Stability of an Isothermal Disk with Three-Dimensional Magnetic Fields and Radial Viscous Force**The project supported by National Natural Science Foundation of China and the National Climbing-Up Programme on the Fundamental Research of China

Abstract

The stability of an isothermal thin disk with three-dimensional magnetic fields and radial viscous force is examined in this paper. We find that the radial viscous force has no influence on the stability of viscous modes. But there is more influence on the stability of magneto-acoustic modes, which is related to the perturbation wavelength and different parts of disk. Finally, we use our model to explain the long-term variability of Quasar 3C345.