Available Potential Energy and the Maintenance of the General Circulation

TLDR

Available potential energy is the excess atmospheric potential energy over its minimum possible value, typically about ten times the kinetic energy, and is conserved with kinetic energy under adiabatic flow but increases usually involve nonadiabatic processes. The study aims to characterize the general circulation by tracking the conversion of zonal available potential energy into eddy available potential energy, then into eddy kinetic energy, and finally into zonal kinetic energy. The authors partition available potential energy into zonal and eddy components via temperature‑variance analysis, then examine how zonal energy is converted to eddy energy through eddy heat transport and how each form is transformed into its kinetic counterpart.

Abstract

The available potential energy of the atmosphere may be defined as the difference between the total potential energy and the minimum total potential energy which could result from any adiabatic redistribution of mass. It vanishes if the density stratification is horizontal and statically stable everywhere, and is positive otherwise. It is measured approximately by a weighted vertical average of the horizontal variance of temperature. In magnitude it is generally about ten times the total kinetic energy, but less than one per cent of the total potential energy. Under adiabatic flow the sum of the available potential energy and the kinetic energy is conserved, but large increases in available potential energy are usually accompanied by increases in kinetic energy, and therefore involve nonadiabatic effects. Available potential energy may be partitioned into zonal and eddy energy by an analysis of variance of the temperature field. The zonal form may be converted into the eddy form by an eddy-transport of sensible heat toward colder latitudes, while each form may be converted into the corresponding form of kinetic energy. The general circulation is characterized by a conversion of zonal available potential energy, which is generated by low-latitude heating and high-latitude cooling, to eddy available potential energy, to eddy kinetic energy, to zonal kinetic energy.