THE AVAILABLE POTENTIAL ENERGY BUDGET OF A SEVERE STORM-PRODUCING EXTRATROPICAL CYCLONE

SONG CHIN LIN, Purdue University

Abstract

Grid-scale and time mean flow available potential energy budget equations are derived. Computational analyses are carried out for both equations for a period (0000 GMT 3 April - 1200 GMT 4 April 1974) spanning the life cycle of a severe storm-producing extratropical cyclone which moved across the central United States. Among the diabatic heating components, total latent heat release and longwave radiation contribute significant positive and negative values, respectively, to the total diabatic heating. Total latent heat release is generally in good agreement with observed weather features and cyclone development. Grid-scale available potential energy budget results show that, during the development of the extratropical cyclone, the available potential energy within the region under investigation is increased. Diabatic generation is a source of available potential energy, but its value is rather small when compared with other budget terms. Available potential energy generation primarily results from the convective latent heat release ahead of the cold front in the warm sector. The diabatic heating fields in the cyclone vicinity and convection area contribute more effectively to increasing or maintaining the baroclinicity of the cyclone system than of the sub-regions themselves. There is a large amount of total potential energy release in the existing state of the atmosphere; however, only a small portion is converted into kinetic energy of the system. Horizontal transport of available potential energy is always a significant source of available potential energy. During the cyclone's development, a sizable amount of available potential energy is cascaded from grid to subgrid-scale motions. Available potential energy budget results for the time mean flow show that the available potential energy and its generation by diabatic processes are mainly attributed to the time mean flow regime. Vertical redistribution of the air by time mean vertical motion contributes to total potential energy release in the existing state and a gain in the reference state of the atmosphere. However, this same process by transient eddies contributes to total potential energy release in both states. In general, the time mean horizontal flow and horizontal transient eddies contribute equally to the inward available potential energy flux. The available potential energy associated with the time mean flow is supplied by transient waves.

Degree

Ph.D.

Subject Area

Atmosphere

COinS