Funnel‐shaped, low‐frequency equatorial waves

Boardsen, S. A.; Gallagher, D. L.; Gurnett, D. A.; Peterson, W. K.; Green, J. L.

doi:10.1029/92ja00827

Cited by 152 publications

(283 citation statements)

References 12 publications

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“…This type of frequency spectrum can be understood from the resonance condition and the shape of the distribution function. The growth rate is proportional to [Boardsen et al, 1992] …”

Section: Ray-tracing Modelmentioning

confidence: 99%

“…[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].…”

Section: Introductionmentioning

confidence: 99%

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Proton and electron heating by radially propagating fast magnetosonic waves

Horne¹,

Wheeler²,

Alleyne³

2000

J. Geophys. Res.

175

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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“…This type of frequency spectrum can be understood from the resonance condition and the shape of the distribution function. The growth rate is proportional to [Boardsen et al, 1992] …”

Section: Ray-tracing Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Proton and electron heating by radially propagating fast magnetosonic waves

Horne¹,

Wheeler²,

Alleyne³

2000

J. Geophys. Res.

175

318

View full text Add to dashboard Cite

show abstract

“…MS waves are believed to derive their energy from unstable "ring" distributions in the ion population [e.g., Gurnett, 1976;Perraut et al, 1982;Boardsen et al, 1992;Horne et al, 2000;Meredith et al, 2008;Xiao et al, 2013;Ma et al, 2014], which form mostly on the dayside as a result of the overlap of the westward drifting energetic ions (due to gradient curvature drift) and eastward drifting cold ions (due to the corotation electric field), with a null near ∼10 keV [e.g., Chen et al, 2010].…”

Section: Introductionmentioning

confidence: 99%

Analytical approximation of transit time scattering due to magnetosonic waves

Bortnik

Thorne

et al. 2015

Geophysical Research Letters

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Recent test particle simulations have shown that energetic electrons traveling through fast magnetosonic (MS) wave packets can experience an effect which is specifically associated with the tight equatorial confinement of these waves, known as transit time scattering. However, such test particle simulations can be computationally cumbersome and offer limited insight into the dominant physical processes controlling the wave-particle interactions, that is, in determining the effects of the various wave parameters and equatorial confinement on the particle scattering. In this paper, we show that such nonresonant effects can be effectively captured with a straightforward analytical treatment that is made possible with a set of reasonable, simplifying assumptions. It is shown that the effect of the wave confinement, which is not captured by the standard quasi-linear theory approach, acts in such a way as to broaden the range of particle energies and pitch angles that can effectively resonate with the wave. The resulting diffusion coefficients can be readily incorporated into global diffusion models in order to test the effects of transit time scattering on the dynamical evolution of radiation belt fluxes.

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“…Perraut et al [1982] identified them as magnetosonic waves, propagating in a direction almost perpendicular to B 0 , and suggested that the observed harmonic structure was related to nonlinear effects of locally generated waves rather than the superposition of multiple waves each generated at their local proton gyrofrequency. Boardsen et al [1992] and Horne et al [2000] modeled an instability that could be responsible for these waves using a "subtracted bi-Maxwellian" distribution function (with a population of lower T ? subtracted from a population with higher T ?…”

Section: Introductionmentioning

confidence: 99%

Multiple harmonic ULF waves in the plasma sheet boundary layer: Instability analysis

et al. 2010

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[1] Multiple-harmonic electromagnetic waves in the ULF band have occasionally been observed in Earth's magnetosphere, both near the magnetic equator in the outer plasmasphere and in the plasma sheet boundary layer (PSBL) in Earth's magnetotail. Observations by the Cluster spacecraft of multiple-harmonic electromagnetic waves with fundamental frequency near the local proton cyclotron frequency, W cp , were recently reported in the plasma sheet boundary layer by Broughton et al. (2008). A companion paper surveys the entire magnetotail passage of Cluster during 2003, and reports 35 such events, all in the PSBL, and all associated with elevated fluxes of counterstreaming ions and electrons. In this study we use observed pitch angle distributions of ions and electrons during a wave event observed by Cluster on 9 September 2003 to perform an instability analysis. We use a semiautomatic procedure for developing model distributions composed of bi-Maxwellian components that minimizes the difference between modeled and observed distribution functions. Analysis of wave instability using the WHAMP electromagnetic plasma wave dispersion code and these model distributions reveals an instability near W cp and its harmonics. The observed and model ion distributions exhibit both beam-like and ring-like features which might lead to instability. Further instability analysis with simple beam-like and ring-like model distribution functions indicates that the instability is due to the ring-like feature. Our analysis indicates that this instability persists over an enormous range in the effective ion beta (based on a best fit for the observed distribution function using a single Maxwellian distribution), b′, but that the character of the instability changes with b′. For b′ of order unity (for instance, the observed case with b′ ∼ 0.4), the instability is predominantly electromagnetic; the fluctuating magnetic field has components in both the perpendicular and parallel directions, but the perpendicular fluctuations are larger. If b′ is greatly decreased to about 5 × 10 −4 (by increasing the magnetic field), the instability becomes electrostatic. On the other hand, if b′ is increased (by decreasing the magnetic field), the instability remains electromagnetic, but becomes predominantly compressional (magnetic fluctuations predominantly parallel) at b′ ∼ 2. The b′ dependence we observe here may connect various waves at harmonics of the proton gyrofrequency found in different regions of space.

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Funnel‐shaped, low‐frequency equatorial waves

Cited by 152 publications

References 12 publications

Proton and electron heating by radially propagating fast magnetosonic waves

Proton and electron heating by radially propagating fast magnetosonic waves

Analytical approximation of transit time scattering due to magnetosonic waves

Multiple harmonic ULF waves in the plasma sheet boundary layer: Instability analysis

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