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Yuri Shprits - One of the best experts on this subject based on the ideXlab platform.
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hot plasma effects on the cyclotron resonant Pitch Angle scattering rates of radiation belt electrons due to emic waves
Geophysical Research Letters, 2018Co-Authors: Binbin Ni, Yuri Shprits, Xudong Gu, Danny Summers, Song FuAbstract:To investigate the hot plasma effects on the cyclotron-resonant interactions between electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons in a realistic magnetospheric environment, calculations of the wave-induced bounce-averaged Pitch Angle diffusion coefficients are performed using both the cold and hot plasma dispersion relations. The results demonstrate that the hot plasma effects have a pronounced influence on the electron Pitch Angle scattering rates due to all three EMIC emission bands (H+, He+, and O+) when the hot plasma dispersion relation deviates significantly from the cold plasma approximation. For a given wave spectrum, the modification of the dispersion relation by hot anisotropic protons can strongly increase the minimum resonant energy for electrons interacting with O+ band EMIC waves, while the minimum resonant energies for H+ and He+ bands are not greatly affected. For H+ band EMIC waves, inclusion of hot protons tends to weaken the Pitch Angle scattering efficiency of >5 MeV electrons. The most crucial differences introduced by the hot plasma effects occur for >3 MeV electron scattering rates by He+ band EMIC waves. Mainly due to the changes of resonant frequency and wave group velocity when the hot protons are included, the difference in scattering rates can be up to an order of magnitude, showing a strong dependence on both electron energy and equatorial Pitch Angle. Our study confirms the importance of including hot plasma effects in modeling the scattering of ultra-relativistic radiation belt electrons by EMIC waves.
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hot plasma effects on the cyclotron resonant Pitch Angle scattering rates of radiation belt electrons due to emic waves
Geophysical Research Letters, 2018Co-Authors: Binbin Ni, Yuri Shprits, Xudong Gu, Danny Summers, Song FuAbstract:To investigate the hot plasma effects on the cyclotron-resonant interactions between electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons in a realistic magnetospheric environment, calculations of the wave-induced bounce-averaged Pitch Angle diffusion coefficients are performed using both the cold and hot plasma dispersion relations. The results demonstrate that the hot plasma effects have a pronounced influence on the electron Pitch Angle scattering rates due to all three EMIC emission bands (H+, He+, and O+) when the hot plasma dispersion relation deviates significantly from the cold plasma approximation. For a given wave spectrum, the modification of the dispersion relation by hot anisotropic protons can strongly increase the minimum resonant energy for electrons interacting with O+ band EMIC waves, while the minimum resonant energies for H+ and He+ bands are not greatly affected. For H+ band EMIC waves, inclusion of hot protons tends to weaken the Pitch Angle scattering efficiency of >5 MeV electrons. The most crucial differences introduced by the hot plasma effects occur for >3 MeV electron scattering rates by He+ band EMIC waves. Mainly due to the changes of resonant frequency and wave group velocity when the hot protons are included, the difference in scattering rates can be up to an order of magnitude, showing a strong dependence on both electron energy and equatorial Pitch Angle. Our study confirms the importance of including hot plasma effects in modeling the scattering of ultra-relativistic radiation belt electrons by EMIC waves.
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understanding the dynamic evolution of the relativistic electron slot region including radial and Pitch Angle diffusion
Journal of Geophysical Research, 2011Co-Authors: Yuri Shprits, D Subbotin, Binbin NiAbstract:[1] It has been suggested that the equilibrium structure of the slot region, which separates the inner and outer radiation belts, forms as the result of a balance between inward radial diffusion and Pitch Angle scattering of relativistic electrons by interactions with three types of whistler mode waves: plasmaspheric hiss, lightening-generated whistlers, and ground-based Very Low Frequency (VLF) transmitters. In this study, using the time-dependent 3D Versatile Electron Radiation Belt (VERB) code, we examine how effectively the slot can be formed by a combination of radial diffusion and Pitch Angle diffusion, together with Coulomb scattering, and compare the simulations with the CRRES MEA 1 MeV electron observations to examine the viability of the various scattering mechanisms. The results show that the overall time evolution of the observed two-zone structure is in a good agreement with our model simulations, which suggests a balance between inward radial diffusion due to Ultra Low Frequency (ULF) electromagnetic fluctuations and Pitch Angle scattering due to plasmaspheric hiss and lightning-generated whistlers. However, when inward radial diffusion due to the electrostatic fluctuations is included, agreement between the observed and simulated fluxes becomes weaker, suggesting that it is important to understand and quantify the radial diffusion rates in the slot region.
