Spectral evidence for stirring scales and two‐dimensional turbulence in the auroral ionosphere

Abstract

Electric field power spectra from two auroral sounding rocket flights show evidence of a distinct scale size regime for injection of energy into the auroral oval. The signature of this process is a broad plateau in the spectrum, with power law dependences at both shorter and longer scale sizes. We argue that the spectral properties at high k are dominated by processes occurring near the edges of inverted‐V electron precipitation regions (auroral arcs) We see no compelling reason to conclude that a linear local plasma instability is occurring but rather, that nonlinear mixing and forward cascade yield the observed velocity field. The spectra of simultaneously observed density irregularities are quite different from those of the electric field, implying that the plasma density does not behave as a passive scalar in the auroral zone during active conditions. At low‐k values we show that the rocket spectra are consistent with the power spectra of magnetospheric electric fields measured by the DE, AE‐C, and Hilat stallites.