Interpretation of the coronal magnetic field configuration of the Sun

TL;DR

This study uses two models of the solar corona and solar wind to investigate the magnetic field configuration, challenging assumptions about the relationship between observed brightness and magnetic topology, and suggesting open magnetic fields are widespread.

Contribution

The paper introduces two Alfvénic-turbulence-based models of the solar corona, one with and one without closed magnetic regions, to interpret coronal magnetic field observations.

Findings

Polarized brightness observations are not reliable proxies for magnetic topology.

Ulysses data do not exclude widespread open magnetic fields on the Sun.

Both models fit observational data equally well.

Abstract

The origin of the heliospheric magnetic flux on the Sun, and hence the origin of the solar wind, is a topic of hot debate.While the prevailing view is that the solar wind originates from outside coronal streamer helmets, there also exists the suggestion that the open magnetic field spans a far wider region.Without the definitive measurement of the coronal magnetic field, it is difficult to resolve the conflict between the two scenarios without doubt.We present two 2-dimensional, Alfv\'enic-turbulence-based models of the solar corona and solar wind, one with and the other without a closed magnetic field region in the inner corona.The purpose of the latter model is to test whether it is possible to realize a picture suggested by polarimetric measurements of the corona using the FeXIII 10747\AA\ line, where open magnetic field lines seem to penetrate the streamer base.The boundary conditions at the coronal base are able to account for important observational constraints, especially those on the magnetic flux distribution.Interestingly, the two models provide similar polarized brightness (pB) distributions in the field of view (FOV) of SOHO/LASCO C2 and C3 coronagraphs.In particular, a dome-shaped feature is present in the C2 FOV even for the model without any closed magnetic field.Moreover, both models fit equally well the Ulysses data scaled to 1 AU.We suggest that: 1) The pB observations cannot be safely taken as a proxy for the magnetic field topology, as often implicitly assumed.2) The Ulysses measurements, especially the one showing a nearly uniform distribution with heliocentric latitude of the radial magnetic field, do not rule out the ubiquity of open magnetic fields on the Sun.