The kinetic energy spectrum and general circulation of the atmosphere in a GCM without eddy-eddy interactions

The troposphere exhibits motions at large scales that are characterized by a kinetic energy spectrum with a -3 power-law range. This is commonly explained as an effect of interactions between eddies of different length scales in a nonlinear process known as an enstrophy cascade. It has been unclear to what extent the shape of the energy spectrum is determined by these eddy-eddy interactions, as other effects such as conversion from potential to kinetic energy are known to be important at all length scales. Here we show that the energy spectrum retains its shape in a general circulation model (GCM) of the atmosphere in which interactions between eddies and the mean flow are retained, but eddy-eddy interactions are removed. The length scale at the maximum of the energy spectrum remains the same, suggesting that eddy-eddy interactions are not important in setting the eddy length scale. That the power-law range does not require eddy-eddy interactions is a surprising result that motivates a reassessment of theories of the atmospheric energy spectrum. Eddy-eddy interactions do play a role in isotropizing the eddies, and changes are seen in mean circulation statistics such as the mean zonal wind. Further characterization of the role of eddy-eddy interactions may allow the construction of fast mean-field based models of the atmosphere.