Computed flat-fields in helioprojective coordinates. Flat-fields taken midway through observation. Used for f-mode pipeline (https://github.com/waledeigt/HSSCaster.git).

Computed flat-fields in helioprojective coordinates. Flat-fields taken midway through observation. Used for f-mode pipeline (https://github.com/waledeigt/HSSCaster.git).

Magnetoconvection at the solar surface governs the dynamics in the upper solar atmosphere and sustains the heliosphere. Properties of this fundamental process are poorly described near the solar poles. Here we report the first out-of-ecliptic remote-sensing observations of the south pole of the Sun from a high-latitude campaign of the Solar Orbiter spacecraft which reveal spatial and temporal evolution of supergranular convective cells. The supergranular cells have spatial scales of 10--40,Mm. From eight days of observations starting on 2025 March 16, our analysis shows that the magnetic network migrates poleward, on average, at high latitudes (above 60\textdegree), with speeds in the range of 10--20,m,s$^{-1}$, depending on the structures being tracked. These results shed light on the buildup of the polar magnetic field that is central to our understanding of the solar cycle and the heliospheric magnetic field.

The (\alpha) effect is believed to play a key role in the generation of the solar magnetic field. A fundamental test for its significance in the solar dynamo is to look for magnetic helicity of opposite signs in the two hemispheres, and at small and large scales. However, measuring magnetic helicity is compromised by the inability to fully infer the magnetic field vector from observations of solar spectra, caused by what is known as the (\pi) ambiguity of spectropolarimetric 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 Fourier spectra of B and parity-even quantities such as E or temperature T are a robust proxy for magnetic helicity of solar magnetic fields. We analyse polarisation measurements of active regions observed by the Helioseismic and Magnetic Imager on board the Solar Dynamics observatory. Theory predicts the 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 of their sign based on the hemisphere of the active regions. We find that: (i) EB and TB correlations are a reliable proxy for magnetic helicity, when computed from linear polarisation measurements away from spectral line cores, and (ii) E polarisation reverses its sign close to the line core. Our analysis reveals Faraday rotation to not have a significant influence on the computed parity-odd correlations. The EB decomposition of linear polarisation appears to be a good proxy for magnetic helicity independent of the (\pi) ambiguity. This allows us to routinely infer magnetic helicity directly from polarisation measurements. The full article can be found at https://arxiv.org/abs/2001.10884

The (\alpha) effect is believed to play a key role in the generation of the solar magnetic field. A fundamental test for its significance in the solar dynamo is to look for magnetic helicity of opposite signs in the two hemispheres, and at small and large scales. However, measuring magnetic helicity is compromised by the inability to fully infer the magnetic field vector from observations of solar spectra, caused by what is known as the (\pi) ambiguity of spectropolarimetric 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 Fourier spectra of B and parity-even quantities such as E or temperature T are a robust proxy for magnetic helicity of solar magnetic fields. We analyse polarisation measurements of active regions observed by the Helioseismic and Magnetic Imager on board the Solar Dynamics observatory. Theory predicts the 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 of their sign based on the hemisphere of the active regions. We find that: (i) EB and TB correlations are a reliable proxy for magnetic helicity, when computed from linear polarisation measurements away from spectral line cores, and (ii) E polarisation reverses its sign close to the line core. Our analysis reveals Faraday rotation to not have a significant influence on the computed parity-odd correlations. The EB decomposition of linear polarisation appears to be a good proxy for magnetic helicity independent of the (\pi) ambiguity. This allows us to routinely infer magnetic helicity directly from polarisation measurements. The full article can be found at https://arxiv.org/abs/2001.10884