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.

References in corpus (2)

• Sympathetic Magnetic Breakout Coronal Mass Ejections from Pseudostreamers
• Coronal cavities: observations and implications for the magnetic environment of prominences

Cited by in corpus (7)

• Origins of the Ambient Solar Wind: Implications for Space Weather
• Coronal Magnetic Field Topology From Total Solar Eclipse Observations
• Spectropolarimetric Insight into Plasma-Sheet Dynamics of a Solar Flare
• Data-Optimized Coronal Field Model: I. Proof of Concept
• Successive occurrences of quasi-circular ribbon flares in a fan-spine-like configuration involving hyperbolic flux tube
• Spectropolarimeter on-board the Aditya-L1: Polarization Modulation and Demodulation
• Compensating Faraday depolarization by magnetic helicity in the solar corona