  Dwarf novae (DNe) are accreting white dwarfs that show eruptions due to a
thermal-viscous instability in the accretion disk. The outburst timescales
constrain $\alpha$, the ratio of the viscous stress to the thermal pressure,
and so the mechanism of angular momentum transport. The eruptive state has
$\alpha\approx0.1$ while the quiescent state has $\alpha\approx0.03$. Turbulent
transport due to the magneto-rotational instability (MRI) is generally
considered to be the source of angular momentum transport in DNe. Here, we
perform 3D local magnetohydrodynamic (MHD) shearing box simulations including
vertical stratification, radiative transfer and a net constant vertical
magnetic flux to investigate how transport changes between the outburst and
quiescent states of DNe. We find that a constant $B_z$ provides a higher
$\alpha$ in quiescence than in outburst, in opposition to what is expected.
Including resistivity quenches MRI turbulence in quiescence, suppressing
transport, unless the magnetic field is high enough, which again leads to
$\alpha\approx0.1$. A major difference between simulations with a net poloidal
flux and simulations without is that angular momentum transport in the former
is shared between turbulent and wind-driven transport. We find that wind-driven
transport dominates in quiescence even for low magnetic fields $\sim 1$ G. This
can have a major impact on observational signatures since wind-driven transport
does not heat the disk. Furthermore, wind transport cannot be reduced to an
$\alpha$ prescription. We provide fits for $\alpha$ and the wind torque with
$\beta$, ratio of thermal to magnetic pressure. We conclude that the evolution
of the thermal-viscous instability, and its consequences on the outburst cycles
of CVs, needs to be seriously revised to take into account that most of the
accretion energy may be carried away by a wind instead of being locally
dissipated.
