Interaction of Potential Vorticity Anomalies in Extratropical Cyclogenesis. Part I: Static Piecewise Inversion

Abstract

The relative importance of various potential vorticity (PV) perturbations and their mutual interactions associated with the superstorm of 12–14 March 1993 are investigated by applying a piecewise PV inversion diagnostic system to a 36-h simulation of the storm. It is shown that the contributions from all PV anomalies to the surface development increase with time, although their relative significance varies during the rapid deepening stage. In general, the upper-level dry PV anomalies contribute the most to the rapid deepening of the storm, followed, in order, by the lower-level thermal anomaly and latent heat release. Comparing the PV anomalies and their inverted circulations reveals that there exists a favorable phase tilt between the upper- and lower-level anomalies that allows lower- and upper-level mutual interactions, in which the circulations associated with the upper-level PV anomalies enhance the lower-level anomalies and vice versa. In addition to the vertical interactions, lateral interactions are also present among the upper-level PV anomalies and the background flow. It is also found that the background flow advection dominates the vortex–vortex and vortex–background flow interactions in the deepening of the storm. The vortex–vortex interactions of the two upper-level positive PV anomalies cause the negative tilt of the main upper-level trough during the rapid deepening period.