Dynamo-driven accretion disks and dwarf nova eruptions

We explore the consequences of a magnetic dynamo origin for the viscosity in accretion disks, for the structure and evolution of disks in dwarf nova systems. We propose that the rapid cooling that sets in at the end of a dwarf nova eruption acts to inhibit the Balbus-Hawley instability, and thereby to quench dynamo action and so reduce disk viscosity. We demonstrate that a modified disk instability model can reproduce the basic properties of dwarf nova eruptions, as well as some properties of quiescent disks. We also discuss some observational consequences of our model.