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| Titel |
Observations and modelling the wave mode evolution of an impulse-driven 3 mHz ULF wave. |
| VerfasserIn |
James Borderick, Tim Yeoman, Colin Waters, Darren Wright |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250031673
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| Zusammenfassung |
| Employing a combination of the Doppler Pulsation Experiment (DOPE), an HF doppler
sounder, in conjunction with the International Monitor for Auroral Geomagnetic Effects
(IMAGE) network of ground magnetometers, the Advanced Composition Explorer,
IMP-8 spacecraft and a numerical model we examine the evolution of a Ultra Low
Frequency (ULF) upstream wave from fast compressional to Alfvénic behavior.
The relative phases and amplitudes of the signatures in the doppler and ground
magnetometer data are compared with a numerical model for the generation of doppler
signatures from incident ULF waves. A one-dimensional model of wave propagation
from the magnetosphere, through the ionosphere to the ground with an oblique
magnetic field is employed. 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 HF radio path is calculated, and compared to observations. The event that
occurred on 16th April 1998 was the result of an impulsive disturbance as seen in
the ACE and IMP-8 spacecraft data and the IMF dynamic pressure increased at
approximately the right time and produced a low-m (-6) field line resonance with a large
characteristic scale size. Ground magnetic field and doppler observations were used to
find model inputs at various points throughout the event. We find evidence that
the wave mode evolved from a mixture of fast and Alfvén mode at the beginning
of the event to an almost purely Alfvénic mode after 6 wavecycles (33 minutes). |
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