  We present a detailed analysis of narrow of NaI and KI absorption resonance
lines toward nearly 40 T Tauri stars in Taurus with the goal of clarifying
their origin. The NaI 5889.95 angstrom line is detected toward all but one
source, while the weaker KI 7698.96 angstrom line in about two thirds of the
sample. The similarity in their peak centroids and the significant positive
correlation between their equivalent widths demonstrate that these transitions
trace the same atomic gas. The absorption lines are present towards both disk
and diskless young stellar objects, which excludes cold gas within the
circumstellar disk as the absorbing material. A comparison of NaI and CO
detections and peak centroids demonstrates that the atomic and molecular gas
are not co-located, the atomic gas is more extended than the molecular gas. The
width of the atomic lines corroborates this finding and points to atomic gas
about an order of magnitude warmer than the molecular gas. The distribution of
NaI radial velocities shows a clear spatial gradient along the length of the
Taurus molecular cloud filaments. This suggests that absorption is associated
with the Taurus molecular cloud. Assuming the gradient is due to cloud
rotation, the rotation of the atomic gas is consistent with differential
galactic rotation while the rotation of the molecular gas, although with the
same rotation axis, is retrograde. Our analysis shows that narrow NaI and KI
absorption resonance lines are useful tracers of the atomic envelope of
molecular clouds. In line with recent findings from giant molecular clouds, our
results demonstrate that the velocity fields of the atomic and molecular gas
are misaligned. The angular momentum of a molecular cloud is not simply
inherited from the rotating Galactic disk from which it formed but may be
redistributed by cloud-cloud interactions.
