Molecular gas distribution perpendicular to the Galactic plane
  We use the ~370 square degrees data from the MWISP CO survey to study the
vertical distribution of the molecular clouds (MCs) toward the tangent points
in the region of l=[16,52]deg and |b|<5.1deg. The molecular disk consists of
two components with the layer thickness (FWHM) of ~85pc and ~280pc,
respectively. In the inner Galaxy, the molecular mass in the thin disk is
dominant, while the molecular mass traced by the discrete MCs with weak CO
emission in the thick disk is probably <10% of the whole molecular disk. For
the CO gas in the thick disk, we identified 1055 high-z MCs that are >100pc
from the Galactic plane. However, only a few samples (i.e., 32 MCs) are located
in the |z|>360pc region. Typically, the discrete MCs of the thick disk
population have a median peak temperature of 2.1 K, a median velocity
dispersion of 0.8km/s, and a median effective radius of 2.5pc. The median
surface density of these MCs is 6.8 Msun/pc^2, indicating very faint CO
emission for these high-z MCs. The cloud-cloud velocity dispersion is 4.9+-1.3
km/s and a linear variation with a slope of -0.4 km/s/kpc is obtained in the
region of R_GC=2.2-6.4kpc. Assuming that these clouds are supported by their
turbulent motions against the gravitational pull of the disk, a model of
rho0(R) = 1.28exp(-R/3.2kpc) Msun/pc^3 can be used to describe the distribution
of the total mass density in the Galactic midplane.
