Nonlinear Energy Transfer between Stationary and Transient Waves Simulated by a GFDL Spectral General Circulation Model

Abstract

A wavenumber spectral analysis has been made of the nonlinear energy transfer between the tropospheric stationary (January mean) and transient waves in the midlatitudes simulated by a GFDL 9-level spectral general circulation model with 30 zonal wavenumbers. It is shown that the wavenumber energy spectrum are fairly well simulated, although the kinetic energy of simulated ultralong waves is about 60% of that observed. In particular, both simulated and observed ultralong waves are maintained primarily by energy transfer from zonal available potential energy. The model?s energy spectra are then partitioned into stationary and transient wave parts. It is found that stationary ultralong waves gain kinetic energy but lose available potential energy through the nonlinear interaction with transient waves. Since this loss is much larger than the gain, transient waves act to destroy stationary wave energy which is maintained primarily by conversion from the zonal available potential energy, being consistent with observations. On the other hand, transient ultralong waves gain both kinetic and available potential energy through wave?wave interactions. This gain is comparable to the gain from the zonal available potential energy.