Plasma waves associated with energetic particles streaming into the solar wind from the Earth's bow shock

Abstract

In the upstream solar wind, three dominant types of plasma waves are observed associated with energetic particle streams coming from the earth's bow shock: ion acoustic waves, electron plasma oscillations, and whistler mode waves. The ion acoustic waves occur simultaneously with either ion beams or a dispersed ion population in the energy range from ∼0.5 to >45 keV. These short‐wavelength electrostatic waves are very impulsive, and the peak amplitudes increase with increasing ion flux and at spatial gradients in the energetic ion densities. The electron plasma oscillations are long‐wavelength nearly monochromatic electrostatic waves which are closely correlated with the flux of low‐energy electrons, especially in the 0.2–1.5 keV range. In the presence of only enhanced electron fluxes, the average amplitudes of the electron plasma oscillations approach the peak amplitudes. Amplitudes near 10 mV/m have been observed, although amplitudes from 0.1 to 1.0 mV/m are typical. In the presence of the dispersed ion component, electron plasma oscillations decrease in amplitude and become more impulsive. Electromagnetic waves with frequencies below 200 Hz are observed when either ion beams or dispersed ion distributions are present. These waves are usually weak and very impulsive. For these waves the refractive index determined from the wave B to E ratio is consistent with whistler mode radiation. Whistler mode waves also occasionally occur in association with electron plasma oscillations.