Characteristics of narrow band mid-latitude hiss observed in the topside ionosphere

Frequency-time spectra are presented of four examples of typical midlatitude hiss found in ISIS VLF electric field data (50 Hz-30 kHz) received at Syowa Station, Antarctica under geomagnetically quiet and moderate conditions. Latitudinal and local time distributions are also presented of the occurrence rates of midlatitude hiss during geomagnetically quiet and moderate (Kp=0-3) and disturbed (Kp=4-6) periods. The data were obtained statistically from 507 satellite passes between December 1976 and January 1983. The peak occurrence rate of midlatitude hiss at invariant latitude 60 deg (plasmapause latitude) and that in the late evening sector suggest that the narrowband midlatitude hiss is caused by the cyclotron resonance instability of energetic electrons which are injected from the magnetotail and drift eastward around the plasmapause.