Non-LTE inversions of a confined X2.2 flare: I. Vector magnetic field in the photosphere and chromosphere

Abstract

Obtaining the magnetic field vector accurately in the solar atmosphere is essential for studying changes in field topology during flares and to reliably model space weather. We tackle this problem by applying various inversion methods to a confined X2.2 flare in NOAA AR 12673 on September 6, 2017, comparing the photospheric and chromospheric magnetic field vector with those from two numerical models of this event. We obtain the photospheric field from Milne-Eddington (ME) and (non-)local thermal equilibrium (non-LTE) inversions of Hinode SOT/SP Fe I 6301.5Å and 6302.5Å. The chromospheric field is obtained from a spatially-regularised weak field approximation (WFA) and non-LTE inversions of Ca II 8542Å observed with CRISP at the Swedish 1-m Solar Telescope. The LTE- and non-LTE-inferred photospheric field components are strongly correlated throughout the atmosphere, with stronger field and higher temperatures in the non-LTE inversions. For the chromospheric field, the non-LTE inversions correlate well with the spatially-regularised WFA. We find strong-field patches of over 4.5 kG in the photosphere, co-located with similar concentrations exceeding 3 kG in the chromosphere. The obtained field strengths are up to 2-3 times higher than in the numerical models, with more concentrated and structured photosphere-to-chromosphere shear close to the polarity inversion line. The LTE and non-LTE Fe I inversions yield essentially the same photospheric field, while ME inversions fail to reproduce the field vector orientation where Fe I is in emission. Our inversions confirm the locations of flux rope footpoints that are predicted by numerical models. However, pre-processing and lower spatial resolution lead to weaker and smoother field in the models than what the data indicate. This emphasises the need for higher spatial resolution in the models to better constrain pre-eruptive flux ropes.

Submitted to Astronomy & Astrophysics. 16 pages, 8 figures

References in corpus (35)

• The Solar Optical Telescope for the Hinode Mission: An Overview
• Astrophysics Source Code Library
• The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: SHARPs -- Space-weather HMI Active Region Patches
• CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
• Preprocessing of vector magnetograph data for a non-linear force-free magnetic field reconstruction
• Solar Flare Prediction Using SDO/HMI Vector Magnetic Field Data with a Machine-Learning Algorithm
• CRISPRED: A data pipeline for the CRISP imaging spectropolarimeter
• The Open Flux Problem
• Non-LTE inversions of the Mg II h&k and UV triplet lines
• Block-induced complex structures building the flare-productive solar active region 12673
• 3D Temperature Mapping of Solar Photospheric Fine Structure Using Ca II H Filtergrams
• Mapping the magnetic field of flare coronal loops
• Spatially-Resolved Nonthermal Line Broadening During The Impulsive Phase of a Solar Flare
• Spectral signatures of chromospheric condensation in a major solar flare
• First Detection of Chromospheric Magnetic Field Changes During an X1-Flare
• A method for global inversion of multi-resolution solar data
• The development of lower-atmosphere turbulence early in a solar flare
• Super-strong Magnetic Field in Sunspots
• Sparse inversion of Stokes profiles. I. Two-dimensional Milne-Eddington inversions
• Flaring Rates and the Evolution of Sunspot Group McIntosh Classifications
• Detection of the strongest magnetic field in a sunspot light bridge
• Spectropolarimetric observations of the Ca II 8498 A and 8542 A lines in the quiet Sun
• Real-time flare prediction based on distinctions between flaring and non-flaring active region spectra
• Inference of the chromospheric magnetic field configuration of solar plage using the Ca II 8542 Å line
• Observed and Simulated Power Spectra of Kinetic and Magnetic Energy retrieved with 2D inversions
• Comparative Study of Data-driven Solar Coronal Field Models Using a Flux Emergence Simulation as a Ground-truth Data Set
• The influence of NLTE effects in Fe I lines on an inverted atmosphere I. 6301 A and 6302 A lines formed in 1D NLTE
• Optimization of Photospheric Electric Field Estimates for Accurate Retrieval of Total Magnetic Energy Injection
• Homologous white light solar flares driven by photosperic shear motions
• Two strong white-light solar flares in AR NOAA 12673 as potential clues for stellar superflares
• Determining the dynamics and magnetic fields in He I 10830 Å during a solar filament eruption
• Magnetic and dynamical photospheric disturbances observed during an M3.2 solar flare
• Superstrong photospheric magnetic fields in sunspot penumbrae
• Intrusion of Magnetic Peninsula toward the Neighboring Opposite-polarity Region That Triggers the Largest Solar Flare in Solar Cycle 24
• Stratification of canopy magnetic fields in a plage region. Constraints from a spatially-regularized weak-field approximation method

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