This observing program aims to measure the effects of collisionless shocks
in the solar corona.
Several theoretical studies have shown that it might be possible
for standing and propagating shocks to form in the inner
corona, below 4 
,
as a result of impulses, or changes in the divergence
of the flow tubes (Habbal and Rosner 1984, Leer and Holzer 1990).
More recently Esser and Habbal (1990) have shown that these
shocks produce measurable changes in the Ly 
line intensity
and the polarization brightness.
It will be possible, but difficult, to measure the jump in
density, velocity, proton and ion temperatures across
a strong collisionless shock by measuring the
Ly
profile. Changes in the O VI and
other ion abundances will be related to 
.
The 
velocity distribution just behind
the shock will be a mixture of pre-shock and post-shock
velocity distributions, corresponding to neutrals
which have or have not undergone charge transfer with
post-shock ions.
It may be possible to see
the effects of the shock precursor as well. This
will be useful for studies of non-thermal
particle acceleration in shocks, electron-ion temperature
equilibration, and the energetics of CMEs.
When studying shocks, the difficulties are their
unpredictability, their short duration,
and the time lag for the neutral H distribution
to respond to changes in the proton distribution.
A fast (1000 km/s) shock will cross the UVCS slit
in about 12 seconds (for a 0.05 mm slit). The precursor
is likely to be in the slit for only
about 10-20 seconds as well. The charge transfer time
is about 
seconds. During that time the
neutral population at any position includes two populations;
one with the pre-shock ion distribution and one with the
post-shock ion velocity and temperature. If we catch an
event in the quiet corona at 1.5 
, the pre-shock
density is around 
, and the charge transfer
relaxation time is 
seconds. The electron temperature
will probably increase by a modest amount at the shock, then
slowly (
seconds) approach the post-shock ion temperature.
The electron-ion equilibration is one of the major uncertainties
in the physics of strong collisionless shocks.
On the equilibration timescale,
the increased electron temperature will reduce the 
and O VI
concentrations and increase Si XII. The count rates in all lines
will be complicated functions of time which reflect the shock
compression, the increasing electron temperature, and the large bulk and thermal velocities
of the ions which affect the Doppler dimming. The estimates in the tables pertain to a 700
km/s shock at 1.5 
, but they are extremely uncertain.
Because these events are unpredictable, much of this analysis may be done on data serendipitously taken. We will want to have very wide spectral coverage to look for low ionization material driving the shock. The observing program relative to CME's might be adequate for this purpose.
For studies of standing and propagating shocks in general in the corona,
observations can be made between 1.5 and 4 
,
in spatial steps of 0.1 
. The dwell time could be
1 min below 2 
, and increase to 5 min at larger
distances. Such an observing sequence should be repeated
for different azimuthal directions within a coronal hole,
or a quiet region.
Ideally it would be best to coordinate this observing plan
with LASCO.
The first column refers to a 700 km/s shock at 1.5 
, but the
predicted intensities are extremely uncertain.
For the operational mode in this case we refer to the CME's JOP.
The second column is conceived to observe in general the shock phenomenon.
Physics of Shock Waves
