96 Encyclopedia of the Solar System
FIGURE 23 Numerical MHD simulation of the evolution of a CME, driven by turbulent diffusion.
The four panels correspond to the times (a)t=850, (b)t=950, (c)t=1050, and (d)t=1150, where
viscous relaxation is started att=850, triggering a global disruption involving opening, reconnection
through the overlying arcade and below, and the formation of a current sheet, associated with a high
dissipation of magnetic energy and a strong increase of kinetic energy. (Courtesy of T. Amari.)instability of twisted structures (Fig. 23). The geometry of
CMEs is quite complex, exhibiting a variety of topolog-
ical shapes from spherical semishells to helical fluxropes
(Fig. 24), and the density and temperature structure of
CMEs is currently investigated with multiwavelength im-
agers. The height-time, velocity, and acceleration profiles of
CMEs seem to establish two different CME classes: gradual
CMEs associated with propagating interplanetary shocks
and impulsive CMEs caused by coronal flares. The total en-
ergy of CMEs (i.e., the sum of magnetic, kinetic, and gravi-
tational energy) seems to be conserved in some events, and
the total energy of CMEs is comparable to the energy range
estimated from flare signatures. A phenomenon closely as-
sociated with CMEs is coronal dimming (Fig. 13), which
is interpreted in terms of an evacuation of coronal mass
during the launch of a CME. The propagation of CMEs in
interplanetary space provides diagnostic information on the
heliospheric magnetic field, the solar wind, interplanetary
shocks, solar energetic particle (SEP) events, and interplan-
etary radio bursts.