The structure of an atmospheric warm front and its interaction with the boundary layer

Abstract

The detailed structure of a warm front has been determined from JASIN radiosonde data. The warm front was the base of a sloping moist layer over 200 km wide and 100 m barf deep, within which the baroclinicity was reversed and both observed and geostrophic wind backed with height. The maximum warm baroclinicity occurred at the top of this layer, well within the warm air. The resulting differential advection was such as to m aintain potential instability within the frontal zone. The warm air above the front exhibited a lam inar structure with two main bands of moist a ir; accelerations were significant in this region. Subsidence occurred in the cold air beneath the front, although the mean vertical motion became upward before the frontal passage. The decrease in depth of the cold air boundary layer was due to both subsidence and advection.