Dataset for "Helicity proxies from linear polarisation of solar active regions"
DOI10.5281/zenodo.3888575Zenodo3888575MaRDI QIDQ6722090
Dataset published at Zenodo repository.
Author name not available (Why is that?)
Publication date: 10 June 2020
Copyright license: No records found.
The \(\alpha\)effect is believed to play a key role in the generationof the solar magnetic field. A fundamental test for its significance inthe solar dynamo is to look for magnetic helicity of opposite signsin the two hemispheres, and at small and large scales. However, measuring magnetic helicity is compromised by the inability to fully infer themagnetic field vector from observations of solar spectra,caused by what is known as the \(\pi\)ambiguity ofspectropolarimetric observations.We decompose linear polarisation into parity-even and parity-odd E and B polarisations,which are not affected by the \(\pi \) ambiguity.Furthermore, we study whether the correlations of spatial Fourierspectra of Band parity-even quantities such as Eortemperature T are a robust proxy for magnetic helicity of solar magnetic fields. We analyse polarisation measurements of active regions observed by theHelioseismic and Magnetic Imager on board the Solar Dynamics observatory. Theory predictsthe magnetic helicity of active regions to have, statistically, opposite signs in the two hemispheres.We then compute the parity-odd EB and TB correlations, and test for systematic preference oftheir sign based on the hemisphere of the active regions.We find that: (i) EB and TB correlations are a reliable proxy for magnetic helicity, whencomputed from linear polarisation measurements away from spectral line cores, and (ii)Epolarisation reverses its sign close to the line core. Our analysis reveals Faradayrotation to not have a significant influence on the computed parity-odd correlations.The EBdecomposition of linear polarisation appears to be a good proxy for magnetic helicityindependent of the \(\pi\)ambiguity. This allows us to routinely infer magnetic helicitydirectly from polarisation measurements. The full article can be found athttps://arxiv.org/abs/2001.10884
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