Gyrokinetic electron acceleration in the force-free corona with anomalous resistivity

Abstract

We numerically explore electron acceleration and coronal heating by dissipative electric fields. Electrons are traced in linear force-free magnetic fields extrapolated from SOHO/MDI magnetograms, endowed with anomalous resistivity ($\eta$) in localized dissipation regions where the magnetic twist $\nabla \times \bhat$ exceeds a given threshold. Associated with $\eta >0$ is a parallel electric field $\mathbf{E}=\eta \mathbf{j}$ which can accelerate runaway electrons. In order to gain observational predictions we inject electrons inside the dissipation regions and follow them for several seconds in real time. Precipitating electrons which leave the simulation system at height $z$ = 0 are associated with hard X rays, and electrons which escape at height $z$ $\sim$ 3$\cdot 10^4$ km are associated with normal-drifting type IIIs at the local plasma frequency. A third, trapped, population is related to gyrosynchrotron emission. Time profiles and spectra of all three emissions are calculated, and their dependence on the geometric model parameters and on $\eta$ is explored. It is found that precipitation generally preceeds escape by fractions of a second, and that the electrons perform many visits to the dissipation regions before leaving the simulation system. The electrons impacting $z$ = 0 reach higher energies than the escaping ones, and non-Maxwellian tails are observed at energies above the largest potential drop across a single dissipation region. Impact maps at $z$ = 0 show a tendency of the electrons to arrive at the borders of sunspots of one polarity. Although the magnetograms used here belong to non-flaring times, so that the simulations refer to nanoflares and `quiescent' coronal heating, it is conjectured that the same process, on a larger scale, is responsible for solar flares.

References in corpus (6)

• The spectral evolution of impulsive solar X-ray flares
• Survey on solar X-ray flares and associated coherent radio emissions
• Particle Acceleration in Multiple Dissipation Regions
• The Effect of Coherent Structures on Stochastic Acceleration in MHD Turbulence
• Temporal Correlation of Hard X-rays and Meter/Decimeter Radio Structures in Solar Flares
• Spatial Evidence for Transition Radiation in a Solar Radio Burst

Cited by in corpus (5)

• Magnetic Field Extrapolations in the Corona: Success and Future Improvements
• 3D Solar Null Point Reconnection MHD Simulations
• Particle acceleration at a reconnecting magnetic separator
• Numerical Simulation of Superhalo Electrons Generated by Magnetic Reconnection in the Solar Wind Source Region
• Astrophysics in 2006