Generation of electron-acoustic waves in the magnetosphere

Generation of electron-acoustic waves (EAWs) is examined in an unmagnetized , four-component plasma consisting of stationary cold and hot Maxwellian el ectrons, drifting electron beam and ions. The addition of hot background el ectrons to the previously existing three-component model reduces the excite d EAW frequencies and growth rates. Electrostatic linear dispersion equatio n is solved analytically for the growth rate and real frequency. The linear theory of EAWs is applied to the dayside auroral zone and other regions of the magnetosphere. The mechanism can generate frequencies over a wide rang e of 5 Hz-6 kHz, 3 Hz-4 kHz and 5 Hz-6 kHz in the dayside auroral zone, pla sma sheet boundary layer and polar cusp, respectively. The e-folding time o f the instability is of the order of a few milliseconds, and the waves are expected to grow nonlinearly to large amplitudes. Our four-component model can explain the broadband electrostatic noise (BEN) observations below the total electron plasma frequencies in these regions fairly well. (C) 2001 El sevier Science Ltd. All rights reserved.