Electron losses from the radiation belts caused by EMIC waves

Kersten, Tobias; Horne, Richard B.; Glauert, S. A.; Meredith, Nigel P.; Fraser, B. J.; Grew, R. S.

doi:10.1002/2014ja020366

Cited by 155 publications

(309 citation statements)

References 83 publications

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“…This value is consistent with the AMPTE survey results that the average power spectral density typically lies between 1 and 10 nT 2 /Hz [Anderson et al, 1992a[Anderson et al, , 1992b with a peak-to-peak wave amplitude of about 1.6 nT and between the CRRES survey results and the model results used by Kersten et al [2014]. Despite the differences, as long as the wave activity is not strong enough (<~2 nT) to trigger any nonlinear effect [e.g., Albert and Bortnik, 2009], quasi-linear bounce-averaged diffusion coefficients for different EMIC wave power can be easily obtained by scaling the results shown here by the square of wave amplitude.…”

Section: Discussionsupporting

confidence: 90%

“…For instance, Summers et al [2007] adopted 1% drift averaging for the considered three EMIC wave bands constantly; Li et al [2007] adopted 5% drift averaging during the storm main phase and 1% drift averaging during the storm recovery phase for the considered He + -band EMIC waves. Recently, Kersten et al [2014] adopted 25% drift averaging for the considered H + -band and He + -band EMIC waves, and Ma et al [2015] adopted 2% drift averaging for the considered He + -band EMIC waves. There is also recent evidence that the EMIC wavefield can extend over much larger MLT regions than previously believed,~12 h in local time or more [Engebretson et al, 2015], thus creating the possibility that the entire EMIC-driven scattering process described above could indeed take place over~1 min time scales, within a single drift orbit of the energetic electron population.…”

Section: Discussionmentioning

confidence: 99%

“…To model EMIC waves, we first assume that the three wave bands all follow a Gaussian frequency distribution, taking the form [e.g., Glauert and Horne, 2005;Meredith et al, 2014;Kersten et al, 2014] …”

Section: Model Descriptionmentioning

confidence: 99%

“…The wave normal distribution of EMIC waves is also assumed to be Gaussian and given by [e.g., Glauert and Horne, 2005;Ni et al, 2013Ni et al, , 2014aNi et al, , 2014bKersten et al, 2014] …”

Section: Model Descriptionmentioning

confidence: 99%

“…Compared to the other parameters, the wave normal angle information during the propagation of EMIC waves is difficult to acquire directly from in situ observations. Although EMIC waves are believed to become more and more oblique during their propagation to higher latitudes mainly due to the geomagnetic field gradient and curvature, previous studies have commonly adopted a parallel or quasi-parallel propagation assumption to determine the resonant scattering rates of EMIC waves [e.g., Summers and Thorne, 2003;Summers, 2005;Summers et al, 2007;Li et al, 2007;Ukhorskiy et al, 2010;Subbotin et al, 2010;Kersten et al, 2014;Ma et al, 2015]. The major purpose of this study is to evaluate the quantitative role of EMIC waves in driving scattering loss of outer radiation belt relativistic electrons and its sensitivity to wave normal angle distribution.…”

Section: Introductionmentioning

confidence: 99%

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Resonant scattering of outer zone relativistic electrons by multiband EMIC waves and resultant electron loss time scales

