Multi-height probing of horizontal flows in the solar photosphere

Abstract

We tested whether simultaneous spectropolarimetric imaging in two magnetically sensitive optical spectral lines, which probe two different layers of the solar atmosphere (the photosphere and the temperature minimum), can help constrain the depth variation of horizontal flows. We first tested the feasibility of our method using Fourier local correlation tracking (FLCT) to track physical quantities at different optical depths ($\log {\tau }_{500}=-1,-2,-3,-4$) in an atmosphere simulated with the MURaM code. We then inferred the horizontal distribution of the LOS magnetic field component from synthetic spectropolarimetric observations of Fe I 525.0 nm and Mg I b2 spectral lines, applied FLCT to the time sequence of these synthetic magnetograms, and compared our findings with the original height-dependent horizontal velocities. Tracking the LOS magnetic field component (which coincides with the vertical component at the disk center) yields horizontal velocities that, after appropriate temporal and spatial averaging, agree excellently with the horizontal component of the simulated velocities, both calculated at constant ${\tau }_{500}$ surfaces, up to the temperature minimum ($\log {\tau }_{500}=-3$). When tracking the temperature at constant ${\tau }_{500}$ surfaces, this agreement already breaks down completely at the mid photosphere ($\log {\tau }_{500}=-2$). Tracking the vertical component of the magnetic field inferred from synthetic observations of the Fe I 525.0 nm and the Mg I b2 spectral lines yields a satisfactory inference of the horizontal velocities in the mid-photosphere ($\log {\tau }_{500}\approx -1$) and the temperature minimum ($\log {\tau }_{500}\approx -3$), respectively. Our results indicate that high-spatial-resolution spectropolarimetric imaging in solar spectral lines can provide meaningful information about the horizontal plasma velocities over a range of heights.

abstract modified to fit arXiv requirements; 11 pages, 11 figures; accepted for publishing in A&A

References in corpus (14)

• CRISP Spectropolarimetric Imaging of Penumbral Fine Structure
• Numerical simulations of quiet Sun magnetism: On the contribution from a small-scale dynamo
• Inversion of the radiative transfer equation for polarized light
• Radiative diagnostics in the solar photosphere and chromosphere
• A Comprehensive Method of Estimating Electric Fields from Vector Magnetic Field and Doppler Measurements
• Instrumentation for solar spectropolarimetry: state of the art and prospects
• Comparison of inversion codes for polarized line formation in MHD simulations. I. Milne-Eddington codes
• Combining magneto-hydrostatic constraints with Stokes profiles inversions
• Observed and Simulated Power Spectra of Kinetic and Magnetic Energy retrieved with 2D inversions
• The influence of NLTE effects in Fe I lines on an inverted atmosphere I. 6301 A and 6302 A lines formed in 1D NLTE
• Thermodynamic Evolution of Solar Flare Supra-arcade Downflows
• Probing the effect of cadence on the estimates of photospheric energy and helicity injections in eruptive active region NOAA AR 11158
• Validation of the PDFI_SS method for electric field inversions using a magnetic flux emergence simulation
• A modified Milne-Eddington approximation for a qualitative interpretation of chromospheric spectral lines