Farley-Buneman Instability in the Solar Chromosphere

TL;DR

This study analyzes the Farley-Buneman instability in the solar chromosphere, considering ion magnetization and Coulomb collisions, and concludes it cannot cause steady heating but can generate small-scale density irregularities useful for remote sensing.

Contribution

It provides a detailed threshold analysis for the instability in the chromosphere, incorporating finite ion magnetization and Coulomb collisions, which was not thoroughly addressed before.

Findings

Coulomb collisions destabilize the plasma, enabling instability even with high ion magnetization.

The instability cannot account for steady chromospheric heating.

It can produce small-scale density irregularities useful for radio wave scintillation studies.

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, $\sim 0.1-3$ 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.