On 18 April 2000, several instruments on SOHO observed a coronal 
mass ejection (CME) associated with the eruption of a long 
filament in the southern hemisphere.   This image shows the
first five moments of the H I Lyman alpha line profile.
From top to bottom: the zeroth moment is the total line intensity;
the first moment is the net Doppler shift of the profile; the
second moment corresponds to the line width; the third moment
indicates the net "skewness" of the profile; and the fourth moment 
indicates the "kurtosis," or departure in its symmetric component
from a Gaussian shape.

The UVCS data show that the different threads have different
Doppler velocities and move with different speeds along the
UVCS slit.  The Doppler velocities appear to be correlated with
position along the slit (blue shift increases to the northwest),
suggesting some kind of rotational motion of the threads around
each other.  This may be due to untwisting of magnetic field
lines in the legs of the CME.  Such measurements provide
a method for determining the sign of magnetic helicity in
erupting filaments:  left-helical fields which unwind but are
anchored at the solar surface are predicted to have clockwise
rotation in the corona (as seen from the Sun), while right-helical
fields are predicted to have counter-clockwise rotation.
Therefore, the observed rotation provides information about the
3D structure and helicity of the coronal magnetic field.
Such measurements may shed light on the origin of global helicity
patterns (Zirker et al. 1997, Solar Phys., 175, 27) and may
also be correlated with in-situ measurements of "magnetic clouds"
in interplanetary space.