The α-effect generated by standing Alfvén waves

Abstract
The mean electromotive force generated by nonlinear standing Alfvén waves propagating along the mean magnetic field is investigated. It is shown that the α-effect can exist owing to the interaction between oppositely propagating two waves, provided that the initial fields have non-zero helicity. The result is discussed in the context of field-aligned currents and periodic particle flux variations in the earth's magnetosphere.