Orateur
Description
Long-lived, self-lofting, diabatically-driven anticyclones co-located with aerosols and trace gases have been detected in the stratosphere following strong wildfire events. An important unresolved dynamical question is the apparent single-signed vorticity anomaly. The expected vorticity structure from localised heating is an anticyclone-above-cyclone dipole and recent idealised dynamical studies which incorporate an evolving heating tracer have indeed revealed this structure. Here, we demonstrate that a potential mechanism for the observed single-signed vortices is the action of background vertical shear. As expected from simple theory, when the vorticity anomalies are weak (small Rossby number) the vertical shear acts similarly on both anticyclone and cyclone. When the vorticity anomalies are strong (O(1) Rossby number), as is relevant to the observed cases, there is a range of shear magnitudes in which the cyclone is torn apart by the shear but the anticyclone survives.