Spatio-temporal evolution of Hanle and Zeeman synthetic polarization in a chromospheric spectral line

Abstract

Due to the quick evolution of the solar chromosphere, its magnetic field cannot be inferred reliably without accounting for the temporal variations of its polarized light. This has been broadly overlooked in the modelling and interpretation of the polarization due to technical problems (e.g., lack of temporal resolution or of time-dependent MHD solar models) and/or because many polarization measurements can apparently be explained without dynamics. Here, we show that the temporal evolution is critic for explaining the spectral-line scattering polarization because of its sensitivity to rapidly-varying physical quantities and the possibility of signal cancellations and attenuation during extended time integration. For studying the combined effect of time-varying magnetic fields and kinematics, we solved the 1.5D NLTE problem of the second kind in time-dependent 3D R-MHD solar models and we synthesized the Hanle and Zeeman polarization in forward scattering for the chromospheric λ4227 line. We find that the quiet-sun polarization amplitudes depend on the periodicity and spectral coherence of the signal enhacements produced by kinematics, but that substantially larger linear polarization signals should exist all over the solar disk for short integration times. The spectral morphology of the polarization is discussed as a combination of Hanle, Zeeman, dynamic effects and partial redistribution. We give physical references for observations by degrading and characterizing our slit time-series in different spatio-temporal resolutions. The implications of our results for the interpretation of the second solar spectrum and for the investigation of the solar atmospheric heatings are discussed.

arXiv comment16 pages, 14 figures, accepted for publication in ApJ (sent in Nov 2016)

References in corpus (17)

• The stellar atmosphere simulation code Bifrost
• A publicly available simulation of an enhanced network region of the Sun
• RH 1.5D: a massively parallel code for multi-level radiative transfer with partial frequency redistribution and Zeeman polarisation
• Three-dimensional non-LTE radiative transfer computation of the Ca 8542 infrared line from a radiation-MHD simulation
• Fast approximation of angle-dependent partial redistribution in moving atmospheres
• PCA detection and denoising of Zeeman signatures in stellar polarised spectra
• Three-dimensional radiative transfer simulations of the scattering polarization of the hydrogen Ly$\alpha$ line in a MHD model of the chromosphere-corona transition region
• The Hanle and Zeeman polarization signals of the solar Ca II 8542 Å line
• Scattering Polarization and Hanle Effect in Stellar Atmospheres with Horizontal Inhomogeneities
• Scattering polarization in the CaII Infrared Triplet with Velocity Gradients
• Temporal Evolution of the Scattering Polarization of the CaII IR Triplet in Hydrodynamical Models of the Solar Chromosphere
• Chromospheric diagnosis with Ca II lines: forward modeling in forward scattering (I)
• Center to limb observations and modeling of the Ca I 4227 A line
• Observations of the forward scattering Hanle effect in the Ca i 4227 Å line
• Origin of spatial variations of scattering polarization in the wings of the Ca {\sc i} 4227 Åline
• The quantum interference effects in the Sc II 4247 A line of the Second Solar Spectrum
• The key role of solar dynamics in the chromospheric Hanle polarization

Cited by in corpus (10)

• The European Solar Telescope
• The effects of three-dimensional radiative transfer on the resonance polarization of the Ca I 4227 $\mathring{\mathrm{A}}$ line
• Magneto-optical effects in the scattering polarization wings of the Ca I resonance line at 4227 angstroms
• Diagnostic capabilities of spectropolarimetric observations for understanding solar phenomena I. Zeeman-sensitive photospheric lines
• Modeling the scattering polarization of the solar Ca i 4227 Å line with angle-dependent partial frequency redistribution
• Formal Solutions for Polarized Radiative Transfer. IV. Numerical Performances in Practical Problems
• Comparison of theoretical and observed Ca~{\sc ii}~8542 Stokes profiles in quiet regions at the centre of the solar disc
• Assessment of the CRD approximation for the observer's frame RIII redistribution matrix
• Spectropolarimetric observations of the solar atmosphere in the H$\alpha$ 6563 Å line
• Formation and morphology of anomalous solar circular polarization