Weather fronts in middle latitudes are represented as extended lines, seperating air masses with contrasting properties, on synoptic scale weather maps. A close-up view, however, shows the typical front as a transition zone, covering tens of kilometers in the cross-front direction, while extending for thousands of kilometers in the along-front direction. On the large scale, broad and converging wind patterns bring streams of contrasting air into collision at the frontal zone, tending to narrow and intensify it. Observations from instrumented towers and aircraft reveal a rich microsture within the zone, characterized by turbulence and large vertical motions. The small-scale processes act to mix properties, and to dissipate and disperse kinetic energy away from the zone, and thus tend to broaden and weaken the front. Blumen proposes to study the relative roles of these processes, acting on widely differing scales. Since there is, at present, no accepted conceptual model of the complex circulation within the zone, Blumen's approach is to postulate a simple (mathematically) set of dynamical models, representing both scales, varying in the values of a few coeffi- cients. Solutions will be sought that match the frontal zone to its ambient large scale flow regime. Such solutions provide predictions of key features of the zone, viz., energy dissipation rates, how energy is distributed among the smaller scales within the frontal zone, and the width of the zone. These predictions will be compared with observations collected during the STORM- FEST field experiment in 1992. The significance of this study is related to improvements in the quality of large-scale weather forecasting and climate simulation models. Currently available models do not take account of dissipation within frontal zones because the small scales are not resolved. The present approach is intended to provide some representation of this important process that could be used in future models.
