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 multit...

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Bibliographic Details
Published in:Annales Geophysicae
Main Authors: J. A. E. Stephenson, A. D. M. Walker
Format: Article in Journal/Newspaper
Language:English
Published: Copernicus Publications 2010
Subjects:
Q
Online Access:https://doi.org/10.5194/angeo-28-47-2010
https://doaj.org/article/6cdd24c3abdd45c994491c5161372bac
Description
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.