Frequency power spectrum of the longitudinal (acoustic) wave-energy flux F_long (left) and the transverse (Alfvén) wave-energy flux F_tran (right), versus height (in both cases normalised by the maximum transverse PS at each height). Coloured lines are over-plotted showing the average energy flux versus height for four frequency ranges and their total. Grey lines show the other wave flux averages for comparison. The upper-convection zone is a source of both longitudinal and transverse waves, with the longitudinal waves having an energy flux that is 2–3 orders of magnitude larger than the transverse waves. However, the longitudinal wave-energy flux decays exponentially with height. Such that in the low corona, the relative balance of energies is reversed.