  A survey for the molecular clouds in the Galaxy with NANTEN mm telescope has
discovered molecular loops in the Galactic center region. The loops show
monotonic gradients of the line of sight velocity along the loops and the large
velocity dispersions towards their foot points. It is suggested that these
loops are explained in terms of the buoyant rise of magnetic loops due to the
Parker instability. We have carried out global three-dimensional
magneto-hydrodynamic simulations of the gas disk in the Galactic center. The
gravitational potential is approximated by the axisymmetric potential proposed
by Miyamoto & Nagai (1975). At the initial state, we assume a warm (~ 10^4 K)
gas torus threaded by azimuthal magnetic fields. Self-gravity and radiative
cooling of the gas are ignored. We found that buoyantly rising magnetic loops
are formed above the differentially rotating, magnetically turbulent disk. By
analyzing the results of global MHD simulations, we have identified individual
loops, about 180 in the upper half of the disk, and studied their statistical
properties such as their length, width, height, and velocity distributions
along the loops. Typical length and height of a loop are 1kpc and 200pc,
respectively. The line of sight velocity changes linearly along a loop and
shows large dispersions around the foot-points. Numerical results indicate that
loops emerge preferentially from the region where magnetic pressure is large.
We argue that these properties are consistent with those of the molecular loops
discovered by NANTEN.
