Energy Spectra of Rossby and Gravity Waves

The characteristics of energy spectrum based on 3D normal mode energetics are investigated with the global analysis dataset provided by Japan Meteorological Agency (JMA) with the resolution of TL959L60. The energy spectrum of gravity modes exactly follows the -5/3 power law in the synoptic and mesoscales. In the synoptic scale, the spectral slope of total energy follows the -3 power law because Rossby waves are dominant compared to gravity waves. The energy level of gravity modes becomes larger than that of Rossby modes around the zonal wavenumber k = 80. This scale corresponds to 350 km in 45 degrees circle. The total energy spectrum does not show a clear transition from -3 power slope to -5/3 power slope because the energy level of Rossby and gravity modes become comparable near the transition wavenumbers.