The dynamics of coastal troughs and coastal fronts

Mesoscale structures in the wind and pressure fields are demonstrated by case studies. Two main types are identified. The one is characteristic for the coast of Northern Norway and is called coastal trough in this paper. The other, typical for the south-eastern coast, has similarities to the New England phenomenon named coastal front. Both occur during the winter season. The structures are quasi-permanent in certain weather conditions, which suggests a description in terms of a stationary model in two space dimensions, assuming that the variables do not change in a direction parallel to the straight coastline. The scaled equations depend on two non-dimensional numbers, which in general are small, permitting a series expansion of the perturbation variables. Solutions of zero and first order are derived, essentially by analytical methods. The size and structure of the solutions are compared to the case studies. The results seems to verify the initial hypothesis, namely that the trough is caused mainly by differential heating, while the front also depends on the discontinuity in surface friction.