  The interstellar magnetic field strength and gas 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 low ionization
fraction, in which case ion-neutral drift, or ambipolar diffusion, leads to
appreciable slip of the field and tends to make it more uniform. We show that
turbulence enhances the rate of ambipolar drift, and that this may explain the
surprisingly low fieldstrengths sometimes seen in dense interstellar gas.
