The mean electromotive force generated by random Alfvén waves in a coffisionless plasma

The mean electromotive force and ponderomotive force generated by nonlinear random Alfvén waves propagating along the mean magnetic field and linear random Alfvén waves propagating in arbitrary directions in a collisionless plasma are calculated by use of Fourier analysis methods. It is shown that the a-effect can exist in the interaction between two different waves and that the magnetic turbulent diffusivity can be negative depending on the energy spectrum functions of the initial values of the magnetic and velocity perturbations. The results are applied to the substorms in the Earth's magnetosphere.