The key role of solar dynamics in the chromospheric Hanle polarization

TL;DR

This paper demonstrates that accounting for solar atmospheric dynamics is essential for accurately modeling scattering polarization and inferring weak magnetic fields, resolving longstanding discrepancies between theory and observations.

Contribution

It introduces a time-dependent modeling approach that incorporates solar dynamics, enabling better interpretation of polarization signals and magnetic field diagnostics in the chromosphere.

Findings

Reproduces Ca I 4227 Å polarization shapes and amplitudes

Shows dynamics mimic Zeeman linear polarization profiles

Supports time-dependent scattering polarization as a diagnostic tool

Abstract

The quantum theory of polarized light allows one to model scattering in the solar atmosphere for inferring its properties. This powerful approach has revealed two key long-standing problems in solar physics: the puzzling dilemmas between theory and observations in several anomalously polarized spectral lines and the need for inferring the ubiquitous weak chromospheric magnetic fields, which requires discriminating the Hanle effect in dynamic optically thick plasmas. However, the ever-present dynamics, i.e., the temporal evolution of heatings and macroscopic motions, has been widely disregarded when modeling and interpreting the scattering polarization. This has hindered a consistent theoretical solution to the puzzle while falsifying the Hanle diagnosis. Here, we show that the dynamical evolution is a keystone for solving both problems because its systematic impact allows an explanation of the observations from 'anomalous' instantaneous polarization signals. Evolution accounted for, we reproduce amplitudes and (spectral and spatial) shapes of the Ca I 4227 A polarization at solar disk center, identifying a restrictive arrangement of magnetic fields, kinematics, heatings, and spatio-temporal resolution. We find that the joint action of dynamics, Hanle effect, and low temporal resolutions mimics Zeeman linear polarization profiles, the true weak-field Zeeman signals being negligible. Our results allow reinterpretation of many polarization signals of the solar spectra and support time-dependent scattering polarization as a powerful tool for deciphering the spatio-temporal distribution of chromospheric heatings and fields. This approach may be a key aid in developing the Hanle diagnosis for the solar atmosphere.