88 Encyclopedia of the Solar System
FIGURE 15 (Continued)FIGURE 16 Erupting filament observed withTRACEat 171A ̊
on July 19, 2000, 23:30 UT, in Active Region 9077. The dark
filament mass has temperatures around 20,000 K, while the hot
kernels and threads contain plasma with temperatures of 1.0 MK
or hotter. The erupting structure extends over a height of 75,000
km here. (Courtesy ofTRACEand NASA.)
The best known flare/CME models entail magnetic re-
connection processes that are driven by a rising filament/
prominence, flux emergence, converging flows, or shear
motion along the neutral line. Flare scenarios with a driver
perpendicular to the neutral line (rising prominence, flux
emergence, convergence flows) are formulated as 2D re-
connection models, while scenarios that involve shear along
the neutral line (tearing-mode instability, quadrupolar flux
transfer, the magnetic breakout model, sheared arcade in-
teractions) require 3D descriptions. A 2D reconnection
model involving a magnetic X-point is shown in Fig. 17
(left); a generalized 3D version involving a highly sheared
neutral line is sketched in Fig. 17 (right). There are more
complex versions like the magnetic breakout model, where
a second arcade triggers reconnection above a primary
arcade. Observational evidence for magnetic reconnec-
tion in flares includes the 3D geometry, reconnection in-
flows, outflows, detection of shocks, jets, ejected plasmoids,
and secondary effects like particle acceleration, conduction
fronts, and chromospheric evaporation processes. Flare im-
ages in soft X-rays often show the cusp-shaped geometry of