Convective filamentation instability of circularly polarized Alfvén waves

A convective instability that leads to the filamentation of large-amplitude Alfvén waves and generates nonoscillatory spatially growing density fluctuations is investigated by using a two-fluid plasma model. Based on linear perturbation analysis for a four-wave parametric coupling process, the dispersion relations of the instability for both a right- and left-hand circularly polarized Alfvén pump are derived. They are then solved numerically for the dependences of the threshold fields and growth rates on the wavenumber k of the nonoscillatory mode, the beta of the plasma, and the frequency of the pumps, for both right- and left-hand circularly polarized Alfvén pumps. The relevance of the proposed instability with some observations in the space plasmas is discussed.