Coronal Magnetic Field Topology From Total Solar Eclipse Observations

Measuring the global magnetic field of the solar corona remains exceptionally challenging. The fine-scale density structures observed in white-light images taken during total solar eclipses are currently the best proxies for inferring the magnetic field direction in the corona from the solar limb out to several solar radii (R). We present, for the first time, the topology of the coronal magnetic field continuously between 1 and 6 R, as quantitatively inferred with the rolling Hough transform for 14 unique eclipse coronae that span almost two complete solar cycles. We find that the direction of the coronal magnetic field does not become radial until at least 3 R, with a high variance between 1.5 and 3 R at different latitudes and phases of the solar cycle. We find that the most nonradial coronal field topologies occur above regions with weaker magnetic field strengths in the photosphere, while stronger photospheric fields are associated with highly radial field lines in the corona. In addition, we find an abundance of field lines that extend continuously from the solar surface out to several solar radii at all latitudes, regardless of the presence of coronal holes. These results have implications for testing and constraining coronal magnetic field models, and for linking in situ solar wind measurements to their sources at the Sun.