Morphology of VLF hiss zones and their correlation with particle precipitation events

Observations of wide-band hiss in the frequency range 4–9 kc/s made at 13 stations in both hemispheres since last sunspot maximum show that hiss is generated in certain zones. Apparently these zones are the same as the zones of auroral precipitation and so are approximately circular, with their centers close to the magnetic midnight meridian some few degrees from the geomagnetic poles. Hiss is not observed equally often everywhere in these zones; there is a maximum of the occurrence at about 70° magnetic latitude shortly before magnetic midnight. Hiss seems to be a rare phenomenon at the very highest latitudes close to the geomagnetic poles. Observations by the Alouette 1 satellite of very intense electron fluxes at latitudes higher than the boundary of the outer radiation belt show that these fluxes are very well correlated to ground-based hiss observations both in space and in time. It is therefore suggested that these very intense electron fluxes are responsible for, or at least closely connected with, the generation of hiss. Owing to the positive correlation between hiss, activity and high-latitude electron fluxes, which again are correlated with the intensity variations in the outer radiation belt, it would appear to be possible to monitor, from the ground, high-intensity electron fluxes in the polar regions and intensity variations in the outer radiation belt.