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D N Baker - One of the best experts on this subject based on the ideXlab platform.

  • rapid outer radiation belt flux dropouts and fast acceleration during the march 2015 and 2013 storms the role of ultra low frequency wave transport from a dynamic outer boundary
    Journal of Geophysical Research, 2020
    Co-Authors: L G Ozeke, H E Spence, K R Murphy, S G Claudepierre, L Olifer, K Y Dufresne, S K Morley, Ian R. Mann, D N Baker
    Abstract:

    We present simulations of the outer radiation belt electron flux during the March 2015 and March 2013 storms using a Radial Diffusion model. Despite differences in Dst intensity between the two sto...

  • fast Diffusion of ultrarelativistic electrons in the outer radiation belt 17 march 2015 storm event
    Geophysical Research Letters, 2018
    Co-Authors: A N Jaynes, S R Elkington, D N Baker, X Li, M G Henderson, S G Kanekal, D Malaspina, C A Kletzing, J R Wygant
    Abstract:

    : Inward Radial Diffusion driven by ULF waves has long been known to be capable of accelerating radiation belt electrons to very high energies within the heart of the belts, but more recent work has shown that Radial Diffusion values can be highly event-specific, and mean values or empirical models may not capture the full significance of Radial Diffusion to acceleration events. Here we present an event of fast inward Radial Diffusion, occurring during a period following the geomagnetic storm of 17 March 2015. Ultrarelativistic electrons up to ∼8 MeV are accelerated in the absence of intense higher-frequency plasma waves, indicating an acceleration event in the core of the outer belt driven primarily or entirely by ULF wave-driven Diffusion. We examine this fast Diffusion rate along with derived Radial Diffusion coefficients using particle and fields instruments on the Van Allen Probes spacecraft mission.

  • ultra relativistic radiation belt extinction and ulf wave Radial Diffusion modeling the september 2014 extended dropout event
    Geophysical Research Letters, 2017
    Co-Authors: L G Ozeke, K R Murphy, I. R. Mann, D G Sibeck, D N Baker
    Abstract:

    In September 2014 an unusually long lasting (≳10 days) ultra-relativistic electron flux depletion occurred in the outer radiation belt despite ongoing solar wind forcing. We simulate this period using a ULF wave Radial Diffusion model, driven by observed ULF wave power coupled to flux variations at the outer boundary at L* = 5, including empirical electron loss models due to chorus and hiss wave scattering. Our results show that unexplained rapid main phase loss, that depletes the belt within hours, is essential to explain the observations. Such ultra-relativistic electron extinction decouples the pre- and post-storm flux, revealing the subsequent belt dynamics to be surprisingly independent of pre-storm flux. However, once this extinction is included ULF wave transport and coupling to the outer boundary explain the extended depletion event, and also the eventual flux recovery. Neither local acceleration nor ongoing losses from hiss or chorus wave scattering to the atmosphere are required.

  • radiation belt electron acceleration during the 17 march 2015 geomagnetic storm observations and simulations
    Journal of Geophysical Research, 2016
    Co-Authors: R M Thorne, Jacob Bortnik, D N Baker, Harlan E. Spence, Geoffrey D. Reeves, Craig Kletzing, George B. Hospodarsky, W S Kurth, Xiaojia Zhang, J. B. Blake
    Abstract:

    Various physical processes are known to cause acceleration, loss, and transport of energetic electrons in the Earth's radiation belts, but their quantitative roles in different time and space need further investigation. During the largest storm over the past decade (17 March 2015), relativistic electrons experienced fairly rapid acceleration up to ~7 MeV within 2 days after an initial substantial dropout, as observed by Van Allen Probes. In the present paper, we evaluate the relative roles of various physical processes during the recovery phase of this large storm using a 3-D Diffusion simulation. By quantitatively comparing the observed and simulated electron evolution, we found that chorus plays a critical role in accelerating electrons up to several MeV near the developing peak location and produces characteristic flat-top pitch angle distributions. By only including Radial Diffusion, the simulation underestimates the observed electron acceleration, while Radial Diffusion plays an important role in redistributing electrons and potentially accelerates them to even higher energies. Moreover, plasmaspheric hiss is found to provide efficient pitch angle scattering losses for hundreds of keV electrons, while its scattering effect on > 1 MeV electrons is relatively slow. Although an additional loss process is required to fully explain the overestimated electron fluxes at multi-MeV, the combined physical processes of Radial Diffusion and pitch angle and energy Diffusion by chorus and hiss reproduce the observed electron dynamics remarkably well, suggesting that quasi-linear Diffusion theory is reasonable to evaluate radiation belt electron dynamics during this big storm.

