Publication Date:
1979-01-01
Description:
Cosmic radio noise data, acquired with a fast-response 30 MHz riometer at Siple Station, Antarctica (L≈4), show evidence of weak impulsive quasi-periodic variations in ionospheric absorption. Significant amplitude variations approaching 0.02 dB, approximately the statistical noise limit of the measurement, have been measured. An event typically will consist of 3 to 5 cycles of oscillation (∽60 to 90 sec period) and can occur during locally disturbed or quiet geomagnetic conditions. Usually the oscillations are not related closely to magnetic field fluctuations as measured on the ground at Siple or in the conjugate area. Conjugate bremsstrahlung X-ray data, available for one event, suggest that these absorption variations are caused by the impact on the ionosphere of a modulated flux of energetic electrons from the magnetosphere. Limited statistics on the location of the plasmapause suggest that these events occur close to, but on either side of, the boundary of the plasmasphere. These absorption oscillations may be another manifestation of the process that produces short-term intensity and phase variations in fixed-frequency sub-ionospheric LF and VLF wave propagation. Further studies of this unique modulated precipitation/absorption phenomenon and its relationship to hydromagnetic wave disturbances in the magnetosphere will be conducted with a set of riometer and magnetometer stations appropriately sited in a latitude array. © 1979, Society of Geomagnetism and Earth, Planetary and Space Sciences. All rights reserved.
Print ISSN:
0022-1392
Topics:
Geosciences
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