On the dynamo driven accretion disks

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We add the α- effect in the dynamo driven accretion disk model proposed by Tout & Pringle (1992), i.e., a dynamo model depends on the physical processes such as Parker instability, Balbus-Hawley instability, magnetic field reconnection and α-ω mean field dynamo as well. The α- effect in the dynamo mechanism is determined by the strength of turbulence of the accretion flow. When the turbulent Mach number Mₜ is less than 0.25, the solutions of the magnetic fields oscillate around their equilibrium values. The increase of the value of Mₜ makes the amplitude of the oscillation smaller and the period longer, but does not affect the equilibrium values. The Shakura-Sunyaev viscosity parameter αSS oscillates around the equilibrium value of 0.33. When the turbulent Mach number Mₜ is larger than 0.25, the magnetic field components reach a stable state. In the non-linear dynamo region, the critical turbulent Mach number Mₜ is 0.44 rather than 0.25. The oscillating magnetic fields and viscosity parameter can explain the basic properties of the dwarf nova eruptions and some properties of quiescent disks (Armitage et al. 1996).