Global Energetics Analysis by Expansion into Three-Dimensional Normal Mode Functions during the FGGE Winter

Abstract

A diagnostic energetics scheme is developed in order to investigate the energy flows among three-dimensional normal modes (Hough modes in horizontal) in the atmosphere. This scheme is applied to the GFDL version of the FGGE level IIIb data during the winter from December 1978 to February 1979.
The resultant energy flow is summarized as follows: available potential energy generated at zonal baroclinic modes (especially at the vertical mode m=4) is directly converted into kinetic energy of the planetary scale barotropic mode. Kinetic energy of the cyclone scale baroclinic mode is transformed into zonal and eddy kinetic energies of the barotropic mode. Parameterizing the horizontal scale of waves by their eigenfrequencies, we find for vertically trapped modes, the kinetic energy spectrum follows approximately the 3 power of the frequency. However, for the propagative Rossby modes, the spectrum obeys the -5/3 power law and merges continuously with the spectrum of the gravity modes. It is concluded from the results that the energy spectrum depends on the vertical propagation properties; the energy spectrum of the propagative Rossby waves is similar to that of gravity waves in the frequency domain. The trapped and the critical modes gain their energy through the interactions mentioned above, whereas we find the propagative modes lose a part of energy through nonlinear mode-mode interactions.