The mean electromotive force generated by random Alfvén waves in a collisionless non-uniform plasma

The mean electromotive force produced by random hydromagnetic waves in a collisionless plasma is investigated taking into account non-uniformities in the mean magnetic field, fluid velocity and plasma density. It is shown that the mean electromotive force associated with gradients in mean quantities and the helicity spectrum function of the random velocity field exists and has a component parallel to the mean magnetic field which is associated with field-aligned gradients in mean quantities and density gradients parallel to the mean flow. The results are discussed in the context of the field-aligned currents in the earth's magnetosphere.