Contracting magnetic islands in MHD simulations of flare reconnection
Abstract
The mechanisms that accelerate ionized particles to the energies required to produce the observed high-energy emission in solar flares are not well understood. Drake et al. (2006) proposed a kinetic mechanism for accelerating electrons in contracting magnetic islands formed by reconnection. In this model, particles that gyrate around magnetic field lines transit from island to island, increasing their energy by Fermi acceleration in those islands that are contracting. Macroscopic regions filled with a large number of these small islands are required to achieve the large observed rates of energetic electron production in flares, but at the moment it is impossible to simulate sufficiently large-scale systems using kinetic models. Our recent high-resolution, compressible MHD simulations of a breakout eruptive flare (Karpen et al. 2012) allow us to resolve in detail the generation and evolution of macroscopic magnetic islands in the flare current sheet, and to study the Drake et al. mechanism in a configuration that more closely represents the flare atmosphere and structure. Based on the Drake et al. studies, we attempt to close the gap between kinetic and fluid models by characterizing island contractions in our simulations as the islands move away from the main reconnection site toward the flare arcade. To that end, with our null-tracking capabilities, we follow the creation and evolution of X- and O-type (island) nulls that result from spatially and temporally localized reconnection. Preliminary results show that the initial energy of particles could be increased by 2-4 times in a typical contracting island, before the island reconnects with the underlying arcade. We conclude that this mechanism is a promising candidate for electron acceleration in flares, but further research is needed to extend our results to 3D flare conditions.
- Publication:
-
Solar Heliospheric and INterplanetary Environment (SHINE 2014)
- Pub Date:
- June 2014
- Bibcode:
- 2014shin.confE..37G