Solitary kinetic Alfvén waves in the two-fluid model

Abstract

Employing the two-fluid model, a generalized Sagdeev equation governing solitary kinetic Alfvén waves (SKAWs) and the criterion for the existence of SKAWs, which are valid for different ranges of plasma pressure parameter β, are presented. In the limit cases of β≫me/mi and β≪me/mi, the present results correspond, respectively, with conclusions obtained by Hasegawa et al. [Phys. Rev. Lett. 37, 690 (1976)] and by Shukla et al. [J. Plasma Phys. 28, 125 (1982)], that is, SKAWs accompanied by, respectively, hump and dip density solitons for β≫me/mi and β≪me/mi. However, for the case of β∼me/mi, the present results show that SKAWs accompanied by both hump and dip density solitons are possible, and lead to KdV solitons in the small amplitude limit. In addition, the possibility for applying these results to electromagnetic spikes observed by the Freja scientific satellite is discussed [detailed information about the Freja satellite experiments can be found in serial papers presented in Space Sci. Rev. 70, Nos. 3/4 (1994)].