NOTES ON THE TRANSFORMATION OF MECHANICAL ENERGY FROM AND TO EDDYING MOTION

Abstract

The equations of mechanical energy of total, mean and eddying motions are derived and discussed. It is shown that, in general, no term of these equations can directly be interpreted as representing the rate of transformation of mechanical energy of mean motion to mechanical energy of the eddying motion. Observational evidence is discussed, showing that the prominent energy transformations in the atmospheric boundary layer stem from the work done by the pressure-gradient force and from the viscous dissipation of energy. The eddy flux of energy of the mean motion and the divergence of this flux act as an intermediary agent between the prominent sources and sinks of energy. A characteristic of the atmosphere is the possibility of “kinetic-energy cycles,” or two-way conversions in which the disturbance can feed into the energy of the mean motion, in contrast to the “energy cascade” from mean to eddy energy of wind-tunnel turbulence.