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We perform global three-dimensional MHD simulations of unstratified accretiondisks in cataclysmic variables (CVs). By including mass inflow via an accretionstream, we are able to evolve the disk to a steady state. We investigate therelative importance of spiral shocks and the magnetorotational instability(MRI) in driving angular momentum transport and how each depend on the geometryand strength of seed magnetic field and the Mach number of the disk (where Machnumber is ratio of the azimuthal velocity and the sound speed of gas). We use alocally isothermal equation of state and adopt temperature profiles that areconsistent with CV disk observations. Our results indicate that the relativeimportance of spiral shocks and MRI in driving angular momentum transport iscontrolled by the gas Mach number and the seed magnetic field strength. MRI andspiral shocks provide comparable efficiency of angular momentum transport whenthe disk Mach number is around 10 and the seed magnetic field has plasma$\beta=400$ (where $\beta$ is ratio of gas pressure and magnetic pressure). TheMRI dominates whenever the seed field strength, or the disk Mach number, isincreased. Among all of our simulations, the effective viscosity parameter$\alpha_{eff} \sim 0.016-0.1$ after MRI saturates and the disk reaches steadystate. Larger values of $\alpha_{eff}$ are favored when the seed magnetic fieldhas vertical components or the flow has stronger magnetization ($1/\beta$). Ourmodels all indicate that the role of MRI in driving angular momentum transportthus mass accretion in CV disks is indispensable, especially in cool disks withweak spiral shocks.

Global MHD Simulations of Accretion Disks in Cataclysmic Variables (CVs): II The Relative Importance of MRI and Spiral Shocks