MAGNETIC BUOYANCY AND THE GALACTIC DYNAMO

Concentrating on the role of the Parker instability, we consider an intrinsic instability of the magnetic field as a possible origin of the alpha-effect taking part in the dynamo action. We examine the possibility that the magnetic field is concentrated in braked, isolated flux tubes extended between molecular clouds. We estimate that the ionized gas moving along the tube of the total length 100pc, the mean intercloud distance, acquires due to Coriolis force the cyclonic velocity congruent-to 1.5kms-1. The balance of the drag force and the buoyancy force acting on the rising flux tubes establishes the characteristic velocity of rise congruent-to 1kms-1. We point out that these slow flux tube velocities, can lead to the comparatively small diffusivity coefficient eta(T) congruent-to 0.06 . 10(26)cm2s-1. The estimation of helicity in this model gives alpha congruent-to 0.6kms-1. This result leads to the conclusion that the dynamo number D = R(alpha)R(omega) can be increased even by a factor of 100 with respect to the standard model.