EFFECTS OF MELTING ON FRONTOGENESIS

Frontal precipitation systems are simulated with a 2D cloud model incl uding ice-phase microphysics. Despite the use of idealized frontogenet ic forcing in the simulations, some observed characteristics of fronta l zones and their associated cloud and precipitation fields are reprod uced in the simulations. The effects of melting snow on surface fronto genesis is investigated. It is found that the cooling effects of melti ng snow significantly accelerate surface frontogenesis in winter storm environments, especially when the melting layer is close to the surfa ce. However, the steady-state surface frontal strength in the model is not sensitive to the melting effects. Finescale thermal and kinematic perturbations inside the frontal zone near the melting level, quite s imilar to those recently reported in the literature, are evident in th e model results. Analysis of the model results suggests that cooling f rom melting snow may induce these thermal and kinematic perturbations and may enhance baroclinicity, resulting in accelerating frontogenesis . These frontogenetic effects should be strongest when the melting lay er is near the surface, thus explaining the often observed coincidence of surface fronts with the surface rain-snow boundary in winter storm s.