Transient Planetary Waves Simulated by GFDL Spectral General Circulation Models. Part II: Effects of Nonlinear Energy Transfer

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 (Kn) of both westward and eastward moving ultralong waves with periods less than 20 days is maintained primarily through conversion from wave available-potential energy (An). In particular, An of the westward moving ultralong waves is comparable to that of Kn and is maintained primarily through the wave-wave transfer of An. In contrast, An of the eastward moving ultralong waves is larger than Kn and is maintained primarily through the zonal-wave transfer of An and partly through the wave-wave transfer of An. These conclusions also hold in the absence of stationary-transient wave interactions as confirmed by a model with a uniform surface.