Discretely Propagating Fronts

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9528853 Fritsch While the fundamental physics of fronts has been know for many years, new observational tools and theoretical frameworks are driving a reevaluation of some of the classical concepts. It has been observed over the years that frontal boundaries sometimes appear to propagate in a discrete rather than continuous manner. While observed with some frequency, this behavior has not been well documented nor studied in any depth. The principal investigator proposes to begin an exploratory study of discretely-propagating fronts. The objectives are: 1) establish the characteristics of discretely-propagating fronts and their environment, 2) determine why and how fronts propagate in a step-like (discrete) manner, 3) relate the processes of discrete propagation to current theories concerning frontogenesis, and 4) construct a conceptual model of discrete propagation. The research methodology is composed of four parts: 1) compilation of a ten year climatology of discrete propagation events using standard surface and upper air data, 2) compilation of the properties of individual events and construction of a composite environment, 3) numerical simulation of a representative event(s), and 4) calculation of the evolution of each of the terms (processes) that contribute to frontogenesis over the entire model domain and for the complete life cycle of the event(s). Under this initial research effort primary emphasis will be on objectives 1 and 2. While some progress is expected on the remaining objectives, they will be attacked more fully under a subsequent research effort that will be proposed only if warranted after completion of this exploratory effort. It is expected that the knowledge gained from these investigations will enhance our understanding of how frontogenesis is related to potential vorticity anomalies and, most importantly, why, and under what conditions, discrete propagation occurs. It is anticipate that the results will provide practica l benefits, such as improvements in short-term (3-18 h) weather forecasts. The results should also provide a basis for further theoretical studies of the frontogenesis problem. ***