One-dimensional solitary kinetic Alfvén waves in low-beta plasma

Abstract

A two-dimensional homogeneous magnetohydrodynamic (MHD) model is applied to investigate one-dimensional solitary kinetic Alfvén waves (SKAWs) and their degenerated ion-acoustic solitons in a low-beta plasma, in which electron pressure and electron inertial effects are all taken into account. In contrast to the results of the one-dimensional SKAWs model obtained by Hasegawa and Mima [Phys. Rev. Lett. 37, 690 (1976)], Shukla et al. [J. Plasma Phys. 28, 125 (1982)], and Wu et al. [Phys. Plasmas 3, 2879 (1996)], both density hump and dip Alfvénic solitons are found to exist in the kinetic limit (2me/mi≪β≪1) and in the inertial limit (β≪2me/mi) (β=8πnTe/B02 denotes the ratio of the plasma thermal pressure to the magnetic pressure), while in the transition region (β−2me/mi), both super-Alfvénic and sub-Alfvénic solitons with a density hump or a dip are found to exist. Due to the finite-β effect, the Alfvénic solitons may degenerate into super-acoustic density hump solitons over all the range of plasma β. This result provides a one-dimensional SKAWs model to account for the observations from the Freja satellite, in which not only SKAWs accompanied by dip density solitons, but also SKAWs accompanied by hump density solitons, are found in the Earth’s ionospheric altitude.