Contributed Talk - Splinter Solar

Wednesday, 23 September 2020, 10:23   (virtual room L)

MHD avalanches: coronal heating in braided fields

Jack Reid, Alan W. Hood, Clare E. Parnell, Peter J. Cargill
University of St Andrews

Parker's 'nanoflare' model addresses the coronal heating problem by proposing heating via the cumulative action of many dissipative events, releasing magnetic energy through reconnection. Assessing the viability of dissipative heating in braided magnetic fields, we focus upon an MHD 'avalanche': a succession of recurring events, which is caused as a single, microscopic instability disrupts, and propagates through, braided, but stable, flux tubes. Three-dimensional MHD simulations are used to model the formation, stressing, and resultant instability of a multi-stranded coronal loop, in order to determine and analyse the heating. An impulsive, localized, and 'bursty' heating, above a steady background, results: events are dispersed, and arise in a spectrum of sizes and magnitudes. Scaling of heating and energy flux with driving speed are evaluated. Field-aligned heating profiles inform heating functions injected into one-dimensional, thermodynamic models. The capacity of a braided magnetic field to convert injected Poynting flux into thermal energy is verified, found efficient, and demonstrated to maintain realistic coronal temperatures and densities.