Magnetosonic waves above fc (H+) at geostationary orbit: GEOS 2 results

Laakso, H.; Junginger, H.; Roux, A.; Schmidt, Rudolf; Villedary, C. de

doi:10.1029/ja095ia07p10609

Cited by 77 publications

(73 citation statements)

References 21 publications

(17 reference statements)

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“…In fact, the wave particle interactions can play an important role in ring current, auroral, and plasma sheet dynamics. Particle data from Explorer 45, AMPTE/CCE, GEOS 1 and 2, and other spacecrafts clearly indicate the presence of hot nonthermal proton distributions in the ring current region (Fritz and Spjeldvik, 1979;Perraut et al, 1982;Kistler et al,' 1989;Laakso et al, 1990;Lui et al, 1990). Energetic ion distributions have been observed on the aurora1 field lines, in the cusp/cleft region and in the plasma sheet boundary layer (Hultqvist et al, 1988;Lundin and Eliasson, 1991;Daglis et al, 1993;Ghielmetti et al, 1978;Parks et al, 1984;Kistler et al, 1990;Peterson et al, 198 1).…”

Section: Introductionmentioning

confidence: 99%

Low-frequency electric field fluctuations excited by ring current protons

1996

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Energetic protons having ring type distributions are shown to generate low-frequency electrostatic waves, propagating nearly transverse to the geomagnetic field lines, in the ring current region by exciting Mode 1 and Mode 2 nonresonant instabilities and a resonant instability. Mode 1 nonresonant instability has frequencies around -4 Hz with transverse wavelengths of +%SO) km, and it is likely to occur in the region L = (7-8). Mode 2 nonresonant instability can generate frequencies +85&1450)Hz with transverse wavelengths ~(2-20) km. The typical frequencies and transverse wavelengths associated with the resonant instability are (950-1250) Hz and (3@65) km. Both the Mode 2 nonresonant instability and the resonant instability can occur in the ring current region with L = (46). The low-frequency modes driven by energetic protons could attain maximum saturation electric field amplitude varying from 0.8 mV/m to 70 mV/m. It is suggested that the turbulence produced by the low-frequency modes may cause pitch angle scattering of ring current protons in the region outside the plasmapause resulting in the ring current decay.

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Section: Introductionmentioning

confidence: 99%

Low-frequency electric field fluctuations excited by ring current protons

1996

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“…[Russell et al, 1970;Gumerr, 1976 Ray-tracing under the assumption that the waves propagate radially in the meridian plane shows that propagation effects can account for the characteristic "funnel" shape on frequency time spectrograms near the plasmapause [Boardsen et al, 1992]. However, while theoretical analysis shows tha.t the preferred propagation paths should be in the meridian pla.ne, analysis of electric field data at geostationary orbit shows that some of the wave emissions propagate azimuthally [Laakso et al, 1990]. Azimuthal propagation is possible provided the waves are refracted by a large density gradient such as the plasmapause [Kasahara et al, 1994].…”

Section: Introductionmentioning

confidence: 99%

Proton and electron heating by radially propagating fast magnetosonic waves

Horne¹,

Wheeler²,

Alleyne³

2000

J. Geophys. Res.

174

318

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Abstract. We investigate the propagation, growth, and decay of fast magnetosonic waves in the Earth's magnetosphere which are believed to contribute to proton heating up to energies of a few hundred eV near the magnetic equator. We construct a model of the proton and electron distribution functions from spacecraft data and use the HOTRAY code to calculate the path-integrated growth and decay of the waves over a range of L shells from L = 2 to L = 7. Instability calculations show that the waves are excited at very large angles of propagation with respect to the magnetic field, ;bm 89 ø, at the harmonics of the proton gyrofrequency up to the lower hybrid resonance frequency O$LH R by a proton ring distribution at energies of the order of 10 keV. As a "rule of thumb", we find that growth is possible for co > 30•qH+ when the ring velocity exceeds the Alfvdn speed and for co < 30[qH+ when v•t > 2v/i. For propagation in the meridian plane, waves generated just outside the plasmapause grow with large amplification as they propagate away from the Earth but eventually lose energy to plasma sheet electrons at energies of a few keV by Landau damping. The waves grow to large amplification at frequencies just below CVoeH•t. For inward propagation we find that waves generated just outside the plasmapause can propagate to L m 2 with very little attenuation, suggesting that waves observed well inside the plasmasphere could originate from a source region just outside the plasmapause. Strong wave growth only occurs for large angles of propagation, and thus the waves are confined to within a few degrees of the magnetic equator. Waves generated near geostationary orbit and which propagate toward the Earth are absorbed by Doppler-shifted cyclotron resonance when they propagate into a region where vR < va. Cyclotron resonant absorption causes pitch angle scattering and heating transverse to the ambient magnetic field. The amount of absorption, and hence transverse proton heating, increases significantly as the thermal proton temperature is increased up to 100 eV, suggesting a feedback process. Ray tracing shows that transverse heating of the thermal proton distribution is most likely to occur just outside the plasmapause where v•4 is large. Since proton ring distributions are formed during magnetic storms at ring current energies, we suggest that fast magnetosonic waves provide an additional energy loss process for ring current decay.

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“…Later observations (Gurnett, 1976;Perraut et al, 1982;Laakso et al, 1990;Kasahara et al, 1994;André et al, 2002) revealed that the equatorial noise occurs at radial distances between 2 and 7 R E , and at latitudes within 10 • from the magnetic equator, and that its lowest frequency could go down to the fundamental f H + . Detailed time-frequency spectrograms (Gurnett, 1976) also showed that, what appears as a noise band in the low resolution data, is in fact a superposition of many spectral lines with different frequency spacings.…”

Section: Introductionmentioning

confidence: 99%

Systematic analysis of equatorial noise below the lower hybrid frequency

et al. 2004

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Abstract.We report results of a systematic analysis of a large number of observations of equatorial noise between the local proton cyclotron frequency and the local lower hybrid frequency. The analysis is based on the data collected by the STAFF-SA instruments on board the four Cluster spacecraft. The data set covers their first two years of measurement in the equatorial magnetosphere at radial distances between 3.9 and 5 Earth radii. Inspection of 781 perigee passages shows that the occurrence rate of equatorial noise is approximately 60%. We identify equatorial noise by selecting data with nearly linearly polarized magnetic field fluctuations. These waves are found within 10 • of the geomagnetic equator, consistent with the published past observations. Our results show that equatorial noise has the most intense magnetic field fluctuations among all the natural emissions in the given interval of frequencies and latitudes. Electric field fluctuations of equatorial noise are also more intense compared to the average of all detected waves. Equatorial noise thus can play a non-negligible role in the dynamics of the internal magnetosphere.

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Magnetosonic waves above f_c (H⁺) at geostationary orbit: GEOS 2 results

Cited by 77 publications

References 21 publications

Low-frequency electric field fluctuations excited by ring current protons

Low-frequency electric field fluctuations excited by ring current protons

Proton and electron heating by radially propagating fast magnetosonic waves

Systematic analysis of equatorial noise below the lower hybrid frequency

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