Turbulent generation of auroral currents and fields - a spectral simulation of two-dimensional MHD turbulence

The nonlinear evolution of largescale turbulent boundary layer flow with magnetosphere-ionosphere coupling is investigated by a two-dimensional, forced, time-dependent MHD model of the disturbed flux tube. It is suggested that the nonlinear effect, especially the current nonlinear effect, plays an important role in breaking large-scale vortices and currents into medium and small ones. Spectral simulation results show that the large-scale turbulent magnetospheric vortices can be connected with highly structured auroral forms by an energy cascade process. The results are subject to a wavelength-dependent damping rate, which is caused by field-aligned anomalous resistivity and Pedersen conductivity, and fluctuating driving terms (due to, for example, the Kelvin-Helmholtz instability). Our results indicate that the evolution of a disturbed flux tube is determined by the nonlinear effect, the scale length dependence of the damping rate, and the structure of the driving terms.