Horizontal potential vorticity dipoles on the convective storm scale

Abstract

AbstractThe structure and dynamics of potential vorticity (PV) anomalies generated by convective storms is investigated both theoretically and in a numerical model case study. Linear theory suggests that if the storm‐induced heating is on a sufficiently small scale (relative to the Rossby radius of deformation), and the environment contains moderate vertical wind shear (of order 1 m s−1 km−1), then the dominant mode of a diabatically generated PV anomaly is a horizontally oriented dipole. The horizontal dipoles are typically of 𝒪(10 PVU), compared with the 𝒪(1 PVU) vertical dipoles that have been studied extensively throughout the literature. Furthermore, the horizontal PV dipoles are realized almost entirely as relative vorticity anomalies (on a time‐scale of the order of tens of minutes after the heating has been turned on). The analysis of horizontal PV dipoles offers a new perspective on the vorticity dynamics of individual convective cells, implying that moist processes play a role in the maintenance of vertical vorticity in the convective storm environment. Copyright © 2009 Royal Meteorological Society