Generation of Available Potential Energy of an Extratropical Cyclone System

Abstract

Generation of available potential energy of an extratropical cyclone system moving across the United States is computed for the period 20–21 March 1962 using standard rawinsonde data. A quasi-Lagrangian frame of reference is used and only the baroclinic component of generation, which is based on specification of a reference state and efficiency factors for the cyclone system, is considered. Parameterization schemes are used to estimate diabatic heating distributions due to convective and stable latent heat release and long-wave radiation. The heating fields are found to be in good agreement with observed weather patterns and computed kinematic parameters. Available potential energy generation estimates appear to be more representative than those from other similar studies of extratropical cyclones. Longwave radiation is a dominant source of available potential energy generation during the system's early development in the southwestern United States. Latent heat release rapidly becomes the major source of available potential energy generation as the system matures and is most important in the 700–500 mb layer. Stable (grid-scale) and convective (subgrid-scale) contributions are both significant. As the system begins to decay generation becomes extremely small.