Farley-Buneman Instability in the Solar Chromosphere

Abstract

The Farley-Buneman instability is studied in the partially ionized plasma of the solar chromosphere taking into account the finite magnetization of the ions and Coulomb collisions. We obtain the threshold value for the relative velocity between ions and electrons necessary for the instability to develop. It is shown that Coulomb collisions play a destabilizing role in the sense that they enable the instability even in the regions where the ion magnetization is greater than unity. By applying these results to chromospheric conditions, we show that the Farley-Buneman instability can not be responsible for the quasi-steady heating of the solar chromosphere. However, in the presence of strong cross-field currents it can produce small-scale, ∼ 0.1−3 m, density irregularities in the solar chromosphere. These irregularities can cause scintillations of radio waves with similar wave lengths and provide a tool for remote chromospheric sensing.

Nonlinear equation for Farley–Buneman waves in multispecies plasma

“…The magnitude of the nonlinear coefficients depend on the relative concentration, mass and collision frequencies of ion species as shown in Eq. (36). The situations with several ion species exist in the E-region of the Earth's ionosphere and solar chromosphere.…”

“…In these cases, the wave steepening nonlinear term may result in wave breaking and forming strongly nonlinear singular solutions. It is worth noting that the FB waves in multispecies plasmas have recently been studied in application to the solar physics problems [33][34][35][36]. It has been suggested that FB instability plays an important role in the heating of solar chromosphere [33,34].…”

“…Nonlinear equation (36) can be written in a dimensionless form by introducing the following normalized quantities:…”

The ion-acoustic instability in the pre-flare plasma near the loop footpoints at solar active regions

“…Another way is to find an instability with threshold which is much less than the threshold of the ion-acoustic instability (see e.g. Galeev et al, 1972;Duijveman et al, 1981;Somov et al, 1987;Voitenko and Goossens, 2002;Kryshtal and Gerasimenko, 2004;Fontenla et al, 2008;Gogoberidze et al, 2009;Kryshtal et al, 2012, for details). Under some conditions these instabilities can transform into weak and then later into saturated turbulence.…”

“…Later, FBI was investigated further in order to obtain the revised semi-empirical models of the solar chromosphere, which vary from the quiet solar atmosphere Vernazza-Avrett-Loeser (VAL) and more recent FontenlaAvrett-Loeser (FAL) models (see Fontenla et al, 2008Fontenla et al, , 1993Vernazza et al, 1981). The generation mechanism of smallscale density irregularities in the partially ionized plasma of the solar chromosphere by FBI was reported by Gogoberidze et al (2009). These small-scale irregularities can be used for remote diagnostics of strong cross-field currents in the solar chromosphere.…”