  The eruptive cycles of dwarf novae (DN) are thought to be due to a
thermal-viscous instability in the accretion disk surrounding the white dwarf
(WD). This model has long been known to imply a stress to pressure ratio \alpha
~0.1 in outburst compared to \alpha ~ 0.01 in quiescence. Such an enhancement
in $\alpha$ has recently been observed in simulations of turbulent transport
driven by the magneto-rotational instability (MRI) when convection is present,
without requiring a net magnetic flux. We independently recover this result by
carrying out PLUTO MHD simulations of vertically stratified, radiative,
shearing boxes with the thermodynamics and opacities appropriate to DN. The
results are robust against the choice of vertical boundary conditions. The
thermal equilibrium solutions found by the simulations trace the well-known
S-curve in the density-temperature plane. We confirm that the high values of
\alpha ~ 0.1 occur near the tip of the hot branch of the S-curve, where
convection is active. However, we also present thermally-stable simulations at
lower temperatures that have standard values of \alpha ~ 0.03 despite the
presence of vigorous convection. We find no simple relationship between \alpha
and the strength of the convection, as measured by the ratio of convective to
radiative flux. The cold branch is only very weakly ionized so, in the second
part of this work, we studied the impact of non-ideal MHD effects on transport.
We include resistivity in the simulations and find that the MRI-driven
transport is quenched (\alpha ~ 0) below the critical density at which the
magnetic Reynolds number R_m \leq 10^4. This is problematic as X-ray emission
observed in quiescent systems requires ongoing accretion onto the WD. We verify
that these X-rays cannot self-sustain MRI-driven turbulence by photo-ionizing
the disk and discuss possible solutions to the issue of accretion in
quiescence.
