Generation of unusually low frequency plasmaspheric hiss

Chen, Lunjin; Thorne, Richard M.; Bortnik, Jacob; Li, Wen; Horne, Richard B. ORCID:; Reeves, G. D.; Kletzing, C. A.; Kurth, W. S.; Hospodarsky, G. B.; Spence, H. E.; Blake, J. B.; Fennell, J. F.. 2014 Generation of unusually low frequency plasmaspheric hiss. Geophysical Research Letters, 41 (16). 5702-5709.

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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.

Item Type: Publication - Article
Digital Object Identifier (DOI):
Programmes: BAS Programmes > Polar Science for Planet Earth (2009 - ) > Climate
ISSN: 00948276
Additional Keywords: plasmaspheric hiss, ray tracing, chorus, generation
Date made live: 17 Nov 2014 11:52 +0 (UTC)

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