Abstract
Abstract
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.
Department
Physics
Publication Date
8-2014
Journal Title
Geophysical Research Letters
Publisher
American Geophysical Union Publications
Digital Object Identifier (DOI)
10.1002/2014GL060628
Document Type
Article
Recommended Citation
Chen, L., et al. (2014), Generation of unusually low frequency plasmaspheric hiss, Geophys. Res. Lett., 41, 5702–5709, doi:10.1002/2014GL060628
Rights
©2014. American Geophysical Union.