Are equatorial electron cyclotron waves responsible for diffuse auroral electron precipitation?

Belmont, Gérard; Fontaine, Dominique; Canu, P.

doi:10.1029/ja088ia11p09163

Cited by 87 publications

(84 citation statements)

References 25 publications

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“…The alternative theory is electron scattering by whistler mode waves (Kennel et al, 1970;Lyons, 1974;Horne and Thorne, 2000). The main argument against the first theory has been that the power of the ECH waves measured at geostationary orbit is not sufficient to cause strong pitch angle diffusion (Belmont et al, 1983).The main problem with the second mechanism was that, although Johnstone et al (1993) showed that whistler mode waves can resonate with keV electrons in the frequency band below the electron gyro frequency, relatively high temperature anisotropies are required to generate such waves. Fig.…”

Section: Introductionmentioning

confidence: 99%

A study of fine structure of diffuse aurora with ALIS-FAST measurements

et al. 2008

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Abstract. We present results of an investigation of the fine structure of the night sector diffuse auroral zone, observed simultaneously with optical instruments (ALIS) from the ground and the FAST electron spectrometer from space 16 February 1997. Both the optical and particle data show that the diffuse auroral zone consisted of two regions. The equatorward part of the diffuse aurora was occupied by a pattern of regular, parallel auroral stripes. The auroral stripes were significantly brighter than the background luminosity, had widths of approximately 5 km and moved southward with a velocity of about 100 m/s. The second region, located between the region with auroral stripes and the discrete auroral arcs to the north, was filled with weak and almost homogeneous luminosity, against which short-lived auroral rays and small patches appeared chaotically. From analysis of the electron differential fluxes corresponding to the different regions of the diffuse aurora and based on existing theories of the scattering process we conclude the following: Strong pitch angle diffusion by electron cyclotron harmonic waves (ECH) of plasma sheet electrons in the energy range from a few hundred eV to 3-4 keV was responsible for the electron precipitation, that produced the background luminosity within the whole diffuse zone. The fine structure, represented by the auroral stripes, was created by precipitation of electrons above 3-4 keV as a result of pitch angle diffusion into the loss cone by whistler mode waves. A so called "internal gravity wave" (Safargaleev and Maltsev, 1986) may explain the formation of the regular spatial pattern formed by the auroral stripes in the equatorward part of the diffuse auroral zone.

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Section: Introductionmentioning

confidence: 99%

A study of fine structure of diffuse aurora with ALIS-FAST measurements

et al. 2008

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“…In the 1970s, the calculations of pitch angle scattering rate [Lyons,1974] based on the initial OGO-5 wave observations [Kennel et al, 1970] indicated that the amplitudes of ECH waves are large enough to scatter the electrons with energies from a few hundred eV to several keV, suggesting that the ECH waves are responsible for the loss of the plasma sheet electrons. However, in the 1980s, statistical surveys of occurrence rate of ECH waves indicated that the amplitude of ECH waves rarely have the sufficient power to scatter the plasma sheet electrons [e.g., Belmont et al, 1983;Roeder and Koons, 1989]. The new calculation of pitch angle diffusion done by Horne and Thorne [2000] suggested that the ECH waves can scatter the plasma sheet electrons when the waves lie the favored frequency ranges.…”

Section: Introductionmentioning

confidence: 99%

“…Thus, the wave-particle interactions are an important loss mechanism of the plasma sheet electrons. Both electron cyclotron harmonic (ECH) waves and the whistler mode chorus resonate with the plasma sheet electrons [Horne et al, 2003a], and the main contributor of the diffuse aurora (i.e., sweeper of the plasma sheet electrons) has been discussed by many researchers, but it is still a subject of controversy in magnetospheric physics [e.g., Belmont et al, 1983;Roeder and Koons, 1989;Horne and Thorne, 2000;Ni et al, 2008].…”

