Where Does the Disk Turn Into the Halo? Cool H I in the Outer Milky Way
  Disk
  Using H I absorption spectra taken from the recent surveys of 21-cm line and
continuum emission in the Galactic plane, the distribution of cool atomic
clouds in the outer disk of the Milky Way is revealed. The warp of the midplane
is clearly seen in absorption, as it is in emission, and the cool, neutral
medium also shows flaring or increase in scale height with radius similar to
that of the warm atomic hydrogen. The mixture of phases, as measured by the
fraction of H I in the cool clouds relative to the total atomic hydrogen, stays
nearly constant from the solar circle out to about 25 kpc radius. Assuming cool
phase temperature ~50 K this indicates a mixing ratio of 15% to 20% cool H I,
with the rest warm.
