The Kinetic Energy of Large-Scale Atmospheric Motion in Wavenumber-Frequency Space: 11. Mid-Troposphere of the Southern Hemisphere

The wavenumber-frequency spectra of the kinetic energy of the zonal and meridional components of the motion in the mid-troposphere of the Southern Hemisphere show a definite spectral domain of wave activities. This spectral domain is generally oriented from a region of low wavenumbers and low frequencies to a region of high wavenumber and negative frequencies designated for waves moving from west to east. The wavenumber-frequency spectra of the large-scale motion indicate that wave activities in the summer have the same intensity as in the winter in the Southern Hemisphere, whereas in the Northern Hemisphere the wave intensity in summer is about 50% of that in winter. The frequency spectra of the kinetic energy of the zonal and meridional components of the motion show similar distributions at all latitudes and seasons for the respective components of the motion. In the high-frequency range, the frequency spectra of both the zonal and meridional motion are approximately proportional to the –1 power of the frequency. The wavenumber spectra of the kinetic energy of the zonal and meridional motion also show a similar distribution at all latitudes and seasons for the respective components of the motion. In the high-wave-number range, the spectra of both the zonal and meridional components of the motion are approximately proportional to the –3 power of the wavenumber, which is characteristic of the wavenumber spectrum for the two-dimensional flow of an incompressible viscous fluid. The fact that the wavenumber and frequency spectra are proportional to different powers of wavenumber and frequency indicates that Taylor's transformation does not apply to the large-scale motion in the atmosphere. The mean kinetic energy of the zonal motion in the mid-troposphere of the Southern Hemisphere shows a maximum near 40S in winter and 50S in summer, with 75% of the kinetic energy of the zonal motion being associated with the stationary mean zonal motion and 25% with the zonal component of the moving waves. The mean kinetic energy of the meridional component of the motion shows a maximum at 50S for both the summer and winter seasons. Practically all the kinetic energy of the meridional motion is associated with the moving waves.