Inverse cascades in rotating stratified turbulence: Fast growth of large scales

We examine the inverse cascade of kinetic energy to large scales in rotating stratified turbulence as occurs in the oceans and in the atmosphere, while varying the relative frequency of gravity to inertial waves, N/f. Using direct numerical simulations with grid resolutions up to 1024(3) points, we find that the transfer of energy from three-dimensional to two-dimensional modes is most efficient in the range 1/2 <= N/f <= 2, in which resonances disappear. In this range, the cascade is faster than in the purely rotating case, and thus the interplay between rotation and stratification helps creating large-scale structures. The ensuing inverse cascade follows a - 5/3 spectral law with an approximately constant flux. This inverse cascade becomes negligible when stratification is dominant. Copyright (c) EPLA, 2013