The status of observations and theory of high latitude ionospheric and magnetospheric plasma turbulence

A review is given for the current status of both observations and theory of high-latitude ionospheric plasma turbulence. The principal purpose of this review is to draw connections between the existing body of experimental evidence of fluidlike plasma turbulence in the ionosphere and the predictions of various fluid plasma models that have been proposed to describe the dynamics of the turbulent ionosphere. To place the ionospheric problem in perspective, a tutorial summary of three- and two-dimensional turbulent cascade theory is included along with citations of its applications in neutral fluid turbulence and the supportive experimental evidence found mainly in atmospheric flows. The high-latitude observational evidence for low-frequency ( omega < Omega sub(i) ) macroscale (L > rho sub(i) ) turbulence is summarized. The evidence includes observations of irregularities that occur over an altitude range of 400-8000 km, or possibly higher, and vary over scale sizes of 5 m ( rho sub(i) ) to similar to 2000 km. At the shorter wavelengths, the irregularities are known to be nonpropagating; hence, convective nonlinear processes are important, which suggests that turbulence is the rule. The mathematical description of the turbulent dynamics of much of the ionosphere is suggested to be embodied in a low-frequency fluid model, the essential features of which have been discussed in the literature. Application of standard cascade theory to this model leads to testable predictions of the power spectra for the density and electric field. A comparison of the spectral theory and the observations indicates significant agreement in some cases and ambiguity in others, but no apparent contradictions. Suggestions are made for future experimental diagnostics which could resolve ambiguities.