Physics
Scientific paper
Jul 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006jgra..11107302w&link_type=abstract
Journal of Geophysical Research, Volume 111, Issue A7, CiteID A07302
Physics
1
Ionosphere: Wave/Particle Interactions (7867), Ionosphere: Plasma Waves And Instabilities (2772), Ionosphere: Particle Precipitation, Magnetospheric Physics: Auroral Phenomena (2407), Magnetospheric Physics: Numerical Modeling
Scientific paper
Two recent papers report ground-based observations of ~3-30 Hz pulsations in the amplitude of 2fce auroral roar radio emissions. These pulsations occur in groups which last for ~1 s with adjacent pulsation groups spaced from one to several seconds. We put forth that these pulsations reflect periodic modulation of precipitating auroral electron fluxes, which could include periodic downward field-aligned bursts (FABs) and periodically modulated inverted-V electron precipitation, similar to those that could account for flickering aurora. We calculate time and frequency variations in the growth rate of Z-mode waves in the ionosphere for two different models of time-varying electron distribution functions, one corresponding to acceleration by electromagnetic ion cyclotron waves (EMIC) and the other corresponding to a simple time-varying accelerating potential (TVP). On the basis of these numerical calculations, the reported characteristics of ~10 Hz flickering roar appear consistent with modulations induced in the electron distribution function via interaction with EMIC waves, since the modulation associated with EMIC waves results in flickering of only the lower portion of the auroral roar frequency band, as in most of the observations. The few observed cases of higher-frequency flickering roar, at ~20-30 Hz, fall above the O+ cyclotron frequency for the altitude range on interest, and may represent a different source of electron flux modulation such as a varying electrostatic potential. The radio observations provide an additional means of probing flickering phenomenon and in particular may put constraints on the form of modulations of the electron distribution function at the auroral roar source height of a few hundred kilometers.
Hughes Janice M.
LaBelle James
Weatherwax Allan T.
Yoon Peter H.
Ziebell L. F.
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