Non-ideal MHD Properties of Magnetic Flux Tubes in the Solar Photosphere

TL;DR

This paper investigates the non-ideal magnetohydrodynamic behavior of solar magnetic flux tubes in the photosphere, revealing an inflow of material and angular velocity deviations crucial for understanding small-scale solar magnetic structures.

Contribution

It introduces a new scaling law showing the significance of inflow effects in small-scale flux tubes passing through the non-ideal photospheric region.

Findings

Inflow of photospheric material into flux tubes is necessary for equilibrium.

Deviations from iso-rotation occur along the flux tube axis.

Effects are negligible for thick tubes but significant for small-scale structures.

Abstract

Magnetic flux tubes reaching from the solar convective zone into the chromosphere have to pass through the relatively cool, and therefore non-ideal (i.e. resistive) photospheric region enclosed between the highly ideal sub-photospheric and chromospheric plasma. It is shown that stationary MHD equilibria of magnetic flux tubes which pass through this region require an inflow of photospheric material into the flux tube and a deviation from iso-rotation along the tube axis. This means that there is a difference in angular velocity of the plasma flow inside the tube below and above the non-ideal region. Both effects increase with decreasing cross section of the tube. Although for characteristic parameters of thick flux tubes the effect is negligible, a scaling law indicates its importance for small-scale structures. The relevance of this "inflow effect" for the expansion of flux tubes above the photosphere is discussed.