Evaluating the Morphology of the Local Interstellar Medium: Using New
  Data to Distinguish Between Multiple Discrete Clouds and a Continuous Medium
  Ultraviolet and optical spectra of interstellar gas along the lines of sight
to nearby stars have been interpreted by Redfield & Linsky (2008) and previous
studies as a set of discrete warm, partially ionized clouds each with a
different flow vector, temperature, and metal depletion. Recently, Gry &
Jenkins (2014) have proposed a fundamentally different model consisting of a
single cloud with nonrigid flows filling space out to 9 parsecs from the Sun
that they propose better describes the local ISM. Here we test these
fundamentally different morphological models against the spatially unbiased
Malamut et al. (2014) spectroscopic data set, and find that the multiple cloud
morphology model provides a better fit to both the new and old data sets. The
detection of three or more velocity components along the lines of sight to many
nearby stars, the presence of nearby scattering screens, the observed thin
elongated structures of warm interstellar gas, and the likely presence of
strong interstellar magnetic fields also support the multiple cloud model. The
detection and identification of intercloud gas and the measurement of neutral
hydrogen density in clouds beyond the Local Interstellar Cloud could provide
future morphological tests.
