The Effects of Latent Heating on Cold Frontal Speeds and Accelerations from a Potential Vorticity Perspective

Abstract

The effects of latent heating on frontal speed are investigated. It is conjectured that the existence of prefrontal latent heating leads to faster translation speeds and that the development of latent heating in the prefrontal zone can lead to frontal acceleration. A case study of a cold front where the attending precipitation band propagated into the prefrontal zone is presented. This front accelerated at the same time the precipitation moved into the prefrontal zone. Through inspection of the potential vorticity tendencies due only to latent heating, there is evidence that latent heating did alter the wind flow in the prefrontal zone, which may have contributed to positive frontogenetic tendencies in the prefrontal zone.

A sensitivity test was conducted comparing a control simulation of the case study to a simulation ignoring the effects of latent heating and evaporative cooling (a 'fake dry simulation') for the same event. The front in the fake dry simulation moved slower than the front in the control simulation. This is in agreement with the hypothesis that latent heating leads to faster frontal translation speeds. However, the individual contributions of latent heating and evaporative cooling could not be determined from this experiment. An additional simulation which included the effects of latent heating, but not evaporative cooling was performed. Although the intensity of the front was considerably reduced in this simulation, the speed of the front was nearly identical to that in the control simulation: suggesting that latent heating effects are more important in dictating frontal speed than evaporative cooling effects.