Acceleration of the quasi-steady, high speed solar wind emanating from large coronal holes requires energy addition in th esupersonic region of the flow. It has been shown theoretically that Alfven waves from the sun can accelerate the solar wind to these high speeds. Until now this is the only mechanism that has been shown to enhance the flow speed of basically thermally driven solar wind to the high flow speeds observed in interplanetary space. The Alfven speed in the corona is quite large, so Alfven waves can carry a significant energy flux even for a small wave energy density. These waves can therefore propagate through the corona and inner solar wind, without increasing the solar wind mass flux substantially, and deposit their energy flux to the supersonic flow. For this mechanism to work the wave velocity amplitude in the inner corona must be 20-30 km/s. In the corona and inner solar wind region, where the flow speed is much smaller than the Alfven speed, both the solar wind flow and the wave energy transport are along the magnetic field. In this region the wave energy flux, F, in a magnetic flux tube is approximately constant,
where 
is the mass density, 
is the wave
velocity amplitude, 
is the Alfven
speed, and A is the cross-section of the flow tube. The magnetic flux,
, is constant so we have that the wave velocity amplitude
changes with density as
Here, the symbol "{}" indicates an ``average" value and the subscript ''0" indicates a reference level in the inner corona.
Heavy ions follow the electrons and protons in their motion in the wave,
and the width of the spectral line from such an ion should therefore
increase with the decreasing mass density, (i.e. increasing distance from
the Sun) if the wave broadening is larger than the thermal broadening.
As the wave velocity amplitude in the very inner corona must be 20-30
km/s a broadening of spectral lines from elements like O, Si, Mg, and
Fe, increasing with radial distance in the inner corona, should be seen
if MHD waves from the sun play an important role in accelerating high
speed streams from this region. There should be no significant damping
of Alfven waves inside 10-20 
and the wave velocity amplitude should
become larger than the thermal speed of the solar wind protons outside
4 
or so. In this region the neutral hydrogen atoms are coupled
to the protons by charge-exchange and ionization and recombination
processes. The time for these processes is short enough for the neutrals
to follow the electron-proton gas in the outflow from the Sun, but the
neutrals do not follow in the wave motion unless the frequency of the wave
is very small. For waves in such a frequency range that they propagate
as WKB-waves the neutrals do not follow in the wave motion, but the
interaction with protons is fast enough to produce a neutral hydrogen
velocity distribution with a ``temperature" perpendicular to the
magnetic field that is determined by the local wave velocity amplitude.
For the wave amplitudes necessary to accelerate high speed streams
the width of the 121.6 nm line from 
should increase from
4-5 
.
Observations of the width of the 121.6 nm line as a function of radial
distance should be carried out in large coronal holes beyond 4 
to see if the line width increases. It should be pointed out that
the intensity of the line may be quite small in the supersonic region
of the solar wind flow, but the density scale height is large and so
is the scale height for the width of the 121.6 nm line. Hence, there
is no need for good spatial resolution when these observations are carried
out.
In the figures below we show the FWHM and the intensity of the 121.6 nm
line versus closest distance of the line of sight, 
, in a spherically
symmetric two-fluid solar wind model. The parameters at the coronal base
are 
, 
K,
and 
= 1.85 Gauss. The results are for a monochromatic Alfven wave
with a frequency of 
, and the wave velocity amplitude
at the coronal base, 
, is 10, 20 and 30 km/s.
Observing Sequence: Coronal Observation 5