Magnetic Nulls and Super-radial Expansion in the Solar Corona
Abstract
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 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- May 2017
- DOI:
- 10.3847/2041-8213/aa6fac
- arXiv:
- arXiv:1704.07470
- Bibcode:
- 2017ApJ...840L..13G
- Keywords:
-
- solar wind;
- Sun: corona;
- Sun: magnetic fields;
- Astrophysics - Solar and Stellar Astrophysics
- E-Print:
- The Astrophysical Journal Letters, Volume 840, Issue 2, article id. L13, 6 pp. (2017)