| 1. |
- Fu, H. S., et al.
(författare)
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Discrete magnetosonic waves as an evidence of nonlinear wave-particle interaction
- 2014
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Ingår i: 2014 XXXITH URSI General Assembly And Scientific Symposium (URSI GASS). - 9781467352253
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Konferensbidrag (refereegranskat)abstract
- Two events, showing strong emissions near the lower hybrid frequency, are studied in detail in this paper. By analyzing the polarization degree, wave normal angle, and ellipticity, we conclude that the emissions are magnetosonic (MS) waves. These MS waves have opposite poynting fluxes in the radial and azimuthal direction, indicating that they were detected near the source region. In the wave spectrogram, discrete and "rising-tone" elements are found, suggesting that MS waves probably are a consequence of nonlinear wave-particle interaction.
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| 2. |
- Fu, H. S., et al.
(författare)
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First observation of rising-tone magnetosonic waves
- 2014
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 41:21, s. 7419-7426
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Tidskriftsartikel (refereegranskat)abstract
- Magnetosonic (MS) waves are linearly polarized emissions confined near the magnetic equator with wave normal angle near 90 degrees and frequency below the lower hybrid frequency. Such waves, also termed equatorial noise, were traditionally known to be "temporally continuous" in their time-frequency spectrogram. Here we show for the first time that MS waves actually have discrete wave elements with rising-tone features in their spectrogram. The frequency sweep rate of MS waves, similar to 1 Hz/s, is between that of chorus and electromagnetic ion cyclotron (EMIC) waves. For the two events we analyzed, MS waves occur outside the plasmapause and cannot penetrate into the plasmasphere; their power is smaller than that of chorus. We suggest that the rising-tone feature of MS waves is a consequence of nonlinear wave-particle interaction, as is the case with chorus and EMIC waves.
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| 3. |
- Taubenschuss, Ulrich, et al.
(författare)
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Different types of whistler mode chorus in the equatorial source region
- 2015
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:20, s. 8271-8279
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Tidskriftsartikel (refereegranskat)abstract
- The Time History of Events and Macroscale Interactions during Substorms-D spacecraft crossed an active equatorial source region of whistler mode chorus rising tones on 23 October 2008. Rising tones are analyzed in terms of spectral and polarization characteristics, with special emphasis on wave normal angles. The latter exhibit large variations from quasi-parallel to oblique, even within single bursts, but seem to follow a definite pattern, which enables an unambiguous classification into five different groups. Furthermore, we discuss the frequently observed splitting of chorus bursts into a lower and an upper band around one half of the local electron cyclotron frequency. At chorus frequencies close to the gap, we find significantly lowered wave planarities and a tendency of wave normal angles to approach the Gendrin angle.
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| 4. |
- Taubenschuss, Ulrich, et al.
(författare)
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Wave normal angles of whistler mode chorus rising and falling tones
- 2014
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 119:12
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Tidskriftsartikel (refereegranskat)abstract
- We present a study of wave normal angles (theta(k)) of whistler mode chorus emission as observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) during the year 2008. The three inner THEMIS satellites THA, THD, and THE usually orbit Earth close to the dipole magnetic equator (+/- 20 degrees), covering a large range of L shells from the plasmasphere out to the magnetopause. Waveform measurements of electric and magnetic fields enable a detailed polarization analysis of chorus below 4 kHz. When displayed in a frequency-theta(k) histogram, four characteristic regions of occurrence are evident. They are separated by gaps at f/f(c,e) approximate to 0.5 (f is the chorus frequency, f(c,e) is the local electron cyclotron frequency) and at theta(k) similar to 40 degrees. Below theta(k) similar to 40 degrees, the average value for theta(k) is predominantly field aligned, but slightly increasing with frequency toward half of f(c,e) (theta(k) up to 20 degrees). Above half of f(c,e), the average theta(k) is again decreasing with frequency. Above theta(k) similar to 40 degrees, wave normal angles are usually close to the resonance cone angle. Furthermore, we present a detailed comparison of electric and magnetic fields of chorus rising and falling tones. Falling tones exhibit peaks in occurrence solely for theta(k) > 40 degrees and are propagating close to the resonance cone angle. Nevertheless, when comparing rising tones to falling tones at theta(k) > 40 degrees, the ratio of magnetic to electric field shows no significant differences. Thus, we conclude that falling tones are generated under similar conditions as rising tones, with common source regions close to the magnetic equatorial plane.
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