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Equatorial Noise With Quasiperiodic Modulation: Multipoint Observations by the Van Allen Probes Spacecraft
Author(s) -
Němec F.,
Santolík O.,
Boardsen S. A.,
Hospodarsky G. B.,
Kurth W. S.
Publication year - 2018
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1029/2018ja025482
Subject(s) - plasmasphere , quasiperiodic function , spacecraft , physics , earth's magnetic field , noise (video) , modulation (music) , local time , equator , van allen probes , plasma , computational physics , geophysics , magnetosphere , van allen radiation belt , magnetic field , latitude , astronomy , condensed matter physics , statistics , mathematics , quantum mechanics , artificial intelligence , computer science , acoustics , image (mathematics)
Abstract Electromagnetic wave measurements performed by the two Van Allen Probes spacecraft are used to analyze equatorial noise emissions with a quasiperiodic modulation of the wave intensity. These waves are confined to the vicinity of the geomagnetic equator, and they occur primarily on the dayside. In situ plasma number density measurements are used to evaluate density variations related to the wave occurrence. It is shown that the events are sometimes effectively confined to low‐density regions, being observed at successive satellite passes over a time duration as long as 1 hr. The events typically occur outside the plasmasphere, and they often cease to exist just at the plasmapause. The analysis of the spatial separations of the spacecraft at the times when the events were observed simultaneously by both of them allows us to estimate the event spatial dimensions. It is found that the event spatial extent is typically lower than about 0.25 R E in radial distance and within about 1 hr in magnetic local time. Modulation periods of the events decrease with increasing plasma number density up to about 100 cm −3 . Principally no dependence is observed at larger densities, possibly indicating a propagation from other locations.