Observed and Simulated Energy Cycles in the Frequency Domain

Abstract

The analysis of spectral energetics in the frequency domain has been applied to several observed datasets and those simulated by a GFDL general circulation model. There exists good agreement on the directions of energy flows between the observed and the simulated atmospheres. The conversion from available potential energy to kinetic energy in the tropics and extratropics is the major source of eddy kinetic energy for all the low and high frequency bands discussed. The energy balance in the tropics has quite different characteristics from those in the extratropics. Instead of an up-scale decascade as in the case of the extratropics, kinetic energy is transferred in an opposite sense, namely from transients of longer time scales to those of shorter time scales. Using a 5-year dataset from the ECMWF operational analysis, an energy cycle is obtained that is in general agreement with the one computed using the data of the FGGE year alone. The interannual variability of the spectral estimates is relatively small compared with the discrepancies caused by the variety of data origins.