Electric resistivity of partially ionized plasma in the lower solar atmosphere

Abstract

The lower solar atmosphere is a gravitationally stratified layer of partially ionized plasma. We calculate the electric resistivity in the solar photosphere and chromosphere, which is the key parameter that controls the rate of magnetic reconnection in a Sweet-Parker current sheet. The calculation takes into account the collisions between ions and hydrogen atoms as well as the electron-ion collisions and the electron-hydrogen atom collisions. We find that under the typical conditions of the quiet Sun, electric resistivity is determined mostly by the electron-hydrogen atom collisions in the photosphere, and mostly by the ion-hydrogen collisions, i.e. ambipolar diffusion, in the chromosphere. In magnetic reconnection events with strong magnetic fields, the ambipolar diffusion, however, may be insignificant because the heating by the reconnection itself may lead to the full ionization of hydrogen atoms. We conclude that ambipolar diffusion may be the most important source of electric resistivity responsible for the magnetic flux cancelation and energy release in chromospheric current sheets that can keep a significant fraction of neutral hydrogen atoms.

Height-dependent differential rotation of the solar atmosphere determined by the CHASE spectroscopic observation

“…Therefore, the ubiquitous small-scale magnetic field anchored beneath the solar surface drive the low-plasma-β chromosphere and corona to rotate faster than the photosphere with high plasma β. It is also noticed that the ionization degree decreases and resistivity increases significantly from the chromosphere to the photosphere [51]. Therefore, we tentatively propose that the slower rotation in the photosphere might be owing to the violation of frozen-in effect of the magnetic field in the lower solar atmosphere.…”

Numerical Studies of Magnetic Reconnection and Heating Mechanisms for the Ellerman Bomb

“…Previous simulations also indicate that Joule heating is very important for converting magnetic energy into heat (Ni et al 2016) in such a dense plasma. The heating caused by ambipolar diffusion can be ignored in a low β reconnection process around the solar TMR (Ni et al 2021(Ni et al , 2022, but it might play a role in a high β reconnection event such as an EB (Chae & Litvinenko 2021). When plasmoid instability appears in the reconnection current sheet, many small scale slow-mode and fast-mode shocks appear inside the plasmoid (Ni et al 2015(Ni et al , 2016, which can also heat plasmas in the reconnection region.…”