Passage of a tracer through frontal zones: A model for the formation of forward‐sloping cold fronts

Abstract It is shown that a forward‐sloping cold front may form in a simple two‐dimensional model of an atmospheric frontal zone, through differential advection of dry‐ and wet‐bulb potential temperature. As such, two frontal zones may coexist, with opposing slopes. This behaviour is manifest in the neutral Eady edge wave, which exhibits kata‐cold front behaviour, while the unstable Eady wave, with an ana‐cold front, does not generate a forward‐sloping cold front. These results come about as a consequence of the wave‐like behaviour of the fronts in the model, that is, the ability of a front to propagate through the air locally. As such, they highlight the fact that a frontal zone need not be a barrier to airflow and that any air properties, from water vapour to atmospheric pollution, may pass through a front.