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| Titel |
The modulation of electromagnetic ion cyclotron waves by Pc 5 ULF waves |
| VerfasserIn |
T. M. Loto'aniu, B. J. Fraser, C. L. Waters |
| 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 ; 27, no. 1 ; Nr. 27, no. 1 (2009-01-07), S.121-130 |
| Datensatznummer |
250016361
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| Publikation (Nr.) |
 copernicus.org/angeo-27-121-2009.pdf |
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| Zusammenfassung |
| The modulation of electromagnetic ion cyclotron (EMIC) waves by longer-period
ULF waves has been proposed as a method for producing pearl structured Pc 1–2
EMIC waves. This study examines frequency and phase relationship between Pc 1
EMIC wavepacket envelopes and simultaneously occurring Pc 5 ULF waves using
magnetic data measured by the CRRES spacecraft. Intervals from three days in
1991 where CRRES observed pearls are presented along with simple statistics
for 58 EMIC wavepackets. The observations were dominated by EMIC waves
propagating away from the equatorial region. Comparisons between pearl
wavepacket envelopes and Pc 5 waves show excellent agreement. The pearl
wavepacket duration times, τdur, were statistically correlated with
Pc 5 wave periods, TPc5, resulting in a correlation coefficient of R=0.7
and best fit equation τdur=0.8·TPc5+6 s. In
general, phase differences varied although time intervals of constant
in-phase or anti-phase correlation were observed. Anti-phase modulation may
be explained by a decreasing background magnetic field due to the negative
cycle of the ULF wave decreasing Alfvén velocity and minimum resonant energy.
In-phase modulation could be the result of adiabatic modulation of
temperature anisotropy in-phase with variations in the background field.
Non-adiabatic processes may contribute to intervals that showed varying phase
differences with time. Results suggest that future theoretical developments
should take into account the full range of possible wave particle
interactions inside the magnetosphere. |
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