Multipoint Observations of Equatorial Noise with a Quasiperiodic Modulation

0477972 - ÚFA 2018 BE eng A - Abstract
Němec, F. - Boardsen, S.A. - Santolík, Ondřej - Hospodarsky, G. B. - Pickett, J. S. - Cornilleau-Wehrlin, N. - Kurth, W. S. - Darrouzet, F. - Kletzing, C.
Multipoint Observations of Equatorial Noise with a Quasiperiodic Modulation.
Papers from URSI: XXXIInd General Assembly and Scientific Symposium (URSI GASS). Ghent: URSI, 2017. H41-2.
[URSI General Assembly and Scientific Symposium (URSI GASS) 2017 /32./. 19.08.2017-26.08.2017, Montreal]
Institutional support: RVO:68378289
Keywords : inner magnetosphere * waves in plasmas * Van Allen Probes * Cluster
Subject RIV: BL - Plasma and Gas Discharge Physics

Equatorial noise emissions are electromagnetic waves routinely observed in the equatorial region of the inner magnetosphere at frequencies between about the local proton cyclotron frequency and the lower hybrid frequency. They propagate nearly perpendicular to the ambient magnetic field, and they are believed to be generated by unstable ring-like proton distribution functions. High resolution data reveal that what appeared like a noise in low resolution frequency-time spectrograms is in fact a system of harmonic spectral lines corresponding to the proton cyclotron frequency in the source region. Until recently, these emissions were generally considered as continuous in time. However, in some cases, they exhibit a clear quasiperiodic modulation of the wave intensity. This quasiperiodic modulation of the wave intensity occurs in about 5 percent of the events, and it is observed predominantly during the daytime. We analyze a few hundreds of such events observed by the Cluster and Van Allen Probes spacecraft. Multicomponent wave measurements, allowing for a detailed wave analysis, are available on all these spacecraft. The intensity of the events is determined, and various factors affecting it are discussed. We further use the multipoint measurements to compare the exact timing of individual elements forming the events at various locations. Local plasma density measurements are used to determine the plasmapause location, which plays a crucial role in the event propagation. Finally, variations of the ambient magnetic field and of energetic proton distribution functions measured along with the events are investigated in order to identify a possible cause of the observed intensity modulation.
Permanent Link: http://hdl.handle.net/11104/0274211