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We carried out global three-dimensional magneto-hydrodynamic simulations ofdynamo activities in galactic gaseous disks without assuming equatorialsymmetry. Numerical results indicate the growth of azimuthal magnetic fieldsnon-symmetric to the equatorial plane. As magneto-rotational instability (MRI)grows, the mean strength of magnetic fields is amplified until the magneticpressure becomes as large as 10% of the gas pressure. When the local plasma$\beta$ ($ = p_{\rm gas}/p_{\rm mag}$) becomes less than 5 near the disksurface, magnetic flux escapes from the disk by Parker instability within onerotation period of the disk. The buoyant escape of coherent magnetic fieldsdrives dynamo activities by generating disk magnetic fields with oppositepolarity to satisfy the magnetic flux conservation. The flotation of theazimuthal magnetic flux from the disk and the subsequent amplification of diskmagnetic field by MRI drive quasi-periodic reversal of azimuthal magneticfields in timescale of 10 rotation period. Since the rotation speed decreaseswith radius, the interval between the reversal of azimuthal magnetic fieldsincreases with radius. The rotation measure computed from the numerical resultsshows symmetry corresponding to a dipole field.

Dynamo activities driven by magneto-rotational instability and Parker instability in galactic gaseous disk