As DE 1 flew through the polar cusp, enhanced narrowband electrostatic waves were sometimes observed just above the electron cyclotron frequency, fce. In this report, we present wave and particle measurements from three repsentative cusp transits in order to characterize these signals and understand the conditions that favor their generation. In thse representative cases, narrowband emission intensifications occurred at frequencies between 1.1 to 1.3 fce. The emission intensities ranged between 5¿10-14 to 10-12 V2/(m2 Hz), such waves being 50 to 1000 times greater than the narrowband cyclotron-related signal levels detected in adjacent regions. Simultaneously occurring with the wave enhancements were energetic cusp electrons with energies extending up to about 500 eV. It was found that the form of the local cusp electron velocity distribution had a direct influence on the wave spectral character.

A preliminary study indicates that electron beams in the cusp can generate the enhanced signals, although generation by an anisotropic warm component cannot be ruled out. Based on an examination of many cusp transits, the occurrence of these enhanced signals appeared to have some dependency on Kp index, indicating that increased particle flows (associated with increased geomagnetic activity) seem to affect their generation. Although the exact wave/particle coupling mechanism responsible for these ehancements is difficult to identify, it is evident that the generation is directly related to the energetic cusp electrons. ¿ American Geophysical Union 1990