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statistical analysis of Pitch Angle distribution of radiation belt energetic electrons near the geostationary orbit crres observations
Journal of Geophysical Research, 2011Co-Authors: Xudong Gu, Yuri Shprits, Binbin Ni, Zhengyu Zhao, Chen ZhouAbstract:[1] A statistical analysis of energetic radiation belt electron Pitch Angle distributions (PADs) at the radial distances of 6 RE and 6.6 RE is performed on the basis of the Pitch Angle resolved flux observations from the Medium Electrons A (MEA) instrument onboard the Combined Release and Radiation Effects Satellite (CRRES). While previous studies of Vampola (1998) and Gannon et al. (2007) have used CRRES MEA data to investigate the general variations in electron PAD at particular energies, in this study we present a detailed statistical analysis of electron PADs including the dependence on electron kinetic energy, magnetic local time (MLT), and the level of geomagnetic activity. By fitting the measured PADs with a power law function of sine of local Pitch Angle, the power law index n that relates to the category of radiation belt electron PAD is quantified in detail as a function of electron kinetic energy, MLT interval, and geomagnetic index Kp. Statistical averaged n values vary considerably with respect to MLT, ranging from n ∼ 0 within 0000–0400 MLT to n ∼ 1.5 within 1200–1600 MLT, because of the MLT dependence of wave scattering and the effects associated with drift shell splitting and magnetopause shadowing. Drift shell splitting and magnetopause shadowing result in often observed negative values of n. At lower energies of a few hundred keV the Pitch Angle distributions are more flat than at MeV energies, which is consistent with faster Pitch Angle scattering at low energies by chorus waves. These quantitative results of radiation belt electron PAD, consistent with the previous studies by Vampola (1998) and Gannon et al. (2007), provide further insight into the global dynamics of energetic radiation belt electrons near the geostationary orbit and also are useful for inferring electron phase space densities and assimilating their radial profiles using omnidirectional electron flux measurements.
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estimates of lifetimes against Pitch Angle diffusion
Journal of Atmospheric and Solar-Terrestrial Physics, 2009Co-Authors: J M Albert, Yuri ShpritsAbstract:Abstract We consider timescales on which particle distributions respond to Pitch Angle diffusion. On the longest timescale, the distribution decays at a single rate independent of equatorial Pitch Angle α 0 , even though the diffusion coefficient, and the distribution itself, may vary greatly with α 0 . We derive a simple integral expression to approximate this decay rate and show that it gives good agreement with the full expression. The roles of both the minimum and loss cone values of the diffusion coefficient are demonstrated and clarified.
R M Thorne - One of the best experts on this subject based on the ideXlab platform.
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variability of the Pitch Angle distribution of radiation belt ultrarelativistic electrons during and following intense geomagnetic storms van allen probes observations
Journal of Geophysical Research, 2015Co-Authors: Zhengyang Zou, R M Thorne, H E Spence, Zhengyu Zhao, Chen Zhou, J Bortnik, Run Shi, D N Baker, Shrikhanth G Kanekal, G D ReevesAbstract:Fifteen months of Pitch Angle resolved Van Allen Probes Relativistic Electron-Proton Telescope (REPT) measurements of differential electron flux are analyzed to investigate the characteristic variability of the Pitch Angle distribution of radiation belt ultrarelativistic (>2MeV) electrons during storm conditions and during the long-term poststorm decay. By modeling the ultrarelativistic electron Pitch Angle distribution as sin(n)alpha, where alpha is the equatorial Pitch Angle, we examine the spatiotemporal variations of the n value. The results show that, in general, n values increase with the level of geomagnetic activity. In principle, ultrarelativistic electrons respond to geomagnetic storms by becoming more peaked at 90 degrees Pitch Angle with n values of 2-3 as a supportive signature of chorus acceleration outside the plasmasphere. High n values also exist inside the plasmasphere, being localized adjacent to the plasmapause and exhibiting energy dependence, which suggests a significant contribution from electromagnetic ion cyclotron (EMIC) wave scattering. During quiet periods, n values generally evolve to become small, i.e., 0-1. The slow and long-term decays of the ultrarelativistic electrons after geomagnetic storms, while prominent, produce energy and L-shell-dependent decay time scales in association with the solar and geomagnetic activity and wave-particle interaction processes. At lower L shells inside the plasmasphere, the decay time scales tau(d) for electrons at REPT energies are generally larger, varying from tens of days to hundreds of days, which can be mainly attributed to the combined effect of hiss-induced Pitch Angle scattering and inward radial diffusion. As L shell increases to L similar to 3.5, a narrow region exists (with a width of similar to 0.5L), where the observed ultrarelativistic electrons decay fastest, possibly resulting from efficient EMIC wave scattering. As L shell continues to increase, tau(d) generally becomes larger again, indicating an overall slower loss process by waves at high L shells. Our investigation based upon the sin(n)alpha function fitting and the estimate of decay time scale offers a convenient and useful means to evaluate the underlying physical processes that play a role in driving the acceleration and loss of ultrarelativistic electrons and to assess their relative contributions.
