Magnetic reconnection can be studied in the extended solar corona according to the following two different approaches: first, by measuring the non-thermal broadening of coronal lines; secondly, by attempting to detect the emission from magnetic islands which are expected to develop within the current sheets above coronal streamers.
During reconnection, plasma entering the current
sheet with a drift velocity 
, is expected to be ejected sideways
with an outflow velocity V of the order of
the Alfvén velocity 
where 
is the density inside the current sheet, and M is the
plasma average molecular weight. Assume a non-neutral current sheet
with a transverse magnetic
field component, 
, added to the reconnecting component,
. If pressure equilibrium is established, the outflow velocity can be
expressed in terms of the temperature inside the current sheet, as
,
where 
The value assumed by the term f(
) depends on the electron to
ion temperature ratio 
, which is a function of the particular
conditions within the current sheet (Antonucci and Somov, 1992).
Therefore, magnetic reconnection in current sheets is expected
to give an observable symmetric broadening in spectral line profiles,
particularly relevant for heavy ions.
For example for a current sheet at T
= 9 10
K, we expect
non-thermal velocities within 10 - 10
km s
in the O VI, Mg X,
Si XII collisionally excited lines (Verneta et al. 1994, in preparation).
Therefore as an effect of magnetic reconnection
processes we expect
non-thermal broadenings in the UV spectral lines.
As an alternative possibility we can expect to detect magnetic reconnection
by observing the excitation of the tearing instability in the current sheet
forming in a coronal streamer. Within the current sheet we expect the
development of elongated magnetic islands with length 2 10
cm,
lifetime 
10 h and emission measure < 10
cm
, which
should be easily mesurable if they exist. The magnetic islands are also
expected to drift outward at 40 km s
at 4 
(Verneta at al.
1994, in press).
In order to investigate the role of magnetic reconnection through the observation of non-thermal broadening of the UV lines we propose to measure the line profiles of O VI, Mg X, Si XII in regions where the magnetic configuration inferred from the geometry of the corona is suspected to be appropriate to form a current sheet (Observation sequence: Coronal Observation 4).