An Investigation of the Influence of Latent Heat Release on Cold-Frontal Motion

Abstract

The effects of condensational heating on cold-frontal translation speed are explored through the use of potential vorticity (PV) diagnostics and model sensitivity experiments. It is hypothesized that condensational heating can lead to faster frontal translation speeds in the presence of vertical shear because of the horizontal propagation of the positive PV anomaly associated with the front. A case study of a cold front with an evolving precipitation structure is presented. A positive correlation existed between the position of condensational heating relative to the frontal zone and frontal translation speed, with faster frontal movement occurring when condensational heating was present in the prefrontal zone. This front was numerically simulated to see if the hypothesized mechanism for frontal movement was active. Through the use of a PV budget, it was confirmed that condensational heating did contribute to the forward propagation of the cold-frontal PV band. Numerical experiments were performed to establish the sensitivity of frontal speed to condensational heating, evaporative cooling, differential cloud cover, choice of cumulus parameterization, and choice of microphysical parameterization. The only simulation that exhibited a significant difference in frontal speed from that observed in the control simulation was the simulation in which the thermal effects of condensation were neglected. This result is consistent with the hypothesis that condensational heating in a sheared environment can serve to increase the forward translation speed of a cold front.