Flux-freezing Breakdown Observed in High-Conductivity Magnetohydrodyanamic Turbulence

Cristian Lalescu, Applied Math and Statistics


Alfven’s principle of “frozen-in” magnetic field lines for ideal plasmas explains diverse astrophysical phenomena, e.g. how proto-stars shed excess angular momentum. But frozen-in lines also preclude rapid changes in magnetic topology observed at high conductivities, e.g. in solar flares. Microphysical processes at scales below the ion gyroradius are a proposed explanation but it is unclear how these lead to rapid reconnection of astrophysical flux structures very much larger. We propose instead that turbulent Richardson advection brings field-lines implosively together to gyroradius separations from distances far apart. Here we report analysis of a simulation of MHD turbulence at high-conductivity that exhibits Richardson dispersion.

This effect of advection by rough velocities leads to line-motions that are completely indeterministic or “spontaneously stochastic”, as predicted in analytical studies. The turbulent breakdown of standard flux-freezing at scales greater than the ion gyroradius can explain fast reconnection of very large-scale flux structures, e.g. post-CME side-lobe magnetic fields reconnecting to an arcade of flare loops. The thick current sheet observed between flare arcade and CME is explained quantitatively by the stochastic flux-freezing due to turbulence.