NARROW-BAND PLASMAPAUSE HISS

Narrow-band plasmapause hiss around 5 kHz was often observed in the vicinity of the plasmapause invariant latitude by ISIS-1 and ISIS-2. Frequency-time spectra of the hiss are similar to those of ground narrow-band 5 kHz hiss observed at mid- and low-latitudes. Statistically, the occurrence rate of the narrow-band plasmapause hiss is maximum at invariant latitudes 58 degrees-59 degrees for Kp= 0 - 3 and extends over a broader range of 56 degrees to 60 degrees for Kp= 4 - 6. The geomagnetic local time (MLT) distribution of the hiss occurrence rate peaks at 18 - 21 hours MLT for Kp= 0 - 3 and at 0 - 3 hours MLT for Kp= 4 - 6. The peak of the hiss occurrence rate in the local time variation may be due to the flow direction of drifting electrons from the magnetotail. The narrow-band plasmapause hiss seems to be generated by cyclotron instabilities of electrons with an energy of a few keV in the vicinity of the plasmapause.