  We show that dwarf nova disks in quiescence have rather low magnetic Reynolds
number, of order 10^3. Numerical simulations of magnetized accretion disks
suggest that under these conditions magnetohydrodynamic turbulence and the
associated angular momentum transport is sharply reduced. This could be the
physical origin of episodic accretion in dwarf nova disks. If so, the standard
disk instability model needs to be revised.
