Coherently modulated whistler mode waves simultaneously observed over unexpectedly large spatial scales

TitleCoherently modulated whistler mode waves simultaneously observed over unexpectedly large spatial scales
Publication TypeJournal Article
Year of Publication2017
AuthorsLi, J, Bortnik, J, Li, W, Thorne, RM, Ma, Q, Chu, X, Chen, L, Kletzing, CA, Kurth, WS, Hospodarsky, GB, Wygant, J, Breneman, A, Thaller, S
JournalJournal of Geophysical Research: Space Physics
Date Published02/2017
Keywordscoherent waves; multisatellite; periodic rising tone; Van Allen Probes; whistler mode
AbstractUtilizing simultaneous twin Van Allen Probes observations of whistler mode waves at variable separations, we are able to distinguish the temporal variations from spatial variations, determine the coherence spatial scale, and suggest the possible mechanism of wave modulation. The two probes observed coherently modulated whistler mode waves simultaneously at an unexpectedly large distance up to ~4.3 RE over 3 h during a relatively quiet period. The modulation of 150–500 Hz plasmaspheric hiss was correlated with whistler mode waves measured outside the plasmasphere across 3 h in magnetic local time and 3 L shells, revealing that the modulation was temporal in nature. We suggest that the coherent modulation of whistler mode waves was associated with the coherent ULF waves measured over a large scale, which modulate the plasmaspheric density and result in the modulation of hiss waves via local amplification. In a later period, the 500–1500 Hz periodic rising-tone whistler mode waves were strongly correlated when the two probes traversed large spatial regions and even across the plasmapause. These periodic rising-tone emissions recurred with roughly the same period as the ULF wave, but there was no one-to-one correspondence, and a cross-correlation analysis suggests that they possibly originated from large L shells although the actual cause needs further investigation.

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