Observations on the spatial structure of pulsating electron precipitation accompanying low frequency hydromagnetic disturbances in the auroral zone

Abstract

Low-frequency hydromagnetic disturbances which are generated in the sunlit part of the distant magnetosphere and propagate as transverse waves to auroral latitudes are accompanied by pulsating electron precipitation and ionospheric absorption of cosmic radio noise with a similar temporal behavior. The region over which this pulsating activity occurs is belt-like, ≳1000 km long and ∼100–400 km across. Sometimes the instantaneous pattern of precipitation exhibits spatial structure over these dimensions, but at least on one occasion the pulsations were in phase over a large region near the noon meridian. A unique acceleration process does not appear to be required, as the bremsstrahlung X-ray spectrums obtained for the pulsations are not essentially different from those observed during activity preceding or following these events. The statically trapped radiation is eliminated as a possible source, and some mechanisms involving local energization are briefly discussed.