Quasiperiodic Whistler Mode Emissions Observed by the Van Allen Probes Spacecraft

0506364 - ÚFA 2020 RIV US eng J - Journal Article
Němec, F. - Hospodarsky, G. B. - Bezděková, B. - Demekhov, A. G. - Pasmanik, D. L. - Santolík, Ondřej - Kurth, W. S. - Hartley, D.
Quasiperiodic Whistler Mode Emissions Observed by the Van Allen Probes Spacecraft.
Journal of Geophysical Research-Space Physics. Roč. 123, č. 11 (2018), s. 8969-8982. ISSN 2169-9380. E-ISSN 2169-9402
Grant - others:AV ČR(CZ) AP1401
Program: Akademická prémie - Praemium Academiae
Institutional support: RVO:68378289
Keywords : ELF-VLF emissions * ELF/VLF wave emissions * magnetic pulsations * equatorial noise * longitudinal dependence * electron-precipitation * conjugate observations * cluster observations * modulation * magnetosphere
OECD category: Fluids and plasma physics (including surface physics)
Impact factor: 2.821, year: 2018
Method of publishing: Limited access
https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018JA026058

Quasiperiodic (QP) emissions are whistler mode electromagnetic waves observed in the inner magnetosphere that exhibit a QP time modulation of the wave intensity. We analyze 768 QP events observed during the first 5 years of the operation of the Van Allen Probes spacecraft (September 2012 to October 2017). Multicomponent wave measurements performed in the equatorial region, where the emissions are likely generated, are used to reveal new experimental information about their properties. We show that the events are observed nearly exclusively inside the plasmasphere. Wave frequencies are mostly between about 0.5 and 4 kHz. The events observed at larger radial distances and on the duskside tend to have slightly lower frequencies than the emissions observed elsewhere. The maximum event frequencies are limited by half of the equatorial electron gyrofrequency, suggesting the importance of wave ducting. Modulation periods are typically between about 0.5 and 5 min, and they increase with the in situ measured plasma number density. This increase is consistent with the main mechanisms suggested to explain the origin of the QP modulation. Two-point measurements performed by the Van Allen Probes are used to estimate a typical spatial extent of the emissions to about 1 R-E in radial distance and 1.5 hr in magnetic local time. Detailed wave analysis shows that the emissions are right-hand circularly polarized, and they usually come from several different directions simultaneously. They, however, predominantly propagate at rather low wave normal angles and away from the geomagnetic equator.
Permanent Link: http://hdl.handle.net/11104/0297618