The Available Potential Energy of Storms

Abstract

The storm's available potential energy and its rate of change are derived for a vertically walled volume encircling the storm and extending from the surface to the top of the atmosphere. The rate of change includes explicit expressions for the generation of the storm's available potential energy, for its conversion to kinetic energy, and for its change through boundary work and energy flux. The theoretical results in isentropic coordinates show that it is not desirable to conduct available potential studies in a quasi-hydrostatic atmosphere for regions of limited vertical extent. The results also show the difficulty of inferring kinetic energy change from a total potential energy budget of a limited atmospheric domain. Opposite time rates of change for the storm's total and available potential energy are allowed through boundary processes for frictionless isentropic flows within mechanically open regimes. The relation of the available potential energy of storms to the available potential energy of the atmosphere is also established. Several recent diagnostic studies of the generation of the storm's available potential energy by individual diabatic components are summarized for the hurricane and extratropical cyclone. The amount of available potential energy generated within the storm is a significant fraction of the rate of its kinetic energy production.