Modeling hiss spectrum and its dependence on source chorus and cold plasma density distribtion

Details Modeling hiss spectrum and its dependence on source chorus and cold plasma density distribtion Modeling hiss spectrum and its dependence on source chorus and cold plasma density distribtion

Dec 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufmsm13b2036c&link_type=abstract

American Geophysical Union, Fall Meeting 2011, abstract #SM13B-2036

Physics

[2768] Magnetospheric Physics / Plasmasphere, [2772] Magnetospheric Physics / Plasma Waves And Instabilities, [2774] Magnetospheric Physics / Radiation Belts

Scientific paper

There is increasing evidence that plasmaspheric hiss is formed by the evolution of a portion of chorus waves that are excited in the plasmatrough and propagate into the plasmasphere. We present a modeling study of the hiss spectrum, based on ray tracing, by taking chorus source as an input in the magnetosphere containing cold and suprathermal electrons. Our modeling results show that we are able to reproduce the main features of typical hiss, including frequency, wave normal angle and spatial distribution. However, simulated hiss intensity is weaker (~ 15 dB less) than observed intensity, which suggests internal amplification inside the plasmasphere. The response of the hiss spectrum to variation of the source chorus distribution is investigated. We find that the majority of the hiss-contributor chorus are those located within ~ 3 RE away from the plasmapause, wave normal direction pointing toward the Earth with wave normal angle 30-60 degrees, and over a frequency range of 0.1-0.3 fce. As chorus power increases closer to the plasmapause, the hiss intensity increases. We also investigate the response of hiss spectrum to the cold plasma density distribution. Our results show that hiss intensity near the field-aligned direction increases when the plasmasphere size decreases or the width of plasmapause layer increases, and the trough density distribution controls the amount of chorus power accessible to the plasmasphere. The slight increase in the trough density slope can enhance the hiss wave intensity by ~ 10 dB. Given the variability of chorus and cold plasma density, the resulting hiss intensity is still less than the observed values, which confirms that the formation of hiss is primarily due to the external chorus source and also needs additional internal amplification.

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