 |
| Titel |
Observations and modeling of forward and reflected chorus waves captured by THEMIS |
| VerfasserIn |
O. Agapitov, V. Krasnoselskikh, Yu. Zaliznyak, V. Angelopoulos, O. Contel, G. Rolland |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
0992-7689
|
| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 29, no. 3 ; Nr. 29, no. 3 (2011-03-11), S.541-550 |
| Datensatznummer |
250016990
|
| Publikation (Nr.) |
 copernicus.org/angeo-29-541-2011.pdf |
|
|
|
|
|
| Zusammenfassung |
| Discrete ELF/VLF chorus emissions are the most intense
electromagnetic plasma waves observed in the radiation belts of the Earth's
magnetosphere. Chorus emissions, whistler-mode wave packets propagating
roughly along magnetic field lines from a well-localized source in the
vicinity of the magnetic equator to polar regions, can be reflected at low
altitudes. After reflection, wave packets can return to the equatorial plane
region. Understanding of whistler wave propagation and reflection is critical
to a correct description of wave-particle interaction in the radiation belts.
We focus on properties of reflected chorus emissions observed by the THEMIS
(Time History of Events and Macroscale Interactions During Substorms)
spacecraft Search Coil Magnetometer (SCM) and Electric Field Instrument (EFI)
at ELF/VLF frequencies up to 4 kHz at L≥8. We determine the direction of
the Poynting flux and wave vector distribution for forward and reflected
chorus waves. Although both types of chorus waves were detected near the
magnetic equator and have similar, discrete structure and rising tones,
reflected waves are attenuated by a factor of 10–30 and have 10% higher
frequency than concurrently-observed forward waves. Modeling of wave
propagation and reflection using geometrical optics ray-tracing allowed us to
determine the chorus source region location and explain observed propagation
characteristics. We find that reflected wave attenuation at a certain spatial
region is caused by divergence of the ray paths of these non-ducted
emissions, and that the frequency shift is caused by generation of the
reflected waves at lower L-shells where the local equatorial gyrofrequency
is larger. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|