Physics
Scientific paper
Jun 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011jgra..11606206l&link_type=abstract
Journal of Geophysical Research, Volume 116, Issue A6, CiteID A06206
Physics
4
Ionosphere: Wave/Particle Interactions (7867), Ionosphere: Plasma Waves And Instabilities (2772), Magnetospheric Physics: Radiation Belts, Radio Science: Waves In Plasma (7867), Magnetospheric Physics: Magnetosphere: Inner
Scientific paper
Modulation of whistler mode chorus waves, which plays an important role in driving the pulsating aurora and other processes related to energetic electron dynamics, is an interesting but a long-standing unresolved problem. Here we utilize in situ observations from the THEMIS spacecraft to investigate the role of density variations in the modulation of the chorus wave amplitude, which forms a complementary study to the modulation of chorus by compressional Pc4-5 pulsations presented in a companion paper. We show that these density variations are correlated remarkably well with modulated chorus intensity and typically occur on a timescale of a few seconds to tens of seconds. Both density depletions (DD) and density enhancements (DE) are frequently correlated with increases in chorus wave amplitudes. Furthermore, density enhancements cause a lowering of the central frequencies of the generated chorus waves and vice versa. DD events are more likely to be related to quasi-periodic chorus emissions and thus may be related to the generation of the pulsating aurora. A systematic survey of both DD and DE events shows that DD events preferentially occur between premidnight and dawn, whereas DE events dominantly occur from dawn to noon. We also evaluate the growth rates of chorus waves using linear theory for both DD and DE events and show that both density depletions and enhancements can lead to an intensification of chorus wave growth. However, other potential mechanisms for chorus intensification caused by density variations such as wave trapping by density crests and troughs cannot be excluded.
Angelopoulos Vassilis
Bortnik Jacob
Chen Leon L.
Li Wangrong
Mansergh Thorne Richard
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