期刊
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
卷 119, 期 11, 页码 8992-9003出版社
AMER GEOPHYSICAL UNION
DOI: 10.1002/2014JA020158
关键词
THEMIS; whistler mode waves; bandwidth; coherence coefficient; quasi-linear; nonlinear
资金
- NASA [NNX11AD75G, NNX11AR64G, NNX12AD12G, NNX13AI61G]
- NSF [AGS 1405054]
- National Science Foundation of China [41274124, 41274144]
- 973 Program [2012CB825602]
- German Ministry for Economy and Technology
- German Center for Aviation and Space (DLR) [50 OC 0302]
- Directorate For Geosciences [1405054] Funding Source: National Science Foundation
- Div Atmospheric & Geospace Sciences [1405054] Funding Source: National Science Foundation
- Div Atmospheric & Geospace Sciences
- Directorate For Geosciences [1405041] Funding Source: National Science Foundation
The bandwidths and coherence coefficients of lower band whistler mode waves are analyzed using Time History of Events and Macroscale Interactions during Substorms (THEMIS) waveform data for rising tones, falling tones, and hiss-like emissions separately. We also evaluate their dependences on the spatial location, electron density, the ratio of plasma frequency to local electron gyrofrequency (f(pe)/f(ce)), and the wave amplitude. Our results show that the bandwidth normalized by the local electron gyrofrequency (f(ce)) of rising and falling tones is very narrow (similar to 0.01 f(ce)), smaller than that of the hiss-like emissions (similar to 0.025 f(ce)). Meanwhile, the normalized bandwidth of discrete emissions gradually decreases with increasing wave amplitude, whereas that of hiss-like emissions increases slowly. The coherence coefficient of rising and falling tones is extremely large (similar to 1), while the coherence coefficient of hiss-like emissions is smaller but is still larger than 0.5. For all categories of whistler mode waves, the normalized bandwidth increases at larger L shells. Furthermore, the normalized bandwidth is positively correlated with local f(pe)/f(ce) but is inversely correlated with the electron density. Interactions between radiation belt electrons and whistler mode waves have been widely described by quasi-linear diffusion theory. Our results suggest that although quasi-linear theory is not entirely applicable for modeling electron interactions with rising and falling tones due to their narrow bandwidth and high coherence coefficient, it is suitable to treat wave-particle interactions between electrons and low-amplitude hiss-like emissions. Moreover, the correlations between the normalized bandwidth of chorus waves (especially the discrete emissions) and other parameters may provide insights for the generation mechanism of chorus waves.
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