The Heat Budget of a Midlatitude Squall Line and Implications for Potential Vorticity Production

Abstract

The water and heat budgets for a midlatitude squall line are estimated from single- and dual-Doppler-radar data and thermodynamic data from rawinsonde and thermodynamic retrieval (from dual-Doppler winds). These data, along with models to retrieve the freezing, melting, and radiative heating rates, yield vertical profiles of the heating within the convective, stratiform, and overhanging anvil areas of the squall line and differentiate the processes contributing to the total heating. The use of radar-derived vertical velocity information provides a more accurate delineation of the convective and stratiform components of the heating than can be obtained from rawinsonde data. The effects of diabatic heating on the potential vorticity (PV) field are calculated using a simple two-dimensional model and the vertical profiles of heating from the heat budget. The diabatic heating produced a deep column of high PV air coincident with the convective region and produced several regions of negative PV. Similar regions of negative PV were observed in the squall line. Upper-level negative PV within and to the rear of the stratiform precipitation region suggests that symmetric or inertial instability might favor intensification of the upper-level line-normal outflow there. Anticyclonic inertial turning of this outflow contributes to the formation of a strong upper-level jet in the line-parallel flow to the rear of the squall line.