ULF WAVE MEASUREMENTS ONBOARD THE INTERBALL AURORAL PROBE

The IESP experiment implemented onboard the Interball auroral probe me asures the six components (3B, 3E) of the waves in the ULF range: 0.1- 10 Hz and from time to time 0-30 Hz. Two different kinds of waves have been observed in the auroral region at altitudes between 10 000 and 2 0 000 km: (1) electrostatic emissions which consist of quasi-monochrom atic structures with frequencies above the oxygen gyrofrequency, super imposed on a wide band signal interpreted as a Doppler broadening, (2) electromagnetic wide band spectrum fluctuations. These emissions are interpreted as current-driven electromagnetic or electrostatic ion cyc lotron waves. The electromagnetic/electrostatic character is controlle d by the plasma parameter beta(i) and by the O+ concentration.