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resonant scattering and resultant Pitch Angle evolution of relativistic electrons by plasmaspheric hiss
AGU Fall Meeting Abstracts, 2013Co-Authors: J Bortnik, R M Thorne, Lunjin ChenAbstract:[1] We perform a comprehensive analysis to evaluate hiss-induced scattering effect on the Pitch Angle evolution and associated decay processes of relativistic electrons. The results show that scattering by the equatorial, highly oblique hiss component is negligible. Quasi-parallel approximation is good for evaluation of hiss-driven electron scattering rates ≤ 2 MeV. However, realistic wave propagation Angles as a function of latitude must be considered to accurately quantify hiss scattering rates above 2 MeV, and ambient plasma density is also a critical parameter. While the first-order cyclotron and the Landau resonances are dominant for hiss scattering 100 days for 500 keV, 2 MeV, and 5 MeV electrons, respectively, consistent with recent observations from the Van Allen Probes and indicating that scattering by hiss can realistically account for the long-term loss process and the Pitch Angle evolution of relativistic electrons in the plasmasphere following storm time injections.
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evolution of electron Pitch Angle distributions following injection from the plasma sheet
Journal of Geophysical Research, 2011Co-Authors: Xin Tao, R M Thorne, Nigel P Meredith, Richard B HorneAbstract:[1] The temporal evolution of the phase space density of plasma sheet electrons (100 eV–30 keV) injected into the nightside at L = 6 during moderate geomagnetic activity is investigated using a quasi-linear diffusion formulation. Scattering in energy and Pitch Angle during interactions with both whistler mode chorus waves and electron cyclotron harmonic waves are included using an improved wave model recently obtained using CRRES spacecraft data. We compare our simulation results with observations from the THEMIS spacecraft and demonstrate that the formation of the observed electron Pitch Angle distributions is mainly due to resonant interactions with a combination of upper and lower band chorus waves. The pancake distributions at low energies (E 3 keV) are explained using the banded chorus wave structure with a power minimum at half the electron cyclotron frequency. Results of the current work can be used to model the dynamical evolution and resultant global distribution of plasma sheet electrons.
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simulations of Pitch Angle scattering of relativistic electrons with mlt dependent diffusion coefficients
Journal of Geophysical Research, 2009Co-Authors: Yuri Shprits, Lunjin Chen, R M ThorneAbstract:[1] We present magnetic local time (MLT)-dependent simulations of Pitch Angle scattering of relativistic (approximately MeV) electrons by chorus and electromagnetic ion cyclotron (EMIC) waves. Numerical simulations indicate that in the case of scattering by chorus waves, the Pitch Angle distribution is relatively independent of MLT. In the case of scattering by EMIC and chorus waves, the modeled Pitch Angle distribution shows significant variations with MLT. MLT-averaged simulations tend to overestimate net loss during a storm but can accurately predict equilibrium loss rates and the overall shape of the Pitch Angle distribution. Numerical simulations show that EMIC waves not only scatter electrons into the loss cone but also create gradients in the Pitch Angle distribution, assisting chorus waves in scattering relativistic electrons into the loss cone. We also show that changes in the spectral properties of waves can significantly change loss rates. Loss rates reach a maximum level for EMIC waves with amplitudes above approximately 1 nT, present over a few percent of the drift orbit, and then become relatively independent of the amplitudes of EMIC waves.
