Magnetic Reconnection and Current Sheet in CME/Flare
Processes: Theories and Observations
 
Jun Lin

In the astrophysical environment, magnetic
reconnection is probably the unique way that can
quickly convert the magnetic energy into other types
of energy, such as thermal and kinetic energy. 
Because of the high electric conductivity of the
plasma in the astrophysical environment, such fast
energy conversion or dissipation is usually confined
in a very local region like the X-type neutral point
or the electric current sheet. In reality, the plasma
conductivity is fairly high, but it is not infinitely
high, so, the finite rate of dissipation in the
current sheet yields that any reconnection site with
finite scale is not able to exist long unless plasma
and anti-parallel magnetic fields can be somehow
continuously brought into the relevant region, such as
the long duration existence of the geomagnetic tail of
the Earth and the helmet streamer of the Sun are
supported by the sustained flow of the solar wind.
However, the current sheet structure that appears in
the CHSKP model of two-ribbon flares occurring in the
lower corona of the Sun can never exist for long in
the solar atmosphere, it has to be produced as the
closed field lines on the lower corona are stretched
outward by the eruption. The magnetic reconnection
occurring in such a current sheet plays an essential
role in helping CME smoothly propagate in the
outermost corona and interplanetary space, and in
creating growing flare loop system in the corona and
the separating flare ribbons on the solar disk. In
this report, we are going to overview the models of
the solar eruptions that manifest both CME and flare,
discuss the model that describes the detailed
development of a long current sheet, and the
corresponding observational consequences. Furthermore,
observations of the current sheet formed by the
eruptions will also be displayed and compared with the
theoretical results.