Speaker
Description
Co-author: Sebastien Gome
Abstract: Turbulence is characterized by energy fluxes, whose direction is determined by conservation laws.
In 3D rotating turbulence, however, energy is observed to flow simultaneously toward large-scale two-dimensional structures and toward small-scale three-dimensional waves. Using a mean–wave kinetic theory, we derive analytical expressions for these competing bi-directional transfers in the presence of a spontaneously emergent 2D mean flow. We show the direction of the energy transfer is determined by the type of allowed 2D-3D interactions: the mean flow is fed by a sector of modes for which only same-sign-helicity interactions are allowed, while modes which have helicity-mixing interactions extract energy from it. The balance between the two sectors changes as the Rossby- and Reynolds-numbers are varied. We obtain the 2D-3D energy partition as a function of Rossby and Reynolds analytically, in agreement with fully nonlinear simulations, presenting a unified picture across rotation rates.