et al. 2015

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To improve our understanding of the role of electromagnetic ion cyclotron (EMIC) waves in radiation belt electron dynamics, we perform a comprehensive analysis of EMIC wave‐induced resonant scattering of outer zone relativistic (>0.5 MeV) electrons and resultant electron loss time scales with respect to EMIC wave band, L shell, and wave normal angle model. The results demonstrate that while H+‐band EMIC waves dominate the scattering losses of ~1–4 MeV outer zone relativistic electrons, it is He+‐band and O+‐band waves that prevail over the pitch angle diffusion of ultrarelativistic electrons at higher energies. Given the wave amplitude, EMIC waves at higher L shells tend to resonantly interact with a larger population of outer zone relativistic electrons and drive their pitch angle scattering more efficiently. Obliquity of EMIC waves can reduce the efficiency of wave‐induced relativistic electron pitch angle scattering. Compared to the frequently adopted parallel or quasi‐parallel model, use of the latitudinally varying wave normal angle model produces the largest decrease in H+‐band EMIC wave scattering rates at pitch angles < ~40° for electrons > ~5 MeV. At a representative nominal amplitude of 1 nT, EMIC wave scattering produces the equilibrium state (i.e., the lowest normal mode under which electrons at the same energy but different pitch angles decay exponentially on the same time scale) of outer belt relativistic electrons within several to tens of minutes and the following exponential decay extending to higher pitch angles on time scales from <1 min to ~1 h. The electron loss cone can be either empty as a result of the weak diffusion or heavily/fully filled due to approaching the strong diffusion limit, while the trapped electron population at high pitch angles close to 90° remains intact because of no resonant scattering. In this manner, EMIC wave scattering has the potential to deepen the anisotropic distribution of outer zone relativistic electrons by reshaping their pitch angle profiles to “top‐hat.” Overall, H+‐band and He+‐band EMIC waves are most efficient in producing the pitch angle scattering loss of relativistic electrons at ~1–2 MeV. In contrast, the presence of O+‐band EMIC waves, while at a smaller occurrence rate, can dominate the scattering loss of 5–10 MeV electrons in the entire region of the outer zone, which should be considered in future modeling of the outer zone relativistic electron dynamics.

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Section: Discussionsupporting

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Section: Model Descriptionmentioning

confidence: 99%

“…The wave normal distribution of EMIC waves is also assumed to be Gaussian and given by [e.g., Glauert and Horne, 2005;Ni et al, 2013Ni et al, , 2014aNi et al, , 2014bKersten et al, 2014] …”

Section: Model Descriptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Resonant scattering of outer zone relativistic electrons by multiband EMIC waves and resultant electron loss time scales

et al. 2015

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Modeling inward diffusion and slow decay of energetic electrons in the Earth's outer radiation belt

Thorne

et al. 2015

Geophysical Research Letters

103

135

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A new 3-D diffusion code is used to investigate the inward intrusion and slow decay of energetic radiation belt electrons (>0.5 MeV) observed by the Van Allen Probes during a 10 day quiet period on March 2013. During the inward transport, the peak differential electron fluxes decreased by approximately an order of magnitude at various energies. Our 3-D radiation belt simulation including radial diffusion and pitch angle and energy diffusion by plasmaspheric hiss and electromagnetic ion cyclotron (EMIC) waves reproduces the essential features of the observed electron flux evolution. The decay time scales and the pitch angle distributions in our simulation are consistent with the Van Allen Probe observations over multiple energy channels. Our study suggests that the quiet time energetic electron dynamics are effectively controlled by inward radial diffusion and pitch angle scattering due to a combination of plasmaspheric hiss and EMIC waves in the Earth's radiation belts.

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Estimation of pitch angle diffusion rates and precipitation time scales of electrons due to EMIC waves in a realistic field model

Kang

Fok

et al. 2015

JGR Space Physics

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Electromagnetic ion cyclotron (EMIC) waves are closely related to precipitating loss of relativistic electrons in the radiation belts, and thereby, a model of the radiation belts requires inclusion of the pitch angle diffusion caused by EMIC waves. We estimated the pitch angle diffusion rates and the corresponding precipitation time scales caused by H and He band EMIC waves using the Tsyganenko 04 (T04) magnetic field model at their probable regions in terms of geomagnetic conditions. The results correspond to enhanced pitch angle diffusion rates and reduced precipitation time scales compared to those based on the dipole model, up to several orders of magnitude for storm times. While both the plasma density and the magnetic field strength varied in these calculations, the reduction of the magnetic field strength predicted by the T04 model was found to be the main cause of the enhanced diffusion rates relative to those with the dipole model for the same Li values, where Li is defined from the ionospheric foot points of the field lines. We note that the bounce‐averaged diffusion rates were roughly proportional to the inversion of the equatorial magnetic field strength and thus suggest that scaling the diffusion rates with the magnetic field strength provides a good approximation to account for the effect of the realistic field model in the EMIC wave‐pitch angle diffusion modeling.

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Electron losses from the radiation belts caused by EMIC waves

Cited by 155 publications

References 83 publications

Resonant scattering of outer zone relativistic electrons by multiband EMIC waves and resultant electron loss time scales

Resonant scattering of outer zone relativistic electrons by multiband EMIC waves and resultant electron loss time scales

Modeling inward diffusion and slow decay of energetic electrons in the Earth's outer radiation belt

Estimation of pitch angle diffusion rates and precipitation time scales of electrons due to EMIC waves in a realistic field model

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