SSP seminar

Magnetic islands due to reconnection: a new approach for modeling at global scales

Raymond Fermo (University of Maryland)

Monday 28th February 2011, 12:00 noon
Pratt conference room, 60 Garden Street

Magnetic reconnection is an important phenomenon in many space and astrophysical plasmas. Changes in magnetic topology can enable particle energization, flux transfer, and transport in such varied systems as solar and stellar coronae, planetary magnetospheres, and accretion disks. Simulations and observations of reconnection have shown that current sheets do not form a single x-line, but rather break up into many magnetic islands. These islands convect outwards, grow, and merge with one another. Neither global nor kinetic simulations can thoroughly explore the dynamics of these islands with sufficient separation of scales, especially for very large current sheets such as those in solar flares. We propose a statistical model for these magnetic islands which characterizes these islands by their flux and cross-sectional area. An evolution equation for the distribution function of islands is derived, whose steady-state solution underlies the important role that merging plays in island growth. Hall MHD simulations of long current layers show general agreement with the behavior predicted by this model. A database of 1098 magnetic islands observed by Cluster at the Earth's magnetopause is consistent with the model predictions. Applications for supra-arcade down-flowing structures in solar flares are also considered.


Section Photo