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Generation of unusually low frequency plasmaspheric hiss
Author(s) -
Chen Lunjin,
Thorne Richard M.,
Bortnik Jacob,
Li Wen,
Horne Richard B.,
Reeves G. D.,
Kletzing C. A.,
Kurth W. S.,
Hospodarsky G. B.,
Spence H. E.,
Blake J. B.,
Fennell J. F.
Publication year - 2014
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2014gl060628
Subject(s) - hiss , plasmasphere , substorm , physics , van allen radiation belt , computational physics , infrasound , noise (video) , ray tracing (physics) , low frequency , geophysics , plasma , electron , optics , magnetosphere , acoustics , astronomy , nuclear physics , artificial intelligence , computer science , image (mathematics)
It has been reported from Van Allen Probe observations that plasmaspheric hiss intensification in the outer plasmasphere, associated with a substorm injection on 30 September 2012, occurred with a peak frequency near 100 Hz, well below the typical plasmaspheric hiss frequency range, extending down to ∼20 Hz. We examine this event of unusually low frequency plasmaspheric hiss to understand its generation mechanism. Quantitative analysis is performed by simulating wave raypaths via the HOTRAY ray tracing code with measured plasma density and calculating raypath‐integrated wave gain evaluated using the measured energetic electron distribution. We demonstrate that the growth rate due to substorm‐injected electrons is positive but rather weak, leading to small wave gain (∼10 dB) during a single equatorial crossing. Propagation characteristics aided by the sharp density gradient associated with the plasmapause, however, can enable these low‐frequency waves to undergo cyclic raypaths, which return to the unstable region leading to repeated amplification to yield sufficient net wave gain (>40 dB) to allow waves to grow from the thermal noise.