Magnetic Instability in Accretion Discs with Anomalous Viscosity

Using the new model of anomalous viscosity, we investigate the magnetic instability in the accretion discs and give the dispersion formula. On the basis of the dispersion relation obtained, it is numerically shown that the instability condition of the viscous accretion disc is well consistent with that of the ideal accretion disc, namely there would be magneto-rotational instability in the presence of a vertical weak magnetic field. For a given distance R from the centre of the disc, the growth rate in the anomalous case deviates from the ideal case more greatly when the vertical magnetic field is smaller. The large viscosity limits the instability. In the two cases, the distributions of growth rate with wavenumber k approach each other when the magnetic field increases. It greatly represses the effect of viscosity.