On the movement and low-level structure of cold fronts

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. 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. -from Authors