Density fluctuations induced by modulational instability of parallel propagating alfven waves with beta(f) similar to 1

摘要

Density fluctuations generated by envelope modulation of Alfven waves are studied when the sound to Alfven velocity ratio C-S/C-A ( root Bf) similar to 1, using a kinetic version of the triple-degenerate derivative nonlinear Schrodinger (TDNLS) equation set, in which both right- and left-hand polarized quasi-parallel Alfven waves as well as sound waves, all propagating in the same direction, are included. In the model, kinetic effects along the longitudinal direction are introduced phenomenologically. Long time evolution of the Alfven waves are discussed by numerically time integrating the obtained TDNLS model. The TDNLS model reproduces not only features of the well-known derivative nonlinear Schrodinger (DNLS) model, but also results obtained from more general frameworks. Numerical results suggest that the nonlinearly-driven modulational instability can play important roles in the dissipation of both right-and left-hand polarized Alfven waves in the solar wind.