Source regions deduced from attenuation bands in VLF saucers

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Abstract
Fourteen VLF saucer events exhibiting attenuation bands related to the proton gyrofrequency were studied to check the usual assumption that saucers are due to upgoing whistler mode waves. It was found that most of the 14 saucers exhibited attenuation bands with proton gyrofrequencies smaller than the local proton gyrofrequency at the satellite. Assuming that the generation or interaction region with its characteristic proton gyrofrequency imprints its signature on the saucers originating at or propagating through that location, these observations suggest that the majority of the 14 saucer waves propagated down to the ISIS 2 satellite. The generation/interaction regions of these saucers exhibiting attenuation bands were also found to be located in the 2300–0100 local time sector between 60° and 70° geomagnetic latitude, with a tendency to be at lower latitudes for higher geomagnetic activity. Although the attenuation bands are usually horizontal, a new observation is the positively sloping attenuation bands, suggesting larger proton gyrofrequency values with time. When combined with already published data on particle precipitation, these observations imply that downgoing suprathermal electrons are also responsible for saucers.