Turbulent relaxation of magnetic fields: 2. Self‐ organization and intermittency

Abstract

The intermittent nature of the stochastic MHD reconnection model of magnetic fields presented by Tetreault (this issue) is developed. It is shown that the large‐scale magnetic field topology relaxes in spatially localized regions or “domains”. This occurs where the magnetic fluctuations, initially generated nonlinearly in the form of field line bundles, self‐organize into coherent structures. The self‐organization is driven by the tendency for parallel currents flowing along field lines within a bundle to attract each other. The self‐organized structures take the form of flux tubes or ropes which in cross section are localized, topologically closed, magnetic island structures. The emergence of the structures out of the underlying MHD turbulence is an intermittent, macroscopic signature of the reconnection process and of a phase transition in the magnetic field topology. The structures are derived from a coarse‐grained variational principle satisfying the dynamical invariants of MHD, and as such, their emergence can be expected to occur in a wide variety of magnetic field topologies. The model may have geophysical and astrophysical application, including reconnection and associated flux transfer events (FTEs) in the Earth's dayside magnetopause, as well as flux emergence and the occurrence of solar flares on the Sun. Quantitative comparison (spatial scales, speeds, time scales, thresholds, intermittency, and spatial distribution) with satellite data of magnetopause FTEs is favorable.