Nonlinear wave structures in collisional plasma of auroral E-region ionosphere

摘要

Studies of the auroral plasma withsmall-scale inhomogenieties producing the VHF-radar reflections (radar aurora)when observed in conditions of the saturated Farley-Buneman instability withinthe auroral E region, show strong nonlinear interactions and densityfluctuations of 5–15%. Such nonlinearity and high fluctation amplitudes areinconsistent with the limitations of the weak turbulence theory, and thus atheory for arbitrary amplitudes is needed. To this end, a nonlinear theory isdescribed for electrostatic MHD moving plasma structures of arbitrary amplitudefor conditions throughout the altitude range of the collisional auroral Eregion. The equations are derived, from electron and ion motion self-consistentwith the electric field, for the general case of the one-dimensional problem.They take into account nonlinearity, electron and ion inertia, diffusion,deviation from quasi-neutrality, and dynamical ion viscosity. The importance ofthe ion viscosity for dispersion is stressed, while deviation from thequasi-neutrality can be important only at rather low plasma densities, nottypical for the auroral E region. In a small amplitude limit these equationshave classical nonlinear solutions of the type of "electrostatic shockwave" or of knoidal waves. In a particular case these knoidal waves degradeto a dissipative soliton. A two-dimensional case of a quasi-neutral plasma isconsidered in the plane perpendicular to the magnetic field by way of thePoisson brackets, but neglecting the nonlinearity and ion inertia. It is shownthat in these conditions an effective saturation can be achieved at thestationary turbulence level of order of 10%.