Generation of electron plasma waves in the upstream solar wind

Electron plasma waves with amplitudes as high as 10 mV/m have been measured in the electron foreshock region of the earth's bow shock. It is shown that a population of stable suprathermal electrons of the type observed can produce the measured level of enhanced fluctuations without becoming unstable. The steady state wave level is given by the balancing between emission and absorption. The apparent association of fluctuation enhancements with sharp changes in electron fluxes can be understood in terms of modification of the electron distribution due to acceleration processes. The expected 2ωpe radiation from the model is consistent with the observations.