Poynting vector and wave vector directions of equatorial chorus

0472232 - ÚFA 2017 RIV US eng J - Journal Article
Taubenschuss, Ulrich - Santolík, Ondřej - Breuillard, H. - Li, W. - Le Contel, O.
Poynting vector and wave vector directions of equatorial chorus.
Journal of Geophysical Research-Space Physics. Roč. 121, č. 12 (2016), s. 11912-11928. ISSN 2169-9380. E-ISSN 2169-9402
R&D Projects: GA ČR(CZ) GA14-31899S; GA MŠMT(CZ) LH15304
Grant - others:AV ČR(CZ) AP1401
Program: Akademická prémie - Praemium Academiae
Institutional support: RVO:68378289
Keywords : whistler-mode waves * Earth's inner magnetosphere * Van Allen probes * plasmaspheric hiss * magnetic reconnection * outer magnetosphere * source region * emissions * propagation * THEMIS
Subject RIV: BL - Plasma and Gas Discharge Physics
Impact factor: 2.733, year: 2016

We present new results on wave vectors and Poynting vectors of chorus rising and falling tones on the basis of 6 years of THEMIS (Time History of Events and Macroscale Interactions during Substorms) observations. The majority of wave vectors is closely aligned with the direction of the ambient magnetic field (B-0). Oblique wave vectors are confined to the magnetic meridional plane, pointing away from Earth. Poynting vectors are found to be almost parallel to B-0. We show, for the first time, that slightly oblique Poynting vectors are directed away from Earth for rising tones and toward Earth for falling tones. For the majority of lower band chorus elements, the mutual orientation between Poynting vectors and wave vectors can be explained by whistler mode dispersion in a homogeneous collisionless cold plasma. Upper band chorus seems to require inclusion of collisional processes or taking into account azimuthal anisotropies in the propagation medium. The latitudinal extension of the equatorial source region can be limited to +/- 6 degrees around the B-0 minimum or approximately +/- 5000 km along magnetic field lines. We find increasing Poynting flux and focusing of Poynting vectors on the B-0 direction with increasing latitude. Also, wave vectors become most often more field aligned. A smaller group of chorus generated with very oblique wave normals tends to stay close to the whistler mode resonance cone. This suggests that close to the equatorial source region (within similar to 20 degrees latitude), a wave guidance mechanism is relevant, for example, in ducts of depleted or enhanced plasma density.
Permanent Link: http://hdl.handle.net/11104/0269652