ONE-DIMENSIONAL SOLITARY KINETIC ALFVEN WAVES IN LOW-BETA PLASMA

A two-dimensional homogeneous magnetohydrodynamic (MHD) model is appli ed to investigate one-dimensional solitary kinetic Alfven waves (SKAWs ) and their degenerated ion-acoustic solitons in a low-beta plasma, in which electron pressure and electron inertial effects are all taken i nto account. In contrast to the results of the one-dimensional SKAWs m odel 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. Pl asmas 3, 2879 (1996)], both density hump and dip Alvenic solitons are found to exist in the kinetic limit (2m(e)/m(i)much less than beta muc h less than 1) and in the inertial limit (beta much less than 2m(e)/m( i)) (beta=8 pi nTe/B02 denotes the ratio of the plasma thermal pressur e to the magnetic pressure, while in the transition region (beta-2m(e) /m(i)), both super-Alfvenic and sub-Alfvenic solitons with a density h ump or a dip are found to exist. Due to the finite-beta effect, the Al fvenic solitons may degenerate into super-acoustic density hump solito ns over all the range of plasma beta. This result provides a one-dimen sional SKAWs model to account for the observations from the Freja sate llite, in which not only SKAWs accompanied by dip density solitons, bu t also SKAWs accompanied by hump density solitons, are found in the Ea rth's ionospheric altitude. (C) 1998 American Institute of Physics. [S 1070-664X(98)03712-4].