Inferring the magnetic field vector in the quiet Sun

Borrero, J. M.; Kobel, Philippe

doi:10.1051/0004-6361/201118238

Cited by 36 publications

(21 citation statements)

References 27 publications

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“…Up to 75 % of the observed Q signals are below this level and thus presumably correspond to noise (see also Borrero & Kobel 2012). The observed distributions of maximal Stokes Q at 630.15 nm and 630.25 nm match those of the 20 G h run for small polarization amplitudes below the 3-σ level.…”

Section: Sp Map (0supporting

confidence: 55%

The Polarization Signature of Photospheric Magnetic Fields in 3D MHD Simulations and Observations at Disk Center

Beck

Fabbian

Rezaei

et al. 2017

ApJ

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Before using three-dimensional (3D) magneto-hydrodynamical (MHD) simulations of the solar photosphere in the determination of elemental abundances, one has to ensure that the correct amount of magnetic flux is present in the simulations. The presence of magnetic flux modifies the thermal structure of the solar photosphere, which affects abundance determinations and the solar spectral irradiance. The amount of magnetic flux in the solar photosphere also constrains any possible heating in the outer solar atmosphere through magnetic reconnection. We compare the polarization signals in disk-center observations of the solar photosphere in quiet-Sun regions with those in Stokes spectra computed on the basis of 3D MHD simulations having average magnetic flux densities of about 20, 56, 112 and 224 G. This approach allows us to find the simulation run that best matches the observations. The observations were taken with the Hinode SpectroPolarimeter (SP), the Tenerife Infrared Polarimeter (TIP), the Polarimetric Littrow Spectrograph (POLIS) and the GREGOR Fabry-Pèrot Interferometer (GFPI), respectively. We determine characteristic quantities of full Stokes profiles in a few photospheric spectral lines in the visible (630 nm) and near-infrared (1083 and 1565 nm). We find that the appearance of abnormal granulation in intensity maps of degraded simulations can be traced back to an initially regular granulation pattern with numerous bright points in the intergranular lanes before the spatial degradation. The linear polarization signals in the simulations are almost exclusively related to canopies of strong magnetic flux concentrations and not to transient events of magnetic flux emergence. We find that the average vertical magnetic flux density in the simulation should be less than 50 G to reproduce the observed polarization signals in the quiet Sun internetwork. A value of about 35 G gives the best match across the SP, TIP, POLIS and GFPI observations.

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Section: Sp Map (0supporting

confidence: 55%

The Polarization Signature of Photospheric Magnetic Fields in 3D MHD Simulations and Observations at Disk Center

Beck

Fabbian

Rezaei

et al. 2017

ApJ

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“…The inclination angles display the same morphology in the distribution plots, but the HMI data generally fail to achieve the extreme inclination angles at all flux densities and tend to lie closer to the plane of the sky. This again may be a consequence of scattered light (LaBonte, 2004b) or noise (Borrero and Kobel, 2011), or it may be attributable to the better wavelength sampling of Hinode/SP, which effectively leads to an enhanced signal-to-noise ratio.…”

Section: Hmi Vector Magnetograms Vs Hinode/sp Vector Magnetogramsmentioning

confidence: 99%

The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Overview and Performance

et al. 2014

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The Helioseismic and Magnetic Imager (HMI) began near-continuous full-disk solar measurements on 1 May 2010 from the Solar Dynamics Observatory (SDO). An automated processing pipeline keeps pace with observations to produce observable quantities, including the photospheric vector magnetic field, from sequences of filtergrams. The basic vector-field frame list cadence is 135 seconds, but to reduce noise the filtergrams are combined to derive data products every 720 seconds. The primary 720 s observables were released in mid-2010, including Stokes polarization parameters measured at six wavelengths, as well as intensity, Doppler velocity, and the line-of-sight magnetic field. More advanced products, including the full vector magnetic field, are now available. Automatically identified HMI Active Region Patches (HARPs) track the location and shape of magnetic regions throughout their lifetime.The vector field is computed using the Very Fast Inversion of the Stokes Vector (VFISV) code optimized for the HMI pipeline; the remaining 180 • azimuth ambiguity is resolved with the Minimum Energy (ME0) code. The Milne-Eddington inversion is performed on all full-disk HMI observations. The disambiguation, until recently run only on HARP regions, is now implemented for the full disk. Vector and scalar quantities in the patches are used to derive active region indices potentially useful for forecasting; the data maps and indices are collected in the SHARP data series, hmi.sharp_720s. Definitive SHARP processing is completed only after the region rotates off the visible disk; quick-look products are produced in near real time. Patches are provided in both CCD and heliographic coordinates.HMI provides continuous coverage of the vector field, but has modest spatial, spectral, and temporal resolution. Coupled with limitations of the analysis and interpretation techniques, effects of the orbital velocity, and instrument performance, the resulting measurements have a certain dynamic range and sensitivity and are subject to systematic errors and uncertainties that are characterized in this report.

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“…Histogram of the magnetic filling factor derived from the weak field laws following the method described in Bommier et al [2009]. The pixel selection of linear polarization spectral maximum larger than 4.5 times the polarimetric noise level was performed following Borrero and Kobel [2012]. Figure 6.…”

Section: Application: Flux Tube Diameter Inferred From Spatial Correlmentioning

confidence: 99%

Milne‐Eddington inversion for unresolved magnetic structures in the quiet Sun photosphere

Bommier

2016

JGR Space Physics

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This paper is first devoted to present our method for modeling unresolved magnetic structures in the Milne‐Eddington inversion of spectropolarimetric data. The related definitions and other approaches and different used inversion algorithms are recalled for comparison. In a second part, we apply our method to quiet Sun data outside active regions. We obtain the quiet Sun photospheric magnetic field as composed of unresolved opening and connected magnetic flux tubes, which form a loop carpet of field lines. We then analyze the spatial correlation, which we also observed for the magnetic field vector, in terms of flux tube diameter, distance, and field strength. We find that different observations with the Zurich imaging polarimeter and THEMIS polarimeter mounted on the THEMIS telescope give very close results, and we add results also very close derived from HINODE/Solar Optical Telescope/spectropolarimeter observations analyzed with the same method. We obtain a mean flux tube diameter of 30 km, a mean flux tube distance of 230 km, and a mean flux tube magnetic field of 1.3 kG.

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Inferring the magnetic field vector in the quiet Sun

Cited by 36 publications

References 27 publications

The Polarization Signature of Photospheric Magnetic Fields in 3D MHD Simulations and Observations at Disk Center

The Polarization Signature of Photospheric Magnetic Fields in 3D MHD Simulations and Observations at Disk Center

The Helioseismic and Magnetic Imager (HMI) Vector Magnetic Field Pipeline: Overview and Performance

Milne‐Eddington inversion for unresolved magnetic structures in the quiet Sun photosphere

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