Mesoscale Spectral Energy Transfers in Global Storm-resolving Simulations

The atmospheric horizontal kinetic energy (HKE) spectrum follows a κ −5/3 power-law at mesoscales (scales ≲ 600 km). The dynamics underlying the observed mesoscale spectrum remain a subject of controversy. The prevailing explanations include a downscale cascade mediated by weakly interacting inertia-gravity waves (IGWs), strongly stratified turbulence, or interactions between IGWs and the geostrophic flow. This study examines the mesoscale spectral energy budgets derived from global storm-resolving simulations conducted using two general circulation models. The mesoscale energy fluxes within the upper troposphere and the lower stratosphere reveal different dynamics regarding the contributions from local forcing and spectral transfers across wavenumbers to the HKE spectrum. The stratosphere is primarily energized by upward-propagating IGWs through the convergence of vertical fluxes. The stratosphere exhibits an upscale spectral transfer mediated by nonlinear interactions between rotational modes. However, this upscale transfer is small compared to the energy deposited by IGWs. The primary contribution to the mesoscale HKE spectrum in the troposphere is from nonlinear spectral HKE transfers towards small scales. Furthermore, decomposing the nonlinear spectral transfers into contributions from Rossby and IGW modes reveals that their interaction dominates the downscale spectral transfer. Moreover, our results suggest that linear interactions between IGW modes do not contribute to the resolved spectral energy transfers.