TY - JOUR
T1 - Comparison of inversion codes for polarized line formation in MHD simulations : I. Milne-Eddington codes
AU - Borrero, J. M.
AU - Lites, B. W.
AU - Lagg, A.
AU - Rezaei, R.
AU - Rempel, M.
N1 - Funding Information:
This research has been carried out in the frame of the two meetings held in February 2010 and December 2012 at the International Space Science Institute (ISSI) in Bern (Switzerland) as part of the International Working group Extracting Information from spectropolarimetric observations: comparison of inversion codes. We are particularly grateful to Dr. Maurizio Falanga, Andrea Fischer and Jennifer Zaugg for their hospitality and help organizing the meetings. Discussions with Drs. Michiel van Noort, Arturo López, Andrés Asensio Ramos, Héctor Socas-Navarro, and Nikola Vitas are also greatfully acknowledged. R.R. acknowledges financial support by DFG grant RE 3282/1-1. This work has made use of the NASA Astrophysical Data System. The National Center for Atmospheric Research is sponsored by the National Science Foundation. This investigation is based on work supported by the National Science Foundation under Grant numbers 0711134, 0933959, 1041709, and 1041710 and the University of Tennessee through the use of the Kraken computing resource at the National Institute for Computational Sciences ( http://www.nics.tennessee.edu ).
Publisher Copyright:
© ESO 2014.
PY - 2014/12/1
Y1 - 2014/12/1
N2 - Milne-Eddington (M-E) inversion codes for the radiative transfer equation are the most widely used tools to infer the magnetic field from observations of the polarization signals in photospheric and chromospheric spectral lines. Unfortunately, a comprehensive comparison between the different M-E codes available to the solar physics community is still missing, and so is a physical interpretation of their inferences. In this contribution we offer a comparison between three of those codes (VFISV, ASP/HAO, and HeLIx+). These codes are used to invert synthetic Stokes profiles that were previously obtained from realistic non-grey three-dimensional magnetohydrodynamical (3D MHD) simulations. The results of the inversion are compared with each other and with those from the MHD simulations. In the first case, the M-E codes retrieve values for the magnetic field strength, inclination and line-of-sight velocity that agree with each other within σB ≤ 35 (Gauss), σγ ≤ 1.2°, and σv ≤ 10 ms-1, respectively. Additionally, M-E inversion codes agree with the numerical simulations, when compared at a fixed optical depth, within σB ≤ 130 (Gauss), σγ ≤ 5°, and σv ≤ 320 ms-1. Finally, we show that employing generalized response functions to determine the height at which M-E codes measure physical parameters is more meaningful than comparing at a fixed geometrical height or optical depth. In this case the differences between M-E inferences and the 3D MHD simulations decrease to σB ≤ 90 (Gauss), σγ ≤ 3°, and σv ≤ 90 ms-1.
AB - Milne-Eddington (M-E) inversion codes for the radiative transfer equation are the most widely used tools to infer the magnetic field from observations of the polarization signals in photospheric and chromospheric spectral lines. Unfortunately, a comprehensive comparison between the different M-E codes available to the solar physics community is still missing, and so is a physical interpretation of their inferences. In this contribution we offer a comparison between three of those codes (VFISV, ASP/HAO, and HeLIx+). These codes are used to invert synthetic Stokes profiles that were previously obtained from realistic non-grey three-dimensional magnetohydrodynamical (3D MHD) simulations. The results of the inversion are compared with each other and with those from the MHD simulations. In the first case, the M-E codes retrieve values for the magnetic field strength, inclination and line-of-sight velocity that agree with each other within σB ≤ 35 (Gauss), σγ ≤ 1.2°, and σv ≤ 10 ms-1, respectively. Additionally, M-E inversion codes agree with the numerical simulations, when compared at a fixed optical depth, within σB ≤ 130 (Gauss), σγ ≤ 5°, and σv ≤ 320 ms-1. Finally, we show that employing generalized response functions to determine the height at which M-E codes measure physical parameters is more meaningful than comparing at a fixed geometrical height or optical depth. In this case the differences between M-E inferences and the 3D MHD simulations decrease to σB ≤ 90 (Gauss), σγ ≤ 3°, and σv ≤ 90 ms-1.
KW - Line: formation
KW - Magnetohydrodynamics (MHD)
KW - Polarization
KW - Radiative transfer
KW - Sun: magnetic fields
KW - Sun: photosphere
UR - http://www.scopus.com/inward/record.url?scp=84913585502&partnerID=8YFLogxK
U2 - 10.1051/0004-6361/201424584
DO - 10.1051/0004-6361/201424584
M3 - Article
AN - SCOPUS:84913585502
SN - 0004-6361
VL - 572
JO - Astronomy and Astrophysics
JF - Astronomy and Astrophysics
M1 - A54
ER -