Evolution of Nonlinear Alfven Waves in Streaming Inhomogeneous Plasmas

Abstract

A nonlinear evolution equation for waves, propagating in streaming plasmas with nonuniform Alfve n densities and inhomogeneous magnetic Ðelds, is obtained by using the reductive perturbation technique. The governing equation is a modiÐed derivative nonlinear (MDNLS) equation. The numeri-SchroŽ dinger cal solution of this equation shows that inhomogeneities exhibit their presence as an e †ective dissipation. The spatiotemporal evolution of long-wavelength Ñuctuations shows that the wave steepens as it Alfve nic propagates. High-frequency radiation is also observed in our simulations. Unlike coherent waves Alfve n in homogeneous plasmas, which can become noncoherent/chaotic only in the presence of a driver, MDNLS evolves into noncoherent/turbulent state without any driver simply because of inhomogeneities. This clearly indicates that the integrability property of the derivative nonlinear equation, SchroŽ dinger which allows coherent solitary solutions, is destroyed by inhomogeneities. Subject headings : MHD È plasmas È solar-terrestrial relations È solar wind È waves