Estimation of Atmospheric Energetics in the Frequency Domain during the FGGE Year

Abstract

The energetics of atmospheric motions are studied in the frequency domain using the two versions of the FGGE IIIb dataset, processed at GFDL and ECMWF. It is demonstrated that the frequency spectra of kinetic energy (KE) and available potential energy (APE) can be approximated by a power law. On a log?log diagram, a slope of minus one results for both KE and APE in the period range of 7 to 35 days, when integrated over the Northern Hemisphere. The conversion from APE to KE is the major source of eddy kinetic energy for all the low and high frequency bands discussed. Through nonlinear interactions, motions of high frequencies (with periods shorter than 10 days) gain APE from, and lose KE to the motions of low frequencies (with periods longer than 10 days but shorter than the annual cycle). The nonlinear energy exchanges are relatively more important for the energy balance of low frequency modes. It is also shown that both high and low frequency transients extract APE from and supply KE to the time-mean flow. The intercomparisons between the two versions of FGGE data indicate an overall agreement between the energy cycles derived from the GFDL and ECMWF datasets, despite the differences in calculated values of spectral estimates.