Section: Introductionmentioning

confidence: 99%

Transport and loss of the inner plasma sheet electrons: THEMIS observations

et al. 2011

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[1] Using the electron data from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft measurements from 2007 to 2009, we derived global phase space density (PSD) distributions of plasma sheet electrons (2-100 eV/nT) to examine the transport process of the electrons to the inner magnetosphere and possible loss mechanisms of plasma sheet electrons during the convective transport. The inner boundaries of the electron plasma sheet were determined by the observed global distributions and compared with the Alfvén boundaries that were calculated by the sum of the simple corotation and convection electric field models. This comparison confirms the previous results that the large-scale convection electric field controls the electron transport to the inner magnetosphere. The gradual decrease in PSD is observed from the dawn to the dayside sector, indicating the existence of some loss mechanisms in the morning sector. The loss time scales estimated from the PSD distributions were compared with the theoretical ones based on the quasi-linear diffusion theory using an empirical wave model of whistler mode chorus. We also estimated the required wave amplitudes that can explain the estimated loss time scales. It is shown that whistler mode chorus has a sufficient power to scatter the plasma sheet electrons, and the required wave amplitudes are roughly consistent with the CRRES statistical survey of the chorus wave amplitude. We suggest that the loss of plasma sheet electrons in the morning sector is mainly induced by pitch angle scattering by whistler mode chorus.

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“…Therefore, by studying the formation of pancakes, we may also be able to derive important information on the origin of the diffuse aurora., a problem which has been the subject of considerable controversy [e.g., Belmont et al, 1983Belmont et al, , 1984Lyons, 1984;Schumaker et al, 1989;Roeder and Koons, 1989] and which remains unresolved [Koskinnen, 1997].…”

Section: Introductionmentioning

confidence: 99%

Electron pitch angle diffusion by electrostatic electron cyclotron harmonic waves: The origin of pancake distributions

Horne¹,

Thorne²

2000

J. Geophys. Res.

129

191

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Abstract. It has been suggested that highly anisotropic electron pancake distributions are the result of pitch angle diffusion by electrostatic electron cyclotron harmonic (ECH) and whistler mode waves in the equatorial region. Here we present pitch angle diffusion rates for ECH wave spectra centered at different frequencies with respect to the electron gyrofrequency • corresponding to spacecraft observations. The wave spectra are carefully mapped to the correct resonant electron velocities. We show that previous diffusion calculations of ECH waves at 1.5•,, driven by the loss cone instability, result in large diffusion rates confined to a small range of pitch angles near the loss cone and therefore cannot account for pancake distributions. However, when the wave spectrum is centered at higher frequencies in the band (> 1.6•), the diffusion rates become very small inside the loss cone, pea,k just outside, and remain large over a wide range of pitch angles up to 60 ø or more. When the upper hybrid resonance frequency wuua is several times •, ECH waves excited in higher bands also contribute significantly to pitch a,ngle diffusion outside the loss cone up to very large pitch angles. We suggest that ECH waves driven by a loss cone could form pancake distributions as they grow if the wave spectrum extends from the middle to the upper part of the first (and higher) gyroharmonic bands. Alternatively, we suggest that pancake distributions can be formed by outward propagation in a nonhomogeneous medium, so that resonant absorption occurs at higher frequencies between (n + «) and (n + !)•qe in regions where waves are also growing locally at <_ 1.5•q•. The calculated diffusion rates suggest that ECH waves with amplitudes of the order of 1 mV m -t can form pancake distributions from an initially isotropic distribution on a timescale of a few hours. This is consistent with recent CRRES observations of ECH wave amplitudes following substorm injections near geostationary orbit and the timescales for pancake formation. Persistent but much weaker ECH waves can further intensify and maintain pancake distributions during magnetically quiet periods.

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Are equatorial electron cyclotron waves responsible for diffuse auroral electron precipitation?

Cited by 87 publications

References 25 publications

A study of fine structure of diffuse aurora with ALIS-FAST measurements

A study of fine structure of diffuse aurora with ALIS-FAST measurements

Transport and loss of the inner plasma sheet electrons: THEMIS observations

Electron pitch angle diffusion by electrostatic electron cyclotron harmonic waves: The origin of pancake distributions

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