Longitudinal variations of plasmapause radius and the propagation of VLF noise within small (ΔL ∼ 0.5) extensions of the plasmasphere

A J Smith,D L Carpenter,M Lester

doi:10.1029/gl008i009p00980

A J Smith, D L Carpenter + Show 1 more

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Journal: Geophysical Research Letters	Publication Date: Sep 1, 1981
Citations: 21	License type: cc-by

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Simultaneous broadband whistler recordings made during the International Magnetospheric Study (IMS) at the two Antarctic stations Halley and Siple have been used to study longitudinal variations in the radius of the plasmapause observed during local afternoon. In both of the two periods studied thus far, whistler‐derived equatorial electron density profiles imply an increase in plasmapause radius between the longitudes of Siple and Halley (Δϕ ∼ 30°) of ΔL ∼ 0.5. Intense VLF noise (∼2.5 kHz) was observed at Halley but not at Siple, and by echo analysis its propagation path was identified with that of a whistler component travelling close to the plasmapause within the region of larger radius. This leads to the conclusion that the noise was generated by a gyroresonance instability when energetic electrons (typically 10 keV), drifting eastwards in the plasmatrough, encountered enhanced plasma density in the small extension of the plasmasphere.

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Simultaneous broadband whistler recordings made during the International Magnetospheric Study (IMS) at the two Antarctic stations
There is evidence from previous research of variations in plasmapause radius with longitude of order 0.5 L within A ~ 30ø [ e.g. Angerami andCarpente1r,966;Carpente1r,978. These were found to occur at various local times, and are not apparently associated with the evening bulge of the plasmasphere, at which AL is typically 1-2 [ Carpenter, 1966]. Such structure is poorly documented and it was an object of spaced longitude broadband VLF measurements during the IMS to search for evidence of plasmapause structure
The purpose of the present paper is to report comparisons of data from two IMS VLF stations, Halley and Siple Stations, Antarctica

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Simultaneous broadband whistler recordings made during the International Magnetospheric Study (IMS) at the two Antarctic stations. Another source of evidence is the fact that intense VLF noise, associated with the extension of the plasmapause observed at Halley, was received only at Halley and not at Siple in the two cases.

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