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controlling effect of the Pitch Angle scattering rates near the edge of the loss cone on electron lifetimes
Journal of Geophysical Research, 2006Co-Authors: Yuri Shprits, W Li, R M ThorneAbstract:[1] Intense interest currently exists in quantification of the loss of relativistic electrons in the outer radiation belts. Using diffusion coefficients computed for parallel propagating chorus waves, the evolution of the electron Pitch Angle distribution is examined. Sensitivity numerical experiments show that electron lifetimes are most sensitive to the value of the Pitch Angle scattering rate near the edge of the loss cone. When the scattering rates do not drop by more than an order of magnitude of the value near the edge of the loss cone for a 30 degree range of Pitch Angles, we find that the Pitch Angle distribution reaches an equilibrium shape within hours of the simulations and then decays exponentially with the same rate at all equatorial Pitch Angles. Implications of the results for combined scattering by EMIC and chorus or hiss waves are discussed as well as implications for future modeling and comparison with observations.
Binbin Ni - One of the best experts on this subject based on the ideXlab platform.
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hot plasma effects on the cyclotron resonant Pitch Angle scattering rates of radiation belt electrons due to emic waves
Geophysical Research Letters, 2018Co-Authors: Binbin Ni, Yuri Shprits, Xudong Gu, Danny Summers, Song FuAbstract:To investigate the hot plasma effects on the cyclotron-resonant interactions between electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons in a realistic magnetospheric environment, calculations of the wave-induced bounce-averaged Pitch Angle diffusion coefficients are performed using both the cold and hot plasma dispersion relations. The results demonstrate that the hot plasma effects have a pronounced influence on the electron Pitch Angle scattering rates due to all three EMIC emission bands (H+, He+, and O+) when the hot plasma dispersion relation deviates significantly from the cold plasma approximation. For a given wave spectrum, the modification of the dispersion relation by hot anisotropic protons can strongly increase the minimum resonant energy for electrons interacting with O+ band EMIC waves, while the minimum resonant energies for H+ and He+ bands are not greatly affected. For H+ band EMIC waves, inclusion of hot protons tends to weaken the Pitch Angle scattering efficiency of >5 MeV electrons. The most crucial differences introduced by the hot plasma effects occur for >3 MeV electron scattering rates by He+ band EMIC waves. Mainly due to the changes of resonant frequency and wave group velocity when the hot protons are included, the difference in scattering rates can be up to an order of magnitude, showing a strong dependence on both electron energy and equatorial Pitch Angle. Our study confirms the importance of including hot plasma effects in modeling the scattering of ultra-relativistic radiation belt electrons by EMIC waves.
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hot plasma effects on the cyclotron resonant Pitch Angle scattering rates of radiation belt electrons due to emic waves
Geophysical Research Letters, 2018Co-Authors: Binbin Ni, Yuri Shprits, Xudong Gu, Danny Summers, Song FuAbstract:To investigate the hot plasma effects on the cyclotron-resonant interactions between electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons in a realistic magnetospheric environment, calculations of the wave-induced bounce-averaged Pitch Angle diffusion coefficients are performed using both the cold and hot plasma dispersion relations. The results demonstrate that the hot plasma effects have a pronounced influence on the electron Pitch Angle scattering rates due to all three EMIC emission bands (H+, He+, and O+) when the hot plasma dispersion relation deviates significantly from the cold plasma approximation. For a given wave spectrum, the modification of the dispersion relation by hot anisotropic protons can strongly increase the minimum resonant energy for electrons interacting with O+ band EMIC waves, while the minimum resonant energies for H+ and He+ bands are not greatly affected. For H+ band EMIC waves, inclusion of hot protons tends to weaken the Pitch Angle scattering efficiency of >5 MeV electrons. The most crucial differences introduced by the hot plasma effects occur for >3 MeV electron scattering rates by He+ band EMIC waves. Mainly due to the changes of resonant frequency and wave group velocity when the hot protons are included, the difference in scattering rates can be up to an order of magnitude, showing a strong dependence on both electron energy and equatorial Pitch Angle. Our study confirms the importance of including hot plasma effects in modeling the scattering of ultra-relativistic radiation belt electrons by EMIC waves.
