The Effect of Eddy-Eddy Interactions on Jet Formation and Macroturbulent Scales

The effect of eddy-eddy interactions on zonal and meridional macroturbulent scales is investigated over a wide range of eddy scales, using high-resolution idealized GCM simulations with and without eddy-eddy interactions. The wide range of eddy scales is achieved through systematic variation of the planetary rotation rate and thus multiple-jet planets. It is found that not only are eddy-eddy interactions not essential for the formation of jets, but the existence of eddy-eddy interactions decreases the number of eddy-driven jets in the atmosphere. The eddy-eddy interactions have little effect on the jet scale, which in both types of simulations coincides with the Rhines scale through all latitudes. The decrease in the number of jets in the presence of eddy-eddy interactions occurs because of the narrowing of the latitudinal region where zonal jets appear. This narrowing occurs because eddy-eddy interactions are mostly important at latitudes poleward of where the Rhines scale is equal to the Rossby deformation radius. Thus, once eddy-eddy interactions are removed, the conversion from baroclinic to barotropic eddy kinetic energy increases, and eddy-mean flow interactions intrude into these latitudes and maintain additional jets there. The eddy-eddy interactions are found to increase the energy-containing zonal scale so it coincides with the jets' scale and thus make the flow more isotropic. While the conversion scale coincides with the most unstable scale, the Rossby deformation radius does not provide a good indication to these scales in both types of simulations.