  We present observations of probable line-of-sight acceleration of a broad
absorption trough of C IV in the quasar SDSS J024221.87+004912.6. We also
discuss how the velocity overlap of two other outflowing systems in the same
object constrains the properties of the outflows. The Si IV doublet in each
system has one unblended transition and one transition which overlaps with
absorption from the other system. The residual flux in the overlapping trough
is well fit by the product of the residual fluxes in the unblended troughs. For
these optically thick systems to yield such a result, at least one of them must
consist of individual subunits rather than being a single structure with
velocity-dependent coverage of the source. If these subunits are identical,
opaque, spherical clouds, we estimate the cloud radius to be r = 3.9 10^15 cm.
If they are identical, opaque, linear filaments, we estimate their width to be
w = 6.5 10^14 cm. These subunits are observed to cover the Mg II broad emission
line region of the quasar, at which distance from the black hole the above
filament width is equal to the predicted scale height of the outer atmosphere
of a thin accretion disk. Insofar as that scale height is a natural size scale
for structures originating in an accretion disk, these observations are
evidence that the accretion disk can be a source of quasar absorption systems.
Based on data from ESO program 075.B-0190(A).