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understanding the dynamic evolution of the relativistic electron slot region including radial and Pitch Angle diffusion
Journal of Geophysical Research, 2011Co-Authors: Yuri Shprits, D Subbotin, Binbin NiAbstract:[1] It has been suggested that the equilibrium structure of the slot region, which separates the inner and outer radiation belts, forms as the result of a balance between inward radial diffusion and Pitch Angle scattering of relativistic electrons by interactions with three types of whistler mode waves: plasmaspheric hiss, lightening-generated whistlers, and ground-based Very Low Frequency (VLF) transmitters. In this study, using the time-dependent 3D Versatile Electron Radiation Belt (VERB) code, we examine how effectively the slot can be formed by a combination of radial diffusion and Pitch Angle diffusion, together with Coulomb scattering, and compare the simulations with the CRRES MEA 1 MeV electron observations to examine the viability of the various scattering mechanisms. The results show that the overall time evolution of the observed two-zone structure is in a good agreement with our model simulations, which suggests a balance between inward radial diffusion due to Ultra Low Frequency (ULF) electromagnetic fluctuations and Pitch Angle scattering due to plasmaspheric hiss and lightning-generated whistlers. However, when inward radial diffusion due to the electrostatic fluctuations is included, agreement between the observed and simulated fluxes becomes weaker, suggesting that it is important to understand and quantify the radial diffusion rates in the slot region.
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statistical analysis of Pitch Angle distribution of radiation belt energetic electrons near the geostationary orbit crres observations
Journal of Geophysical Research, 2011Co-Authors: Xudong Gu, Yuri Shprits, Binbin Ni, Zhengyu Zhao, Chen ZhouAbstract:[1] A statistical analysis of energetic radiation belt electron Pitch Angle distributions (PADs) at the radial distances of 6 RE and 6.6 RE is performed on the basis of the Pitch Angle resolved flux observations from the Medium Electrons A (MEA) instrument onboard the Combined Release and Radiation Effects Satellite (CRRES). While previous studies of Vampola (1998) and Gannon et al. (2007) have used CRRES MEA data to investigate the general variations in electron PAD at particular energies, in this study we present a detailed statistical analysis of electron PADs including the dependence on electron kinetic energy, magnetic local time (MLT), and the level of geomagnetic activity. By fitting the measured PADs with a power law function of sine of local Pitch Angle, the power law index n that relates to the category of radiation belt electron PAD is quantified in detail as a function of electron kinetic energy, MLT interval, and geomagnetic index Kp. Statistical averaged n values vary considerably with respect to MLT, ranging from n ∼ 0 within 0000–0400 MLT to n ∼ 1.5 within 1200–1600 MLT, because of the MLT dependence of wave scattering and the effects associated with drift shell splitting and magnetopause shadowing. Drift shell splitting and magnetopause shadowing result in often observed negative values of n. At lower energies of a few hundred keV the Pitch Angle distributions are more flat than at MeV energies, which is consistent with faster Pitch Angle scattering at low energies by chorus waves. These quantitative results of radiation belt electron PAD, consistent with the previous studies by Vampola (1998) and Gannon et al. (2007), provide further insight into the global dynamics of energetic radiation belt electrons near the geostationary orbit and also are useful for inferring electron phase space densities and assimilating their radial profiles using omnidirectional electron flux measurements.
Song Fu - One of the best experts on this subject based on the ideXlab platform.
