Interchange Reconnection and Slow Solar Wind Formation at the boundaries of open field regions in the Solar Corona

Abstract:

Interchange reconnection, i.e., magnetic reconnection
at the interface between open and closed corona, is
thought to contribute to the formation of the slow
solar wind, since it can inject the hotter and denser
plasma from closed regions into the heliosphere,
and account for the different slow wind composition (that
is similar to the plasma of closed regions) respect
to the fast wind.

The interchange process has mostly been investigated
for magnetic field lines with opposite polarity and null points,
either for the case of counterdirected loops
(e.g., Fisk et al. 1999, Fisk and Schwadron 2001), or in
correspondence of null points at the apex of streamers or
pseudo-streamers (e.g., Wang et al. 1998,
Edmondson et al. 2010, Del Zanna et al. 2011).
Magnetic reconnection can certainly occur in these configurations,
but they occupy a very small volume of the corona.

On the other hand component magnetic reconnection at the boundary
between coronal holes and streamers or pseudo-streamers has
received less attention, even though it can occur around
the entire extension of such boundaries.

Magnetic reconnection is at the basis of Parker's
nanoflare scenario for the heating of coronal loops.
Modeling such regions in cartesian geometry with a strong
guide field, it has been shown numerically that photospheric
motions induce a magnetic field
component orthogonal to the strong axial field characterized
by the presence of many current sheets, where the field lines
are locally oppositely directed, and can reconnect
(Einaudi et al. 1996; Dmitruk and Gomez 1997).
The reconnection of the orthogonal component of the magnetic
field leads to a change of connectivity of the field lines
of the total magnetic field that connect one photospheric boundary
to the other.

We have shown that a similar interchange mechanism
can operate in and around the boundaries between open and closed
regions inducing a continual stochastic rearrangement of connectivity
everywhere along the open-closed boundary (Rappazzo et al. 2012).

We examine a reduced MHD model of a simplified interface
region between open and closed corona. We extend previous
results to quantify the flux of mass density,
heat and momentum from the closed to the adjacent open region
through their shared boundary, and model the impact of this flux
on the acceleration of the slow component of the solar wind.