Ambipolar Drift in a Turbulent Medium

The interstellar magnetic field strength and density are observed to be correlated, but there is a large dispersion in this relation. In particular, the magnetic field is often observed to be weaker than expected. It is usually assumed that the field is frozen into the gas except at very high density and low ionization fraction, in which case ion-neutral drift, or ambipolar diffusion, leads to appreciable slip of the field relative to the neutral gas and tends to make the strength of the field more uniform. The purpose of this paper is to show that ion-neutral drift is significantly faster in a turbulent medium than in a quiescent one. We suggest that this fast ambipolar diffusion can explain the surprisingly low magnetic fieldstrengths sometimes observed in dense interstellar gas. Subject headings: ISM: magnetic fields, turbulence, MHD