THE FORMATION OF SHARP STRUCTURES BY AMBIPOLAR DIFFUSION

The effect of ambipolar diffusion is investigated using simple numeric al models. Examples are shown where sharp structures develop around ma gnetic nulls. In contrast to the case of ordinary diffusion, the magne tic field topology is conserved by ambipolar diffusion. This is demons trated in an example where differential rotation winds up an initially uniform magnetic field and brings oppositely oriented field lines clo se together. It is argued that ambipolar diffusion produces structures of scales small enough for reconnection to occur.