MESOSTRUCTURE OF DRY COLD FRONTS OVER FEATURELESS TERRAIN

Abstract

Serial pilot balloon flights, radiosonde and aircraft data in the vicinity of dry cold fronts and seabreeze fronts in summertime have made possible a clearer view of the meso-scale structure of such phenomena. In the velocity field, closed circulations and wave motions appear to be the rule, but the density variations associated with these features are inadequately known. Strong vertical currents frequently accompany the leading edges of these fronts. A tendency for increasing development of the vertical circulation with distance from the coast was found in the case of seabreeze fronts moving inland, strong circulations being found up to 135 mi from the coast. Cross-isentrope flow in the sections is deduced to indicate the effects of turbulent transfers, as well as frontal deformation. Frictional rather than geostrophic constraint is indicated for many fronts, especially those of the seabreeze variety. Strong circulations about the leading edge of the front are probably promoted by coastal effects and diurnal heating, deeper fronts being more productive of strong circulations than shallow ones. Evidence is presented for a connection between strong circulations of this type on the one hand, and frontal squalls, multiple structure and pressure jumps on the other.