The equatorial streamer observed by UVCS/SOHO above the west limb of
the Sun on May 4, 1996 in the radiation of the O VI ions at 103.2 nm. 
The curves sketched on the image represent a possible magnetic field
configuration  (see Noci et al. 1997, ESA SP-404, p. 75).

The open field lines allow the coronal plasma to flow out of the
streamer region.  However, because of the narrowing of the
cross-sections of the flow tubes, as the heliocentric distance
increases, the wind is slower than in coronal holes and the mechanism
which carries the oxygen ions in the wind less efficient. Hence oxygen
is depleted in the low brightness streamer core (see previous images).
At larger heliocentric distances, the wind from within the streamers
may remain slower than that originating from coronal holes
(fast wind), becoming the interplanetary slow wind.