Nonlinear evolution of dispersive Alfvén waves and the effect of magnetic islands in the solar wind plasmas

Abstract

Solar wind is often known as a source of energizing Earth's magnetosphere and it is a highly complex system displaying various phenomena. Alfvén waves are believed to play a crucial role in its dynamics. The dispersive Alfvén waves (DAWs) may explain various plasma processes, for example, the transfer of energy over different length scales, particle energization, etc., and it is one of the promising sources in the context of magnetic reconnection. We develop a model based upon the two-fluid approximation to study the Alfvén waves, which becomes dispersive on account of the finite frequency correction of the wave, propagating in the medium with a pre-existing chain of magnetic islands and under the impact of the background density fluctuations arising from the ponderomotive nonlinearity of the wave. In the present paper, we study how the dispersive Alfvén waves (DAWs) contribute in the two significant space phenomena, i.e., turbulence and magnetic reconnection. We show that DAWs are important in the generation of localized (coherent) structures and the formation of current sheets. A strong and weak DAW is studied using numerical simulation and semi-analytical approaches in the vicinity of magnetic reconnection sites, i.e., reconnection induced magnetic islands. For the case of strong DAWs, the power spectral density of the fluctuations has been obtained for studying the behavior of the generated turbulence in the solar wind plasmas at 1 AU. The consistency of these results with the observational findings is also reported.