On the double cascade of energy and enstrophy in QG turbulence

In Quasi-Geostrophic turbulence with finite ultraviolet sink of energy, there exist in general a double cascade of energy and enstrophy both downscale and upscale. Both cascades provide contributions to the energy spectrum that combine linearly, despite the nonlinearity of the governing equations. In 2D turbulence governed by the Navier-Stokes equation a mathematical constraint prevents the contribution of the downscale energy cascade from becoming dominant in the inertial range. However, in baroclinic QG models, this mathematical constraint is violated. Physical implications are discussed.