Coherence between radar observations of magnetospheric field line resonances and discrete oscillations in the solar wind
Field line resonances have been observed for decades by ground-based and in situ instruments. The driving mechanism(s) are still unclear, although previous work has provided strong grounds that coherent waves in the solar wind may be a source. Here we present further evidence, with the use of mu...
| Main Authors: | , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2010-01-01
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| Series: | Annales Geophysicae |
| Online Access: | https://www.ann-geophys.net/28/47/2010/angeo-28-47-2010.pdf |
| Summary: | Field line resonances have been observed for decades by ground-based and in
situ instruments. The driving mechanism(s) are still unclear, although
previous work has provided strong grounds that coherent waves in the solar
wind may be a source. Here we present further evidence, with the use of
multitaper analysis, a sophisticated spectrum estimation technique. A set of
windows (dpss tapers) is chosen with characteristics that best suit the width
of the narrowband peaks to be identified. The orthogonality of the windows
allows for a confidence level (of say 95%) against a null hypothesis of a
noisy spectrum, so that significant peaks can be identified. Employing
multitaper analysis we can determine the phase and amplitude coherence at the
sampling rate of the data sets and, over their entire duration. These
characteristics make this technique superior to single windowing or wavelet
analysis. A high degree of phase and amplitude (greater then 95%) coherence
is demonstrated between a 2.1 mHz field line resonance observed by the SHARE
radar at Sanae, Antarctica and the solar wind oscillation detected by WIND
and ACE satellites. |
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| ISSN: | 0992-7689 1432-0576 |