PARKERS INSTABILITY AND VISCOSITY IN QUIESCENT CATACLYSMIC VARIABLE DISCS

Reduced ionization in quiescent cataclysmic variable discs has been su ggested as a possible explanation for dwarf nova outbursts. It has bee n shown that a Self-consistent magnetic dynamo can operate in a fully ionized accretion disc and so provide an effective (magnetic) viscosit y. The growth rate of Parker's instability (magnetic buoyancy) in part ially ionized media is calculated along with the dispersion relation. Combined with the Balbus-Hawley instability in a similar medium, magne tic reconnection and the dynamo model are generalized for partially io nized discs. It is found that the Shakura-Sunyaev viscosity parameter does not decrease for moderately low ionization fractions typical of t he discs of cataclysmic variables in the quiescent phase.