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| Titel |
On the numerical modelling of VLF chorus dynamical spectra |
| VerfasserIn |
D. Nunn, O. Santolík, M. Rycroft, V. Trakhtengerts |
| 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. 6 ; Nr. 27, no. 6 (2009-06-08), S.2341-2359 |
| Datensatznummer |
250016549
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| Publikation (Nr.) |
 copernicus.org/angeo-27-2341-2009.pdf |
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| Zusammenfassung |
| This paper presents a study of the use of a one-dimensional Vlasov Hybrid
Simulation (VHS) computer code to simulate the dynamical spectra (i.e.
frequency versus time spectrograms) of ELF/VLF chorus signals (from ~a fraction to ~10 kHz). Recently excellent measurements of chorus
have been made in the source region close to the geomagnetic equator aboard
the four spacecraft Cluster mission. Using Cluster data for wave amplitude,
which is up to 300 pT, local gyrofrequency, cold plasma density, and L-shell,
observed chorus signals are reproduced with remarkable fidelity and, in
particular, sweep rates in the range 1–10 kHz result as observed. Further, we
find that the sweep rate is a falling function of increasing cold plasma
density, again in accord with observations. Finally, we have satisfactorily
simulated the rather rare falling frequency elements of chorus which are
sometimes observed aboard Cluster in the generation region. For both rising
and falling chorus we have presented detailed structural analyses of the
generation regions. The main contributor to the frequency sweep rate is
primarily the establishment of wave number/frequency gradients across the
generation region by the out of phase component of the resonant particle
current. The secondary contributor is the shortening of the wavelength of
resonant particle current relative to that of the wave field. In view of the
close agreement between observation and simulation, we conclude that
nonlinear electron cyclotron resonance is indeed the mechanism underlying
the generation of chorus signals just outside the plasmasphere. |
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