating lower boundary. A simple analytic expression is given for the time evolution of the mass‐weighted volume‐average PV, (PV), up to the point of frontal collapse. For the most unstable linear normal mode it is found, at the time of the formation of the frontal discontinuity, that the PV has increase..