The magnetic fine structure of the Sun’s polar region as revealed by Sunrise

Abstract

Context. Polar magnetic fields play a key role in the solar magnetic cycle and they are the source of a significant portion of the interplanetary magnetic field. However, observations of the poles are challenging and hence our understanding of the polar magnetic environment is incomplete. Aims. We deduce properties of small-scale magnetic features in the polar region using high-resolution data and specifically aim to determine the flux per patch above which one magnetic polarity starts to dominate over the other. Methods. We study the high spatial resolution, seeing-free observations of the north solar polar region, obtained with the IMaX instrument on-board the balloon-borne Sunrise observatory during June 2009, at the solar activity minimum. We performed inversions of the full Stokes vector recorded by IMaX to retrieve atmospheric parameters of the Sun's polar region, mainly the temperature stratification and the magnetic field vector. Results. We infer kilo-Gauss (kG) magnetic fields in patches harbouring polar faculae, without resorting to a magnetic filling factor. Within these patches we find the maxima of the magnetic field to be near the dark narrow lanes, which are shifted towards the disc centre side in comparison to the maxima in continuum intensity. In contrast, we did not find any fields parallel to the solar surface with kG strengths. In addition to the kG patches, we found the polar region to be covered in patches of both polarities, which have a range of sizes. We find the field strength of these patches to increase with increasing size and flux, with the smaller patches showing a significant dispersion in field strength. The dominating polarity of the north pole during this phase of the solar cycle is found to be maintained by the larger patches with fluxes above 2.3 × 10 17 Mx.

A Parametric Study of Performance of Two Solar Wind Velocity Forecasting Models During 2006–2011

“…2. The input magnetograms to the models are unreliable near the polar regions (Hoeksema et al, 2006;Prabhu et al, 2020). 3.…”

“…For a better interpretation, it may be important to highlight the following points about our framework The HUX model extrapolates SW velocities under a steady state assumption (Riley et al., 2015). The input magnetograms to the models are unreliable near the polar regions (Hoeksema et al., 2006; Prabhu et al., 2020). The steady state models used in this framework are limited in the sense that they can not be used to replicate CMEs as shown in Figure 3.…”

Dynamics of Photospheric Magnetic Flux Distribution and Variations in Solar RVs: A Study Using HARPS-N Solar and SDO Observations

“…Regarding the use of a flux limit to separate the IN and NE fields, although high-resolution observations broadly agree on such a value (∼3 × 10 17 Mx) (Gošić et al 2014;Prabhu et al 2020), we note that it is not a strict limit as these fields have significantly broad distributions with observed peak fluxes dependent on the resolution of observations (Zhou et al 2013) and hence it is always possible that there exist kilogauss NE elements with a slightly smaller flux and vice versa for IN elements because intermediate states of splitting and merging are a common occurrence in the dynamics of NE (Schrijver et al 1997) and IN (Campbell et al 2021) fields.…”

“…Such an organization of small-scale magnetic flux also has a sound theoretical basis, which derives from the effects of radiative smoothing on the convective collapse mechanism (Venkatakrishnan 1986;Rajaguru & Hasan 2000). Recent very highresolution and high polarimetric sensitivity observations (Gošić et al 2014;Prabhu et al 2020;Campbell et al 2021) confirm the above basic characteristics of NE and IN magnetic fields in the solar photosphere, and also give a resolved picture of a typical weak IN field: it is a low-lying small loop with its highly inclined (linear polarization causing) segment, over a granule, flanked by vertical (circular polarization causing) field within intergranular lane. A typical NE field element is a vertical structure rooted in the supergranular boundary and extending high into the chromospheric layers.…”

Solar Irradiance Variability Monitor for the Galileo Solar Space Telescope Mission: Concept and Challenges

“…The observations of Hinode's spectropolarimeter revealed horizontal magnetic flux estimated by the Zeeman effect [37]. Studying the magnetic structure differences in quiet Sun in Polar regions and low latitudes is more challenging using data from the ecliptic plane [38].…”