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hot plasma effects on the cyclotron resonant Pitch Angle scattering rates of radiation belt electrons due to emic waves
Geophysical Research Letters, 2018Co-Authors: Binbin Ni, Yuri Shprits, Xudong Gu, Danny Summers, Song FuAbstract:To investigate the hot plasma effects on the cyclotron-resonant interactions between electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons in a realistic magnetospheric environment, calculations of the wave-induced bounce-averaged Pitch Angle diffusion coefficients are performed using both the cold and hot plasma dispersion relations. The results demonstrate that the hot plasma effects have a pronounced influence on the electron Pitch Angle scattering rates due to all three EMIC emission bands (H+, He+, and O+) when the hot plasma dispersion relation deviates significantly from the cold plasma approximation. For a given wave spectrum, the modification of the dispersion relation by hot anisotropic protons can strongly increase the minimum resonant energy for electrons interacting with O+ band EMIC waves, while the minimum resonant energies for H+ and He+ bands are not greatly affected. For H+ band EMIC waves, inclusion of hot protons tends to weaken the Pitch Angle scattering efficiency of >5 MeV electrons. The most crucial differences introduced by the hot plasma effects occur for >3 MeV electron scattering rates by He+ band EMIC waves. Mainly due to the changes of resonant frequency and wave group velocity when the hot protons are included, the difference in scattering rates can be up to an order of magnitude, showing a strong dependence on both electron energy and equatorial Pitch Angle. Our study confirms the importance of including hot plasma effects in modeling the scattering of ultra-relativistic radiation belt electrons by EMIC waves.
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hot plasma effects on the cyclotron resonant Pitch Angle scattering rates of radiation belt electrons due to emic waves
Geophysical Research Letters, 2018Co-Authors: Binbin Ni, Yuri Shprits, Xudong Gu, Danny Summers, Song FuAbstract:To investigate the hot plasma effects on the cyclotron-resonant interactions between electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons in a realistic magnetospheric environment, calculations of the wave-induced bounce-averaged Pitch Angle diffusion coefficients are performed using both the cold and hot plasma dispersion relations. The results demonstrate that the hot plasma effects have a pronounced influence on the electron Pitch Angle scattering rates due to all three EMIC emission bands (H+, He+, and O+) when the hot plasma dispersion relation deviates significantly from the cold plasma approximation. For a given wave spectrum, the modification of the dispersion relation by hot anisotropic protons can strongly increase the minimum resonant energy for electrons interacting with O+ band EMIC waves, while the minimum resonant energies for H+ and He+ bands are not greatly affected. For H+ band EMIC waves, inclusion of hot protons tends to weaken the Pitch Angle scattering efficiency of >5 MeV electrons. The most crucial differences introduced by the hot plasma effects occur for >3 MeV electron scattering rates by He+ band EMIC waves. Mainly due to the changes of resonant frequency and wave group velocity when the hot protons are included, the difference in scattering rates can be up to an order of magnitude, showing a strong dependence on both electron energy and equatorial Pitch Angle. Our study confirms the importance of including hot plasma effects in modeling the scattering of ultra-relativistic radiation belt electrons by EMIC waves.
Danny Summers - One of the best experts on this subject based on the ideXlab platform.
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hot plasma effects on the cyclotron resonant Pitch Angle scattering rates of radiation belt electrons due to emic waves
Geophysical Research Letters, 2018Co-Authors: Binbin Ni, Yuri Shprits, Xudong Gu, Danny Summers, Song FuAbstract:To investigate the hot plasma effects on the cyclotron-resonant interactions between electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons in a realistic magnetospheric environment, calculations of the wave-induced bounce-averaged Pitch Angle diffusion coefficients are performed using both the cold and hot plasma dispersion relations. The results demonstrate that the hot plasma effects have a pronounced influence on the electron Pitch Angle scattering rates due to all three EMIC emission bands (H+, He+, and O+) when the hot plasma dispersion relation deviates significantly from the cold plasma approximation. For a given wave spectrum, the modification of the dispersion relation by hot anisotropic protons can strongly increase the minimum resonant energy for electrons interacting with O+ band EMIC waves, while the minimum resonant energies for H+ and He+ bands are not greatly affected. For H+ band EMIC waves, inclusion of hot protons tends to weaken the Pitch Angle scattering efficiency of >5 MeV electrons. The most crucial differences introduced by the hot plasma effects occur for >3 MeV electron scattering rates by He+ band EMIC waves. Mainly due to the changes of resonant frequency and wave group velocity when the hot protons are included, the difference in scattering rates can be up to an order of magnitude, showing a strong dependence on both electron energy and equatorial Pitch Angle. Our study confirms the importance of including hot plasma effects in modeling the scattering of ultra-relativistic radiation belt electrons by EMIC waves.
