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Ground observations of chorus following geomagnetic storms

Smith, A.J.; Horne, R.B.; Meredith, N.P.. 2004 Ground observations of chorus following geomagnetic storms. Journal of Geophysical Research, 109 (A2), A02205. 10.1029/2003JA010204

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Abstract/Summary

[1] It has been suggested that whistler mode chorus waves play a role in acceleration and loss of radiation belt electrons during geomagnetic storms. In this paper we present data from a complete solar cycle ( 1992 - 2002) of nearly continuous (> 95%) VLF/ELF observations from the VLF/ELF Logger Experiment (VELOX) instrument at Halley station, Antarctica (76 degreesS, 27 degreesW, L = 4.3), to determine whether there is statistical evidence for enhanced whistler mode chorus waves during geomagnetic storms. The data comprise 1 s resolution measurements of ELF/VLF wave power in eight frequency bands from 500 Hz to 10 kHz. The variations in chorus activity during several storms, including the well-studied Bastille Day event ( 14 July 2000), show enhanced wave power but are variable from event to event. The average behavior has been found from a superposed epoch analysis using 372 storms with minimum Dst less than - 50 nT, including 82 large storms with minimum Dst less than - 100 nT. Compared with average prestorm levels, the chorus intensity decreases in the storm main phase but is enhanced in the recovery phase, typically maximizing a day after the storm onset. At 1 kHz the enhancement is independent of storm severity, suggesting a saturation effect, whereas larger storms produce larger wave intensities at higher frequencies in the chorus band ( e. g., 3 kHz), which is interpreted as the effect of a chorus source region located on lower L shells than for weaker storms. The storm chorus enhancement maximizes at postdawn local times, leading to a 24 hour recurrence effect. A long-enduring depression in wave intensities, of 10 days or more, is found near the top of the normal chorus band ( similar to 5 kHz). We suggest that this is due to precipitation from enhanced relativistic particle fluxes affecting the subionospheric propagation of spherics from nearby thunderstorm regions across the L = 2 - 4 zone.

Item Type: Publication - Article
Digital Object Identifier (DOI): 10.1029/2003JA010204
Programmes: BAS Programmes > Antarctic Science in the Global Context (2000-2005) > Magnetic Reconnection, Substorms and their Consequences
ISSN: 0148-0227
Additional Keywords: chorus, geomagnetic storms, electron acceleration, relativistic electrons, whistler mode waves, wave-particle interactions
NORA Subject Terms: Atmospheric Sciences
Date made live: 23 Feb 2012 14:48
URI: http://nora.nerc.ac.uk/id/eprint/12426

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