WAVE ENVIRONMENT INSIDE AN INVERTED-V ELECTRON EVENT OBSERVED BY FREJA

We present an analysis of the wave environment observed inside an inve rted-V electron event at an altitude of 1700 km, occurring in the upwa rd directed current with intensity of a few muAm-2. During the analyze d event we observe that precipitating auroral electrons (approximately 2 keV) generate intense (40 mV/m) auroral hiss with peak power concen trated at the lower hybrid frequency f(lh) almost-equal-to f(pi), and weak Langmuir waves at f(pe). The low frequency turbulence observed wi thin the event is found to be composed of a mixture of Alfven waves, O + cyclotron waves, multi-ion resonances, and ion sound waves. The LH w aves appear to interact modulationally with O+ and ion sound waves. Fr om the observed values Of f(lh) and multi-ion resonance frequencies it is possible to estimate three-ion composition of plasma with represen tative values of [23, 19, 58] percent for normalized number densities of [H+, He+, O+], respectively.