On the relationship between mixing length and strong turbulence estimates for transport due to drift turbulence

For a simple two-dimensional nonlinear model of the collisional drift instability the relationship between mixing length and strong turbulence fluxes investigated. Calculation of the turbulent wavenumber spectrum within a strong turbulence model shows that the transport is dominated by an inertial range contribution; this yields a similar result for the fluxes to that from an improved mixing length theory. The nature of the spectrum in the dissipation region, where collisional viscosity dominates, provides an explanation of an apparent paradox that arises when transport fluxes are cast in a form proportional to viscosity (or the diffusion coefficient).