Internetwork magnetic field distribution from simultaneous 1.56 micron and 630 nm observations

TL;DR

This study compares and combines infrared and visible spectropolarimetric observations to resolve discrepancies in magnetic field strength measurements in the solar internetwork, revealing small-scale magnetic structures and their spatial distribution.

Contribution

The paper presents the first simultaneous inversion of infrared and visible spectropolarimetric data to accurately characterize internetwork magnetic fields.

Findings

Infrared and visible observations trace the same magnetic structures.

Most magnetic flux density is around 10 Mx/cm2 with nearly zero net flux.

Magnetic fields are predominantly sub-kG and located in intergranular lanes.

Abstract

We study the contradictory magnetic field strength distributions retrieved from independent analyses of spectropolarimetric observations in the near-infrared (1.56 micron) and in the visible (630 nm) at internetwork regions. In order to solve this apparent controversy, we present simultaneous and co-spatial 1.56 micron and 630 nm observations of an internetwork area. The properties of the circular and linear polarization signals, as well as the Stokes V area and amplitude asymmetries, are discussed. As a complement, inversion techniques are also used to infer the physical parameters of the solar atmosphere. As a first step, the infrared and visible observations are analysed separately to check their compatibility. Finally, the simultaneous inversion of the two data sets is performed. The magnetic flux densities retrieved from the individual analysis of the infrared and visible data sets are strongly correlated. The polarity of the Stokes V profiles is the same at co-spatial pixels in both wavelength ranges. This indicates that both 1.56 micron and 630 nm observations trace the same magnetic structures on the solar surface. The simultaneous inversion of the two pairs of lines reveals an internetwork full of sub-kG structures that fill only 2 % of the resolution element. A correlation is found between the magnetic field strength and the continuum intensity: equipartition fields (B ~500 G) tend to be located in dark intergranular lanes, whereas weaker field structures are found inside granules. The most probable unsigned magnetic flux density is 10 Mx/cm2. The net magnetic flux density in the whole field of view is nearly zero. This means that both polarities cancel out almost exactly in our observed internetwork area.