Ground observations of chorus following geomagnetic storms
[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...
Published in: | Journal of Geophysical Research: Space Physics |
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Main Authors: | , , |
Format: | Article in Journal/Newspaper |
Language: | unknown |
Published: |
American Geophysical Union
2004
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Subjects: | |
Online Access: | http://nora.nerc.ac.uk/id/eprint/12426/ http://www.agu.org/journals/ja/ja0402/2003JA010204/index.html |
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. |
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