Journal
JOURNAL OF GEOPHYSICAL RESEARCH-SPACE PHYSICS
Volume 116, Issue -, Pages -Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1029/2011JA017035
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Funding
- NASA [NNX11AD75G, NNX08AI35G, NAS5-02099]
- NSF [AGS-0840178]
- German Ministry for Economy and Technology
- German Center for Aviation and Space (DLR) [50 OC 0302]
- NASA [100787, NNX08AI35G] Funding Source: Federal RePORTER
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The global distribution of chorus wave amplitudes and their wave normal angles is investigated using high-resolution wave spectra and waveform data from THEMIS for lower-band and upper-band chorus separately. Statistical results show that large amplitude chorus (>300 pT) occurs predominantly from premidnight to postdawn and is preferentially observed at lower L shells (<8) near the magnetic equator. However, strong or moderate chorus extends further into the afternoon sector and to higher L shells. For lower-band chorus, strong waves (>50 pT) tend to have wave normal angles of <20 degrees and their wave normal angles become even smaller with increasing wave amplitudes. For modest waves, the wave normal angles are distributed over a broad range with a major peak at <20 degrees and a secondary peak at 60 degrees-80 degrees. Wave normal angles of lower-band chorus are generally smaller on the dayside than on the nightside possibly due to the more uniform and more compressed magnetic field configuration on the dayside. Lower-band chorus becomes more oblique with increasing latitude on the dayside, whereas on the nightside the probability of observing oblique chorus decreases at higher latitudes. Compared to lower-band chorus, the properties of upper-band chorus are somewhat different. Upper-band chorus is considerably weaker in magnetic wave amplitudes, shows tighter confinement to the magnetic equator (<10 degrees), and occurs at smaller L shells (<8). Furthermore, wave normal angles of upper-band chorus are generally larger than those of lower-band chorus, but the occurrence rate still peaks at wave normal angles of < 20 degrees, particularly for strong upper-band chorus.
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