Kinetic density fluctuations associated with envelope-modulated Alfvén waves in a solar wind plasma

A nonlinear evolution equation of envelope-modulated Alfvén waves including both ion kinetic effects and ion acoustic waves (KTDNLS: kinetically modified triple-degenerated derivative nonlinear Schrödinger equation) is discussed. The consistency with the kinetic model of the ponderomotive density fluctuation (KDNLS: kinetically modified derivative nonlinear Schrödinger equation) is set as the constraint to the resultant model. To close the system, modeling of the second-order specific heat ratio is demonstrated. The transverse stability analysis of Alfvén waves using the KTDNLS is carried out. The resultant nonlinear evolution equation is similar to the one obtained from the KDNLS, which shows that the ion kinetic effects enhance the transverse instabilities.