Observation of Ionospheric Alfven Resonances at 1--30 Hz and their superposition with the Schumann Resonances

Beggan, C.D.; Musur, M.. 2018 Observation of Ionospheric Alfven Resonances at 1--30 Hz and their superposition with the Schumann Resonances. Journal of Geophysical Research Space Physics, 123 (5). 4202-4214.

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Long-term measurements of the high-frequency magnetic field (0.1--100 Hz) have been made at Eskdalemuir Observatory in the UK since September 2012. We analyze five years of dynamic spectrograms to examine the occurrence and behavior of the Schumann and Ionospheric Alfven Resonances (IAR), and Pc1 pulsations. The resonances, observed as diffuse bands, arise from reflections of energy both within the earth-ionosphere cavity and from the non-linear conductivity gradient of the ionosphere. Schumann Resonances (SR) occur continuously but IAR are observed to arise at local night time in ~50% of days in the dataset. Typically, IAR are found at frequencies of 1--8 Hz, but we find them extending out to 30 Hz and strongly superimposing over the first three Schumann Resonances around 9% of the time. These phenomena include constructive and destructive interference, non-linear frequency changes over the span of several hours and polarity enhancements. In addition, the magnitude of the IAR do not decline rapidly with frequency as often proposed. We find the IAR and their superposition with SR are strongly controlled by season and geomagnetic activity. We compare six days with the most unusual IAR behavior in the dataset to ionosonde measurements of f0F2, a proxy for ionospheric conductivity, but find little correlation. We suggest that, as current theoretical modelling does not account for these observations, further work is needed to understand how they arise.

Item Type: Publication - Article
Digital Object Identifier (DOI):
ISSN: 0148-0227
Date made live: 23 May 2018 08:41 +0 (UTC)

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