David Pontin, Univ of Newcastle, Australia

"The Parker Problem”: Heating the Sun’s corona by magnetic field line braiding 

One of the leading mechanisms for explaining the high temperature of the Sun’s corona is Parker’s topological dissipation mechanism. It is based on the hypothesis that if an equilibrium magnetic field is subjected to an arbitrary, small perturbation, then - under ideal plasma dynamics - the resulting magnetic field will in general not relax towards a smooth equilibrium, but rather towards a state containing tangential magnetic field discontinuities. Then, even at astrophysical plasma parameters, as the singular state is approached dissipation must eventually become important, leading to the onset of rapid magnetic reconnection and energy dissipation. This topological dissipation mechanism remains a matter of debate, and is a key ingredient in the nanoflare model for coronal heating. We review various theoretical and computational approaches that have sought to prove or disprove Parker’s hypothesis, in the context of coronal heating, and discuss different approaches that have been taken to investigating whether braiding of magnetic field lines is responsible for maintaining the observed coronal temperatures. We discuss the many advances that have been made, and highlight outstanding open questions.

Date and time: 
Wednesday, April 28, 2021 - 3:00pm to 4:00pm