The Potential Vorticity Structure of a Severe Extra-tropical Cyclone

Consideration is given to the dynamical structure of, and in particular the PV distribution within, extra-tropical cyclones that are accompanied by strong surface winds. The study entails a complementary combination of theoretical deductions based upon the PV-perspective of balanced flow and case-study examination of some extreme events of this kind.

The latter examination is in two parts. First diagnostic studies are undertaken using the routine ECMWF analysis fields, and second heuristic simulations of the same events are performed using a limited-area NWP model. Attention is devoted to the spatial distribution of the PV within the mature systems, the evaluation of the prior evolution of seminal components of the PV field.

It is shown that, despite strong case-to-case variability, there are some distinctive common features to the PV distribution of extra-tropical cyclones that spawn strong-winds.