The Circulation Associated with a Cold Front. Part II: Moist Case

Abstract

The effect of moisture upon the dynamics of mature idealized cold front systems is investigated using a two-dimensional numerical model. Lifting produced by the initial cross-stream frontal circulation studied by Orlanski and Ross (1977) is shown to saturate the warm moist air above the nose of the front when initial humidity levels are sufficiently high. If the atmosphere is convectively unstable, this saturated air will develop into deep convection with the convection-induced circulation overwhelming the initial frontal circulation. The initial development of convection is also shown to produce a gravity wave exhibiting similar scales to those of the convective zone. This wave propagates into the warm air at a much faster speed than the moving front-cloud system. Comparisons are made of the intensity of convection for different initial humidity and temperature conditions and when a low-level capping inversion is present. Also a comparison is made of cloud development caused by a combination of frontal lifting and surface heating when temperature inversions of different intensifies are present. The stronger inversion is shown to suppress convection produced by surface heating alone with the combined effect of frontal lifting and surface heating required to release the convective instability.