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Where spatial gradients in the amplitude of an Alfven wave are non-zero, anonlinear magnetic-pressure gradient acts upon the medium (the ponderomotiveforce). We investigate the nature of such a force in inhomogeneous 2.5D MHDplasmas by analysing source terms in the nonlinear wave equations for thegeneral case of inhomogeneous B and {\rho}, and consider supporting nonlinearnumerical simulations. Our equations indicate there are two distinct classes ofponderomotive effect induced by Alfven waves in general 2.5D MHD, each withboth a longitudinal and transverse manifestation; i) Geometric Effects:Gradients in the pulse geometry relative to the background magnetic field causethe wave to sustain cospatial disturbances, the longitudinal and transversedaughter disturbances - where we report on the transverse disturbance for thefirst time. ii) Grad (c_A) Effects: Where a pulse propagates through aninhomogeneous region (where the non-zero gradients in the Alfven-speed profileare non-zero), the nonlinear magnetic-pressure gradient acts to accelerate theplasma. Transverse gradients (phase mixing regions) excite independentlypropagating fast magnetoacoustic waves (generalising the result of Nakariakovet al. 1997, Solar Physics, 175, 93) and longitudinal gradients perturb alongthe field (thus creating static disturbances in {\beta} = 0, and slow waves in{\beta} \= 0).  We additionally demonstrate that mode conversion due the nonlinear Lorentzforce is a one-way process, and does not act as a mechanism to nonlinearlygenerate Alfven waves due to propagating magnetoacoustic waves. We concludethat these ponderomotive effects are induced by an Alfven wave propagating inany MHD medium, and have the potential to have significant consequences on thedynamics of energy transport and aspects of dissipation provided the system issufficiently nonlinear and inhomogeneous.

On ponderomotive effects induced by Alfven waves in inhomogeneous 2.5D MHD plasmas