The Role of Inertia-Gravity Waves in the Mesoscale Energy Transfers from Global Storm-Resolving Simulations

This study investigates the spectral energy budget of the atmosphere using storm-resolving simulations from two state-of-the-art global circulation models. We examine different hypotheses to explain the mesoscale κ^-5/3 spectrum of horizontal kinetic energy (HKE). These hypotheses include the direct forcing due to inertia-gravity waves (IGWs), a downscale cascade mediated by weakly interacting IGWs, or interactions between waves and the mean flow. The resolved mesoscale energy fluxes within the upper troposphere and the lower stratosphere reveal different dynamics between the two layers. The lower stratosphere is mainly energized by direct forcing due to vertically propagating IGWs, with a negligible HKE cascade. The primary contribution to the mesoscale energy spectrum in the troposphere is from spectral transfers across scales, while the direct forcing due to IGWs is limited. However, the normal mode decomposition of the circulation into linear Rossby waves and IGWs suggests that their interactions dominate the downscale cascade at mesoscales. This result aligns with the hypotheses that explain the downscale cascade based on resonant triad interactions between vortical and gravity-wave modes. Furthermore, it is shown that wave-wave interactions do not contribute to the resolved energy transfers, challenging the hypothesis that the downscale cascade is due to weakly nonlinearly interacting IGWs.