in galaxies, proto stellar disks and in the universe just after recombination are all likely to be only partially ionised. In such a medium, the Lorentz force on the charged component will cause a slippage between it and the neutrals. Its magnitude is determined by the balance between the Lorentz force and the ion-neutral collisions. This drift, called ambipolar drift (Mestel and Spitzer 1956, Draine 1986, Zweibel 1988), can be incorporated as a field dependent addition to the fluid velocity in the induction equation. This makes the induction equation nonlinear and provides us with a model nonlinear problem to study. Such a modification of the velocity field has also been used by Pouquet [*et al.*]{} (1976) and Zeldovich [*et al.*]{} (1983) (pg. 183) to discuss nonlinear modifications to the alpha effect.

We incorporate the effects of this nonlinearity while deriving the evolution equations for both the mean field and fluctuating field correlations, in section 3 and 4. The presence of a nonlinear term due to ambipolar type drift in the induction equation implies that lower moments couple to higher order moments. Some form of closure has to be assumed. We adopt here a Gaussian closure. The mean field and the 