Potential Vorticity Anomalies Associated with Squall Lines

Abstract

Abstract This study involves observations and model simulations of potential vorticity anomalies in the wake of midlatitude squall lines. Using data from the Oklahoma–Kansas PRE-STORM experiment, we analyze potential vorticity fields near two squall lines—one with and one without a trailing stratiform region. From this observational analysis we suggest that squall lines with trailing stratiform regions can leave large, positive, midtropospheric potential vorticity anomalies in their wake. To further interpret these observations we consider a two-dimensional version of semigeostrophic theory formulated in isentropic and geostrophic coordinates, which results in a simple potential pseudodensity (inverse potential vorticity) equation. Using apparent heat source fields that model those computed diagnostically from PRE-STORM data, we find that theory does indeed predict large, midtropospheric potential vorticity anomalies for model squall lines with a trailing stratiform region but not for model squall lines t...