Magnetospheric chorus emissions: A review

Sazhin, Sergei; Hayakawa, Masashi

doi:10.1016/0032-0633(92)90009-d

Cited by 208 publications

(167 citation statements)

References 151 publications

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“…See also reviews by Omura et al (1991) and Sazhin and Hayakawa (1992) and references therein. Critical to radiation belt dynamics, these emissions have been studied intensively because they play a crucial role in the acceleration of energetic electrons at the outer radiation belt (Horne et al, 2005).…”

Section: Introductionmentioning

confidence: 99%

Observations and modeling of forward and reflected chorus waves captured by THEMIS

et al. 2011

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Abstract. Discrete ELF/VLF chorus emissions are the most intense electromagnetic plasma waves observed in the radiation belts of the Earth's magnetosphere. Chorus emissions, whistler-mode wave packets propagating roughly along magnetic field lines from a well-localized source in the vicinity of the magnetic equator to polar regions, can be reflected at low altitudes. After reflection, wave packets can return to the equatorial plane region. Understanding of whistler wave propagation and reflection is critical to a correct description of wave-particle interaction in the radiation belts. We focus on properties of reflected chorus emissions observed by the THEMIS (Time History of Events and Macroscale Interactions During Substorms) spacecraft Search Coil Magnetometer (SCM) and Electric Field Instrument (EFI) at ELF/VLF frequencies up to 4 kHz at L ≥ 8. We determine the direction of the Poynting flux and wave vector distribution for forward and reflected chorus waves. Although both types of chorus waves were detected near the magnetic equator and have similar, discrete structure and rising tones, reflected waves are attenuated by a factor of 10-30 and have 10% higher frequency than concurrently-observed forward waves. Modeling of wave propagation and reflection using geometrical optics ray-tracing allowed us to determine the chorus source region location and explain observed propagation characteristics. We find that reflected wave attenuation at a certain spatial region is caused by divergence of the ray paths of these non-ducted emissions, and that the frequency shift is caused by generation of the reflected waves at lower L-shells where the local equatorial gyrofrequency is larger.

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Section: Introductionmentioning

confidence: 99%

Observations and modeling of forward and reflected chorus waves captured by THEMIS

et al. 2011

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“…Saucers are often generated by upward moving field-aligned electrons in the return current region (Lönnqvist et al, 1993). Chorus seems to be generated by hot anisotropic electron distributions (Sazhin and Hayakawa, 1992). These waves all propagate on the whistler/lowerhybrid dispersion surface (André, 1985), on which we also find lower hybrid waves, though on this surface the latter waves should be confined to the lower hybrid plateau.…”

Section: Waves Around the Lower Hybrid Frequencymentioning

confidence: 68%

A statistical study of ion energization at 1700 km in the auroral region

et al. 2002

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Abstract. We present a comprehensive overview of several potentially relevant causes for the oxygen energization in the auroral region. Data from the Freja satellite near 1700 km altitude are used for an unconditional statistical investigation. The data are obtained in the Northern Hemisphere during 21 months in the declining phase of the solar cycle. The importance of various wave types for the ion energization is statistically studied. We also investigate the correlation of ion heating with precipitating protons, accelerated auroral electrons, suprathermal electron bursts, the electron density variations, K p index and solar illumination of the nearest conjugate ionosphere. We find that sufficiently strong broadband ELF waves, electromagnetic ion cyclotron waves, and waves around the lower hybrid frequency are foremost associated with the ion heating. However, magnetosonic waves, with a sharp, lower frequency cutoff just below the proton gyrofrequency, are not found to contribute to the ion heating. In the absence of the first three wave emissions, transversely energized ions are rare. These wave types are approximately equally efficient in heating the ions, but we find that the main source for the heating is broadband ELF waves, since they are most common in the auroral region. We have also observed that the conditions for ion heating are more favourable for smaller ratios of the spectral densities S E /S B of the broadband ELF waves at the oxygen gyrofrequency.

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“…Another noticeable difference between two studies would be the spectral-time structure of EMIC waves versus that of whistler waves. Chorus waves are characterized by a sequence of discrete elements appearing as intense short duration (typically 0.1 s) rising or, less often, falling tones in the frequency range from a few hundreds of hertz to several kilohertz [e.g., Omura et al, 1991;Sazhin and Hayakawa, 1992]. EMIC waves also appear as repeating discrete elements but not necessarily spaced as regularly as whistlers (see review by Fraser et al [2006]).…”

Section: Introductionmentioning

confidence: 99%

Characteristic dimension of electromagnetic ion cyclotron wave activity in the magnetosphere

2013

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[1] In this paper, we estimate the size of coherent activity of electromagnetic ion cyclotron (EMIC) waves using the multi-spacecraft observations made during the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission. We calculate the cross-correlations between EMIC wave powers measured by different THEMIS spacecraft, plot them over the separation distances between pairs of observing spacecraft, and determine the 1/e folding distance of the correlations as the characteristic dimension of the coherent wave activity. The characteristic radius in the direction transverse to the local magnetic field is found to lie in rather a wide range of 1500-8600 km varying from the AM to PM sectors and also from hydrogen to helium bands. However, the characteristic dimensions normalized by either gyroradius or wavelength fall into narrower ranges almost independent of the emission band and event location. Specifically, the coherent dimension is found to be 10-16 times gyroradius of 100 keV protons and 2-3 times local wavelength. The former may give a useful scale for the source dimension, and the latter suggests that the EMIC wave activity maintains coherency only up to a couple of wavelengths.

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Magnetospheric chorus emissions: A review

Cited by 208 publications

References 151 publications

Observations and modeling of forward and reflected chorus waves captured by THEMIS

Observations and modeling of forward and reflected chorus waves captured by THEMIS

A statistical study of ion energization at 1700 km in the auroral region

Characteristic dimension of electromagnetic ion cyclotron wave activity in the magnetosphere

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