Meso-βScale Potential Vorticity Anomalies and Rainbands. Part I: Adiabatic Dynamics of Potential Vorticity Anomalies

Abstract

The dynamics of mesoscale anomalies in the potential vorticity field is examined in a two-dimensional, semigeostrophic adiabatic frontogenesis model. Scale analyses and numerical simulations show that height- dependent anomalies can induce significant mesoscale structure in the circulation, which can be a mechanism for the formation of rainbands. It was found that broad and shallow shaped mesoscale anomalies (N2D2/f2L2 ? 1) induct more significant perturbations to the ageostrophic circulation than tall and narrow anomalies (N2D2/f2L2 ? 1). The time evolution of the anomalies is also studied and results show that in the midlevels the mesoscale perturbations on the frontal circulation generally decay with time. This is shown to be the direct consequence of the thermally direct circulations induced by the anomalies when forced by a deformation flow at the synoptic scale.