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| Titel |
A study of L-dependent Pc3 pulsations observed by low Earth orbiting CHAMP satellite |
| VerfasserIn |
D. C. Ndiitwani, P. R. Sutcliffe |
| 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. 2 ; Nr. 28, no. 2 (2010-02-03), S.407-414 |
| Datensatznummer |
250016771
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| Publikation (Nr.) |
 copernicus.org/angeo-28-407-2010.pdf |
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| Zusammenfassung |
| Field line resonances (FLR) driven by compressional waves are an important
mechanism for the generation of ULF geomagnetic pulsations observed at all
latitudes during local daytime. References to observations of toroidal
standing Alfvén mode oscillations with clearly L-dependent frequencies
from spacecraft in the outer magnetosphere for L>3 are limited in the
literature. Such observations in the inner magnetosphere for L<3 have
not yet been reported in the literature. This study offers two interesting
case studies of observations of ULF waves by the low Earth orbiting CHAMP
satellite. The magnetic field measurements from CHAMP, which are of
unprecedented accuracy and resolution, are compared to Hermanus magnetometer
data for times when CHAMP crosses the ground station L-shell, namely for 13
February 2002 and 18 February 2003. The data were analysed for Pc3 pulsation
activity using the Maximum Entropy Spectral Analysis (MESA) method to
visualise FLRs in the vector magnetometer data. For the first time
observations of Pc3 toroidal oscillations with clearly L-dependent
frequencies for lower L-shell values (L<3) observed by an LEO satellite
are reported. These observations show FLR frequencies increasing as a
function of decreasing latitude down to L=1.6 and then decreasing as a
result of the larger plasma density of the upper ionosphere. The L-dependent
frequency oscillations were observed in the presence of a broadband
compressional wave spectrum. Our observations thus confirm the well-known
magnetohydrodynamic (MHD) wave theoretical prediction of a compressional
wave being the driver of the field line resonance. |
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