Hayashi, Y., and D. G. Golder, 1983: Transient planetary waves simulated by GFDL spectral general circulation models. Part 2: Effects of nonlinear energy transfer. Journal of the Atmospheric Sciences, 40 (4), 951-957.

Abstract: In order to study how transient planetary waves in the midlatitude troposphere are maintained, a space-time spectral analysis over a 1-year data set is made of a GFDL spectral general circulation model.
It is found that the kinetic energy (K_n) of both westward and eastward moving ultralong waves with periods less than 20 days is maintained primarily through conversion from wave available-potential energy (A_n).
In particular, A_n of the westward moving ultralong waves is comparable to that of K_n and is maintained primarily through the wave-wave transfer of A_n. In contrast, A_n of the eastward moving ultralong waves is larger than K_n and is maintained primarily through the zonal-wave transfer of A_n and partly through the wave-wave transfer of A_n. These conclusions also hold in the absence of stationary-transient wave interactions as confirmed by a model with a uniform surface.