Publication Date:
2014-08-30
Description:
We report observations of very-low-frequency (VLF) and extremely-low-frequency (ELF) chorus waves taken during the VLF/ELF Campaign observation with High-resolution Aurora Imaging Network (VLF-CHAIN) of 17-25 February, 2012, at subauroral latitudes at Athabasca ( L =4.3), Canada. VLF/ELF waves were measured continuously with a sampling rate of 100 kHz to monitor daily variations in VLF/ELF emissions and derive their detailed structures. We found quasi-periodic (QP) emissions whose repetition period changes rapidly within a period of 1 h without corresponding magnetic pulsations. QP emissions showed positive correlation between amplitude and frequency sweep rate, similarly to rising-tone elements. We found an event of nearly simultaneous enhancements of QP emissions and Pc1/EMIC wave intensities, suggesting that the temperature anisotropy of electrons and ions developed simultaneously at the equatorial plane of the magnetosphere. We also found QP emissions whose intensity suddenly increased in association with storm sudden commencement without changing their frequency. Falling-tone VLF/ELF emissions were observed with their rate of frequency change varying from 0.7 to 0.05 kHz/s over 10 min. Bursty-patch emissions in the lower and upper frequency bands are often observed during magnetically disturbed periods. Clear systematic correlation between these various VLF/ELF emissions and cosmic noise absorption was not obtained throughout the campaign period. These observations indicate several previously unknown features of VLF/ELF emissions in subauroral latitudes and demonstrate the importance of continuous measurements for monitoring temporal variations in these emissions.
Print ISSN:
0148-0227
Topics:
Geosciences
,
Physics
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