Numerical Measurement of the Turbulent Response in Drift Alfvén Turbulence, Eduardo Fernandez and P.W. Terry, to be presented at 1996 APS Division of Plasma Physics Meeting.
A model that augments 2D RMHD with drift wave dynamics is studied numerically using a pseudo-spectral code and a variety of numerical diagnostics. The main focus is to verify a prediction that slow fluid advection, rather than rapid Alfvénic decorrelation, determines energy transfer rates when dynamically active density fluctuations are present. Simulations of stationary turbulence driven at long wavelengths and damped at short wavelengths reveal Alfvénic signatures in the frequency spectrum, with counter propagating Alfvén waves the dominant feature, and in the rough equipartition of energies. To determine if the slow timescale fluid straining decorrelation affects spectral transfer the turbulent response function is measured from a statistical ensemble of responses to small perturbations applied to individual modes. The turbulent response is characterized by a transient Alfvénic decorrelation followed by a slow (eddy turnover) timescale feature that dominates time asymptocially. The decorrelation times of both features and their characteristic energy partitions agree quantitatively with theory. These results indicate that the 3/2 spectrum index of Iroshnikov-Kraichnan does not hold for drift Alfvén turbulence, consistent with observations in MST and in the interstellar medium.