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hot plasma effects on the cyclotron resonant Pitch Angle scattering rates of radiation belt electrons due to emic waves
Geophysical Research Letters, 2018Co-Authors: Binbin Ni, Yuri Shprits, Xudong Gu, Danny Summers, Song FuAbstract:To investigate the hot plasma effects on the cyclotron-resonant interactions between electromagnetic ion cyclotron (EMIC) waves and radiation belt electrons in a realistic magnetospheric environment, calculations of the wave-induced bounce-averaged Pitch Angle diffusion coefficients are performed using both the cold and hot plasma dispersion relations. The results demonstrate that the hot plasma effects have a pronounced influence on the electron Pitch Angle scattering rates due to all three EMIC emission bands (H+, He+, and O+) when the hot plasma dispersion relation deviates significantly from the cold plasma approximation. For a given wave spectrum, the modification of the dispersion relation by hot anisotropic protons can strongly increase the minimum resonant energy for electrons interacting with O+ band EMIC waves, while the minimum resonant energies for H+ and He+ bands are not greatly affected. For H+ band EMIC waves, inclusion of hot protons tends to weaken the Pitch Angle scattering efficiency of >5 MeV electrons. The most crucial differences introduced by the hot plasma effects occur for >3 MeV electron scattering rates by He+ band EMIC waves. Mainly due to the changes of resonant frequency and wave group velocity when the hot protons are included, the difference in scattering rates can be up to an order of magnitude, showing a strong dependence on both electron energy and equatorial Pitch Angle. Our study confirms the importance of including hot plasma effects in modeling the scattering of ultra-relativistic radiation belt electrons by EMIC waves.
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Pitch Angle scattering rates in planetary magnetospheres
Journal of Plasma Physics, 2005Co-Authors: Danny Summers, R. L. Mace, Manfred A HellbergAbstract:The mechanism of gyroresonant scattering of charged particles by small-amplitude, broadband electromagnetic waves is examined. By means of quasi-linear theory, a simple expression for the resonant Pitch-Angle diffusion coefficient $D_{\alpha \alpha}$ is developed, which is valid for parallel-propagating, small-amplitude, (R-mode or L-mode) electromagnetic waves of general spectral density. We calculate the average diffusion coefficient with respect to the Pitch-Angle $\alpha$ , namely $\lAngle D_{\alpha\alpha}\rAngle$ , which provides a practical estimate for particle scattering rates as a function of particle kinetic energy. The results for $\lAngle D_{\alpha\alpha}\rAngle$ , corresponding to a Gaussian wave frequency spectrum, are used to estimate scattering rates for several types of wave–particle interactions in the terrestrial and Jovian magnetospheres.
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relativistic electron Pitch Angle scattering by electromagnetic ion cyclotron waves during geomagnetic storms
Journal of Geophysical Research, 2003Co-Authors: Danny Summers, R M ThorneAbstract:During magnetic storms, relativistic electrons execute nearly circular orbits about the Earth and traverse a spatially confined zone within the duskside plasmapause where electromagnetic ion cyclotron (EMIC) waves are preferentially excited. We examine the mechanism of electron Pitch-Angle diffusion by gyroresonant interaction with EMIC waves as a cause of relativistic electron precipitation loss from the outer radiation belt. Detailed calculations are carried out of electron cyclotron resonant Pitch-Angle diffusion coefficients Dααfor EMIC waves in a multi-ion (H+, He+, O+) plasma. A simple functional form for Dαα is used, based on quasi-linear theory that is valid for parallel-propagating, small-amplitude electromagnetic waves of general spectral density. For typical observed EMIC wave amplitudes (l-10nT), the rates of resonant Pitch-Angle diffusion are close to the limit of "strong" diffusion, leading to intense electron precipitation. In order for gyroresonance to take place, electrons must possess a minimum kinetic energy Emin which depends on the value of the ratio (electron plasma frequency/ electron gyrofrequency); Emin also depends on the properties of the EMIC wave spectrum and the ion composition. Geophysically interesting scattering, with Emin comparable to 1 MeV, can only occur in regions where (electron plasma frequency/electron gyrofrequency) ≥ 10, which typically occurs within the duskside plasmapause. Under such conditions, electrons with energy ≥ 1 MeV can be removed from the outer radiation belt by EMIC wave scattering during a magnetic storm over a time-scale of several hours to a day.
