An electron thermal diffusion instability and type-3 echoes in the auroral E-region plasma

Details An electron thermal diffusion instability and type-3 echoes in the auroral E-region plasma An electron thermal diffusion instability and type-3 echoes in the auroral E-region plasma

Jan 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995angeo..13...45s&link_type=abstract

Annales Geophysicae (ISSN 0992-7689), vol. 13, no. 1, p. 45-55

Computer Science

Numerical Analysis

10

Acoustic Velocity, Atmospheric Models, Auroral Echoes, Auroral Electrojets, Auroral Zones, E Region, Electron Diffusion, Plasma Waves, Thermal Diffusion, Auroral Spectroscopy, Backscattering, Doppler Radar, Numerical Analysis, Radar Echoes, Spectral Signatures, Wave Propagation

Scientific paper

The observationsl evidence on type-3 radar auroral irregulatities, which are characterized by a Doppler spectrum signature with a narrow peak below ion acoustic speeds, indicates that this coherent scatter is generated under uncommon auroral plasma conditions. In an effort to understand the physics of type-3 radar aurora, we introduce a plasma instability process based on linearized fluid theory and operating during strong electron gas heating events. In these conditions, in addition to the standard terms in the momentum and continuity equations, the model includes a thermal force proportional to B x Del T(sub e) in the electron momentum equation, and also the energy balance equation for the electrons. This leads to a dispersion relation for low-frequency, meter-scale, plasma waves that require for their excitation threshold velocities well below the ion acoustic speed. In general, this is not a totally new instability for the E-region plasma but it relies on a new destabilizing mechanism, that is, strong electron thermal diffusion. Under the widely used assumption that the waves generated propagate at threshold velocities, numerical results show the phase velocities of the waves to be relatively invariant inside the unstable layer of the heated region which, in turn, leads to a narrow spectrum at sub-ion acoustic Doppler velocities. In this paper, we discuss the theory as well as the physical nature of the destabilizing process, and obtain theoretical predictions at instability threshold conditions. It is shown that the electron thermal diffusion instability mechanism can account for several of the type-3 radar auroral properties.

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