THEORY OF NEARLY PERPENDICULAR ELECTROSTATIC PLASMA-WAVES AND COMPARISON TO FREJA SATELLITE-OBSERVATIONS

The linear and nonlinear two-fluid nature of oblique electrostatic pla sma waves is explored and clarified. It is found that two distinct wav e regimes exist corresponding to propagation angles greater than or le ss than epsilon = root m(e)/m(i) with respect to the perpendicular dir ection of the magnetic field. Propagation angles greater than epsilon correspond to either the electrostatic ion cyclotron wave or the short er wavelength oblique ion acoustic wave, which are termed the fast ion cyclotron and fast ion acoustic waves respectively. Angles less than epsilon correspond to the inertial Alfven wave which is called the slo w ion cyclotron wave and in the short wavelength limit is called the s low ion acoustic wave. The slow ion-acoustic wave is found to have a p redominately ion-Boltzmann response. Initial value simulations having fast or slow ion cyclotron wave initial conditions of modest amplitude s result in nonlinear steepening and subsequent breakup into fast or s low ion acoustic waves respectively This mechanism of ion acoustic wav e generation may partially explain the origin of ion acoustic activity detected by the Freja satellite within regions of ion and electron ac celeration.