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Generation of electric currents via neutral-ion drag in the chromosphere and ionosphere

Abstract : We consider the generation of electric currents in the solar chromosphere. The ionization level in this region is generally supposed to be low. We show that the ambient electrons are magnetized even for weak magnetic fields (30 G), i.e. their gyrofrequency is larger than the collision frequency; ion motions continue to be dominated by ion-neutral collisions in this region. Under such conditions the ions are dragged by neutrals. As a result, the dynamics of magnetic field resembles frozen-in motion of the field with the neutral gas. On the other hand magnetized electrons drift under the action of the electric and magnetic fields induced in the reference frame of ions moving with the neutral gas. This relative motion of electrons and ions results in the generation of quite intense electric currents. The dissipation of these currents leads to the resistive electron heating and efficient gas ionization. Ionization by electron-neutral impact does not alter the dynamics of the heavy particles; thus the gas turbulent motions persist even when the plasma becomes fully ionized and the resistive current dissipation continues to heat electrons and ions. This heating process is so efficient that it can result in typical temperature increases with altitude as large as 0.1–0.3 eV/km. We conclude that this process can play a major role in the heating of the chromosphere and corona. We show that the physical conditions in the solar chromosphere, in particular the neutral and ion density dependencies upon altitude, are very similar to those in the lower ionosphere of the Earth. A very similar process of current generation occurs in the ionosphere after strong earthquakes, resulting in the generation of strong perturbations in the ionosphere. We then present well-known results of the observations of such perturbations, which allow an evaluation of the increment of the growth of the perturbations with altitude, making use of ionospheric sounding. These results are in perfect agreement with estimates obtained making use a model similar to ours. We consider that these observations clearly show the efficiency of the physical mechanisms discussed, and thus provide strong support for our ideas.
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Vladimir Krasnoselskikh, W.P. Abbett, H. Hudson, G. Vekstein, S.D. Bale. Generation of electric currents via neutral-ion drag in the chromosphere and ionosphere. AIP Conference Proceedings, 2012, Eilat, Israel. pp.42-62, ⟨10.1063/1.3701350⟩. ⟨insu-02927191⟩

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