On the energetics of the mean and eddy circulations in the lower stratosphere

Abstract

A hemispheric network of radiosonde stations is used in order to study the energetics of the lower stratosphere during the IGY period July 1957 through June 1958. For a hemispheric polar cap with 30 and 100 mb as top and bottom boundaries the balance equations of zonal and eddy kinetic energy, and zonal and eddy available potential energy are considered in detail. The eddies appear to build up the kinetic energy of the zonal flow at the expense of the eddy kinetic energy during all seasons. The eddies lose also eddy potential energy to the mean zonal distribution, in agreement with the abnormal upslope direction of the eddy heat transport. Thus, no source of energy for the eddy motions appears to be present in situ and the eddies must be forced by the circulation in the adjacent layers, probably by the tropospheric motions.The energy-cycle in the lower stratosphere is in many respects different from the one usually found in the troposphere, where, as is well known, eddy kinetic energy is destroyed by friction and the energy source is found in the creation of zonal available potential energy by radiation and the subsequent baroclinic processes. For the 100-30 mb layer the necessary kinetic energy is supplied by interaction at the top and/or bottom boundaries, while ultimately the energy is destroyed in the form of zonal available potential energy by radiation.