Here, the vector potential , the magnetic field and turbulent velocity are perpendicular to the z -axis with the unit vector .
All values depend only on the coordinates x , y and the time t .
The mean electromotive force is directed along the z -axis and is equal to . In the diffusion approximation one has . Zeldovich did not neglect this molecular diffusivity. Thus, his estimate is inconsistent ab initio. To see this more clearly, we write the Eqs.