As a key to understanding the basic mechanism
for fast reconnection in solar flares,
are proposed and examined.
We first briefly summarize recent solar observations
that give us hints on the role of plasmoid
(flux rope) ejections
in flare energy release.
We then discuss the plasmoid-induced-reconnection model,
which is an extention of the classical two-ribbon-flare
model which we refer to as the CSHKP model.
An essential ingredient of the new model is the
formation and ejection of a plasmoid which play
an essential role in the storage of magnetic
energy (by inhibiting
reconnection) and the induction of a strong inflow into reconnection region.
Using a simple analytical model, we show
that the plasmoid ejection and acceleration are closely
coupled with the reconnection process, leading to a
nonlinear instability for the
whole dynamics that determines the macroscopic
reconnection rate uniquely.
Next we show that
the current sheet tends to have a fractal
structure via the following process path:
tearing Rightarrow sheet thinning
Rightarrow Sweet-Parker sheet
Rightarrow secondary tearing
Rightarrow further sheet thinning
These processes occur repeatedly at smaller scales
until a microscopic
plasma scale (either the ion Larmor radius or the ion inertial length)
is reached where anomalous resistivity or
collisionless reconnection can occur.
The current sheet eventually
has a fractal structure with many plasmoids
(magnetic islands) of different sizes.
When these plasmoids are ejected out of the current
sheets, fast reconnection
occurs at various different scales
in a highly time dependent manner.
Finally, a scenario is presented for fast reconnection
in the solar corona on the basis of above
plasmoid-induced-reconnection in a fractal current sheet.
Authors: Kazunari Shibata and Syuniti Tanuma
Publication Status: Earth, Planets and Space, in press
Last Modified: 2001-01-04 01:11