Magnetic Activity in the Galactic Centre Region -- Fast Downflows along
  Rising Magnetic Loops
  We studied roles of the magnetic field on the gas dynamics in the Galactic
bulge by a three-dimensional global magnetohydrodynamical simulation data,
particularly focusing on vertical flows that are ubiquitously excited by
magnetic activity. In local regions where the magnetic filed is stronger, it is
frequently seen that fast down-flows slide along inclined magnetic field lines
that are associated with buoyantly rising magnetic loops. The vertical velocity
of these down-flows reaches ~ 100 km s$^{-1}$ near the foot-point of the loops
by the gravitational acceleration toward the Galactic plane. The two footpoints
of rising magnetic loops are generally located at different radial locations
and the field lines are deformed by the differential rotation. The angular
momentum is transported along the field lines, and the radial force balance
breaks down. As a result, a fast downflow is often observed only at the one
footpoint located at the inner radial position. The fast downflow compresses
the gas to form a dense region near the footpoint, which will be important in
star formation afterward. Furthermore, the horizontal components of the
velocity are also fast near the foot-point because the down-flow is accelerated
along the magnetic sliding slope. As a result, the high-velocity flow creates
various characteristic features in a simulated position-velocity diagram,
depending on the viewing angle.
