Magnetic nulls and super-radial expansion in the solar corona
Gibson, S. E., Dalmasse, K., Rachmeler, L. A., De Rosa, M. L., Tomczyk, S., De Toma, G., … Galloy, M. (2017). Magnetic nulls and super-radial expansion in the solar corona. The Astrophysical Journal, 840, L13. doi:10.3847/2041-8213/aa6fac
Magnetic fields in the Sun's outer atmosphere—the corona—control both solar-wind acceleration and the dynamics of solar eruptions. We present the first clear observational evidence of coronal magnetic nulls in off-limb linearly polarized observations of pseudostreamers, taken by the Coronal Multi... Show moreMagnetic fields in the Sun's outer atmosphere—the corona—control both solar-wind acceleration and the dynamics of solar eruptions. We present the first clear observational evidence of coronal magnetic nulls in off-limb linearly polarized observations of pseudostreamers, taken by the Coronal Multichannel Polarimeter (CoMP) telescope. These nulls represent regions where magnetic reconnection is likely to act as a catalyst for solar activity. CoMP linear-polarization observations also provide an independent, coronal proxy for magnetic expansion into the solar wind, a quantity often used to parameterize and predict the solar wind speed at Earth. We introduce a new method for explicitly calculating expansion factors from CoMP coronal linear-polarization observations, which does not require photospheric extrapolations. We conclude that linearly polarized light is a powerful new diagnostic of critical coronal magnetic topologies and the expanding magnetic flux tubes that channel the solar wind. Show less