Nonequilibrium fluctuations of the direct cascade in surface quasi-geostrophic turbulence

Turbulence is by definition an out-of-equilibrium phenomenon, with energy flowing continuously from the large, input scales, to the small, dissipative ones. Temporal fluctuations in this energy flux produce corrections to the Kolmogorov energy spectrum which can be predicted using a multiscale perturbative approach. Here we investigate this problem in the Surface Quasi-Geostrophic model of turbulence, comparing the theoretical predictions with the outcome of high-resolution direct numerical simulations.