VLF emissions associated with enhanced magnetospheric electrons
During periods of geomagnetic disturbances, VLF emissions and enhancements of low-energy electrons are simultaneously observed by the equatorial orbiting S/sup 3/-A (Explorer 45) satellite. These events are characterized by the following features. (1) The VLF emissions occur outside the plasmasphere in the nightside of the magnetosphere. (2) The VLF emissions consist of two frequency regimes, ne below the local electron gyrofrequency f/sub g/ and the other above (3) The VLF emissions below f/sub g/ are relatively boradband whistler mode waves characteritic of chorus and frequently have a conspicuous band of 'missing emissions' near f/sub g//2.4) The emissions above f/sub g/ are electrostatic and typically have cmponents near 3f/sub g//2. Occasionally, higher-frequency components are also observed. (5) The onset of the emissions coincides with abrupt increases outside the plasmasphere (L'mE4) in 1- to 10-keV electrons to intensities of the order of 10/sup 8/ el cm/sup -2/ s/sup -1/ sr/sup -2/ Less pronounced enhancements sometimes occur for electrons with energies as high as 70 keV. (6) The cessation of the emissions coincides with a drop in the electron intensities to their preenhancement levels, which are of the order of 10/sup 6/ el cm/sup -2/ s/sup -1/ sr/sup -1/ keV/sup -/u1 or less. This drop in low-energy electron intensities occurs before or when the satellite crosses the plasmapause back into the plasmasphere. These observed features indicate that the VLF emissions are produced by low-energy (1- to 10-keV) electrons which penetrate into the dusk-midnight sector of the magnetosphere from the geomagnetic tail during magnetic storms and substorms and drift eastward outside the plasmasphere. In this paper, events observed during geomagnetically disturbed periods in December 1971 and January 1972 are discussed. (AIP)
- Research Organization:
- Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242
- OSTI ID:
- 7236566
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 82:1
- Country of Publication:
- United States
- Language:
- English
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