The Sun 91
FIGURE 19 2D numerical MHD simulation of a solar flare with chromospheric evaporation and
anisotropic heat conduction in the framework of a 2D magnetic reconnecting geometry. The
temporal evolution of the plasma temperature (top row) and density (bottom row) is shown. The
temperature and density scale is shown in the bars on the right side. The simulation illustrates the
propagation of thermal conduction fronts and the upflows of chromospheric plasma in response.
(Courtesy of Takaaki Yokoyama and Kazunari Shibata.)
velocities caused by perpendicular forces (i.e., E×B-
drifts), and gyromotion caused by the Lorentz force of the
magnetic field. Theoretical models of particle acceleration
in solar flares can be broken down into three groups: (1) DC
electric field acceleration, (2) stochastic or second-order
Fermi acceleration, and (3) shock acceleration. In the mod-
els of the first group, there is a paradigm shift from large-
scale DC electric fields (of the size of flare loops) to small-
scale electric fields (of the size of magnetic islands produced
by the tearing mode instability). The acceleration and tra-
jectories of particles is studied more realistically in the inho-
mogeneous and time-varying electromagnetic fields around
magnetic X-points and O-points of magnetic reconnec-
tion sites, rather than in static, homogeneous, large-scale