FLUID MODELS FOR KINETIC EFFECTS ON COHERENT NONLINEAR ALFVEN WAVES .1. FUNDAMENTAL THEORY

Collisionless regime kinetic models for coherent nonlinear Alfven wave dynamics are studied using fluid moment equations with an approximate closure anzatz. Resonant particle effects are modeled by incorporatin g an additional term representing dissipation akin to parallel heat co nduction. Unlike collisional dissipation, parallel heat conduction is presented by an integral operator. The modified derivative nonlinear S chrodinger equation thus has a spatially nonlocal nonlinear term descr ibing the long-time evolution of the envelope of parallel-propagating Alfven waves, as well. Coefficients in the nonlinear terms are free of the (1-beta)(-1) singularity usually encountered in previous analyses , and have a very simple form that clarifies the physical processes go verning the large-amplitude Alfvenic nonlinear dynamics. The nonlinear ity appears via coupling of an Alfvenic mode to a kinetic ion-acoustic mode. Damping of the nonlinear Alfven wave appears via strong Landau damping of the ion-acoustic wave when the electron-to-ion temperature ratio is close to unity. For a (slightly) obliquely propagating wave, there are finite Larmor radius corrections in the dynamical equation. This effect depends on the angle of wave propagation relative to B-0 a nd vanishes for the limit of strictly parallel propagation. Explicit m agnetic perturbation envelope equations amenable to further analysis a nd numerical solution are obtained. Implications of these models for c ollisionless shock dynamics are discussed. (C) 1996 American Institute of Physics.