THEORY AND SIMULATION OF LOW-FREQUENCY PLASMA-WAVES AND COMPARISON TOFREJA SATELLITE-OBSERVATIONS

One-dimensional models of obliquely propagating nonlinear plasma waves were formulated and solved both analytically and numerically to inter pret recent Freja satellite observations of low-frequency plasma waves detected in the low-altitude auroral magnetosphere. Analytic calculat ions revealed four types of steady state waves solutions. Time depende nt initial value numerical calculations were compared to the steady st ate solutions and to Freja observations. One type of steady state wave solution emerged in the long time limit from the initial sinusoidal w aves; however, the initial value simulations agreed best with the obse rvations during the nonlinear steepening phase of the initial waveform at a time well before a steady state was reached. From this result we concluded that many of the low altitude auroral waves Freja has detec ted were oblique inertial Alfven waves that had nonlinearly steepened due to propagation into a region of lower Alfven speed. The nonlinear steepening was found to produce very large parallel currents. The curr ent is sufficiently high to excite parallel electron drift instabiliti es, which may lead to electron and ion energization and enhanced dissi pation of auroral are energy.