Steven M. Cavallo and Gregory J. Hakim
Department of Atmospheric Sciences, University of Washington,Seattle, WA
Monthly Weather Review, 138, submitted.
Tropopause polar vortices are coherent circulation features based on
the tropopause in polar regions. They are a common feature of the
Arctic, with typical radii less than 1500 km, and lifetimes that may
exceed one month. The Arctic is a particularly favorable region for
these features due to isolation from the horizontal wind shear
associated with the midlatitude jet stream, which may destroy the
vortical circulation. Intensification of cyclonic TPVs is examined
here using an Ertel potential vorticity framework to test the
hypothesis that there is an average tendency for diabatic effects to
intensify the vortices due to enhanced upper-tropospheric radiative
cooling within the vortices. Data for the analysis is derived from
numerical simulations of a large sample of observed cyclones over the
Canadian Arctic. Results show that there is on average a net tendency
to create potential vorticity in the vortex, and hence intensify
cyclones, and that the tendency is radiatively driven. While the
effects of latent heating are considerable, they are smaller in
magnitude, and all other diabatic processes have a negligible effect
on vortex intensity.