Simultaneous observations of waves and ion beams by the Viking satellite can be used to study wave-particle interaction on auroral field lines. The characteristics of the observed beams may be rather stable during long periods, at least up to 20 minutes. However, the wave characteristics during such events may vary within seconds. Sometimes the wave experiment detects narrowband EHC waves, sometimes broadband emissions up to several times the proton gyro frequency, and sometimes just an increased level of turbulence. The variations of the wave characteristics may at least partly be due to variations in a cool, low density electron population. ¿American Geophysical Union 1987