Angular momentum transport and dynamo-effect in stratified, weakly magnetic disks

The magnetic shear instability is reviewed numerically in the local box app roximation for a Kepler disk. Special emphasis is laid on the relation betw een the viscosity-alpha and dynamo-alpha in case a mean magnetic held is ge nerated. Self-sustaining 'turbulence' is initiated by the instability which acts sim ultaneously as dynamo and efficient outward transporter for angular momentu m. The Shakura-Sunyaev parameter alpha ss is estimated to approximate to 1. 5 10(-2) for an adiabatic disk model, and the contribution from the Maxwell stress dominates over that of the Reynolds stress by a factor of 4. In case of stress-free, normal-B vertical boundary conditions, a non-zero m ean magnetic field mainly oriented in azimuthal direction is generated. Thi s mean field turns out time-dependent in a quasi-periodic manner. Box reson ance oscillations in the horizontal velocities for a limited time lead to a n enhanced, violently fluctuating Reynolds stress associated with a reduced magnetic activity. The resulting (dynamo-) alpha-effect is negative in the upper disk plane and positive in the lower disk plane, it is small and hig hly noisy.