Abstract
This paper presents a review of theoretical and observational studies relating to the low-level structure of cold fronts and explores the factors that are pertinent to frontal motion.
Observational studies have shown that, in some cases, surface cold fronts move at speeds faster than the normal component of the wind at all levels in the lower troposphere and therefore propagate. Other case studies have shown that the low-level flow immediately behind the front and normal to it is faster than the front and that the front has the local structure of a gravity current, its speed of movement being well determined by the gravity current speed equation. Them different types of behavior are related to results of recent theoretical studies, and the mechanism by which fronts can propagate is elucidated. It is shown that a necessary requirement for propagation is the existence of an alongfront temperature gradient.
We question the relevance of the gravity current speed equation in general, despite its apparent accuracy in some observed fronts, and note that it cannot be applied to the cold fronts simulated in simple frontogenesis models. The applicability of other simple frontal models providing estimates for the frontal speed is critically reviewed also.
