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| Titel |
Observations and modelling of the wave mode evolution of an impulse-driven 3 mHz ULF wave |
| VerfasserIn |
J. D. Borderick, T. K. Yeoman, C. L. Waters, D. M. Wright |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 28, no. 9 ; Nr. 28, no. 9 (2010-09-22), S.1723-1735 |
| Datensatznummer |
250016884
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| Publikation (Nr.) |
 copernicus.org/angeo-28-1723-2010.pdf |
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| Zusammenfassung |
| A combination of an HF Doppler sounder, a network of ground magnetometers,
upstream solar wind monitors and a numerical model is used to examine the
temporal evolution of an Ultra Low Frequency (ULF) wave. The event occurred
on 16 April 1998 and followed a solar wind density and pressure increase seen
in the upstream ACE spacecraft data. The magnetometer and HF Doppler sounder
data show that the event develops into a low-m (−6) field line
resonance. HF signals that propagate via the ionosphere exhibit Doppler
shifts due to a number of processes that give rise to a time-dependent phase
path. The ULF electric and magnetic fields are calculated by a
one-dimensional model which calculates the wave propagation from the
magnetosphere, through the ionosphere to the ground with an oblique magnetic
field. These values are then used to determine a model HF Doppler shift which
is subsequently compared to HF Doppler observations. The ULF magnetic field
at the ground and Doppler observations are then used to provide model inputs
at various points throughout the event. We find evidence that the wave mode
evolved from a mixture of fast and Alfvén modes at the beginning of the
event to an almost purely shear Alfvénic mode after 6 wavecycles (33 min). |
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