  • simulation of energy dependent electron Diffusion processes in the earth s outer radiation belt
    Journal of Geophysical Research, 2016
    Co-Authors: R M Thorne, H E Spence, G D Reeves, George B. Hospodarsky, M G Henderson, W S Kurth, Xiaojia Zhang, C A Kletzing, Y Nishimura, D N Baker
    Abstract:

    The Radial and local Diffusion processes induced by various plasma waves govern the highly energetic electron dynamics in the Earth's radiation belts, causing distinct characteristics in electron distributions at various energies. In this study, we present our simulation results of the energetic electron evolution during a geomagnetic storm using the University of California, Los Angeles 3-D Diffusion code. Following the plasma sheet electron injections, the electrons at different energy bands detected by the Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron Proton Telescope (REPT) instruments on board the Van Allen Probes exhibit a rapid enhancement followed by a slow diffusive movement in differential energy fluxes, and the Radial extent to which electrons can penetrate into depends on energy with closer penetration toward the Earth at lower energies than higher energies. We incorporate Radial Diffusion, local acceleration, and loss processes due to whistler mode wave observations to perform a 3-D Diffusion simulation. Our simulation results demonstrate that chorus waves cause electron flux increase by more than 1 order of magnitude during the first 18 h, and the subsequent Radial extents of the energetic electrons during the storm recovery phase are determined by the coupled Radial Diffusion and the pitch angle scattering by EMIC waves and plasmaspheric hiss. The Radial Diffusion caused by ULF waves and local plasma wave scattering are energy dependent, which lead to the observed electron flux variations with energy dependences. This study suggests that plasma wave distributions in the inner magnetosphere are crucial for the energy-dependent intrusions of several hundred keV to several MeV electrons.

Yuri Shprits - One of the best experts on this subject based on the ideXlab platform.

  • Dependence of radiation belt simulations to assumed Radial Diffusion rates tested for two empirical models of Radial transport
    Social Work, 2017
    Co-Authors: Alexander Drozdov, Yuri Shprits, Nikita Aseev, Adam Kellerman, Geoffrey D. Reeves
    Abstract:

    Radial Diffusion is one of the dominant physical mechanisms that drives acceleration and loss of the radiation belt electrons, which makes it very important for nowcasting and forecasting space weather models. We investigate the sensitivity of the two parameterizations of the Radial Diffusion of Brautigam and Albert [2000] and Ozeke et al. [2014] on long-term radiation belt modeling using the Versatile Electron Radiation Belt (VERB). Following Brautigam and Albert [2000] and Ozeke et al. [2014], we first perform 1-D Radial Diffusion simulations. Comparison of the simulation results with observations shows that the difference between simulations with either Radial Diffusion parameterization is small. To take into account effects of local acceleration and loss, we perform 3-D simulations, including pitch-angle, energy and mixed Diffusion. We found that the results of 3-D simulations are even less sensitive to the choice of parameterization of Radial Diffusion rates than the results of 1-D simulations at various energies (from 0.59 to 1.80 MeV). This result demonstrates that the inclusion of local acceleration and pitch-angle Diffusion can provide a negative feedback effect, such that the result is largely indistinguishable simulations conducted with different Radial Diffusion parameterizations. We also perform a number of sensitivity tests by multiplying Radial Diffusion rates by constant factors and show that such an approach leads to unrealistic predictions of radiation belt dynamics.

  • the origin of jupiter s outer radiation belt
    URSI General Assembly and Scientific Symposium, 2014
    Co-Authors: E E Woodfield, Sarah A. Glauert, Richard B Horne, J. D. Menietti, Yuri Shprits
    Abstract:

    The intense inner radiation belt at Jupiter (>50 MeV at 1.5 R J [1]) is generally accepted to be created by Radial Diffusion of electrons from further away from the planet [2]. However, this requires a source with energies that exceed 1 MeV outside the orbit of the moon Io at 5.9 R J , which has never been explained satisfactorily. Here we test the hypothesis that this source population could be formed from a very soft energy spectrum, by particle injection processes and resonant electron acceleration via whistler mode chorus waves. Using the first simulations at Jupiter combining wave particle interactions and Radial Diffusion, we calculate the change in the electron flux between 6.5 and 15 R J with the BAS Radiation Belt Model starting from a very soft spectrum. The electron flux after 30 days at 100 keV and 1 MeV lies very close to the Galileo Interim Radiation Electron (GIRE) model spectrum [3] after 1 and 10 days respectively. The primary driver for the increase in the flux is cyclotron resonant acceleration by chorus waves, which causes an increase in the flux by a factor of 106 from the soft spectrum. The Radial Diffusion does not affect the magnitude of this increase to any great extent, but acts to smooth out variations in the phase space density with L. The variation of chorus wave power with Radial distance from Jupiter results in a peak in phase space density such that inside L≈9 Radial Diffusion transports electrons towards Jupiter, but outside L≈9 Radial Diffusion acts away from the planet. The results are insensitive to the softness of the initial energy spectrum but do depend on the value of the flux at the minimum energy boundary. The overall shape of the flux after 30 days remains very similar but the magnitude of the flux at all energies is dependent on the flux at the minimum energy boundary. We show that individual injections of particles at a few tens of keV would have a cumulative effect on the increases in flux at energies of a few MeV by varying the flux at the minimum energy boundary in a time dependent manner based on the injections reported in [4]. We conclude by suggesting that the source population for the inner radiation belt at Jupiter could indeed by formed by wave-particle interactions.

  • long term relativistic radiation belt electron responses to gem magnetic storms
    Journal of Atmospheric and Solar-Terrestrial Physics, 2013
    Co-Authors: Kyungchan Kim, Yuri Shprits
    Abstract:

    Abstract We present a long-term radiation belt simulation for a 200-day period starting on 25 January 1991, which includes both six geomagnetic storms identified by the Geospace Environment Modeling (GEM) focus group and non-stormy periods of the Combined Release and Radiation Effects Satellite (CRRES) mission, using 3-D time-dependent Versatile Electron Radiation Belt (VERB) code, and compare the simulation results with a multisatellite phase space density (PSD) reanalysis obtained using Kalman filtering of observations from CRRES, GEO, GPS, and Akebono satellites, as well as with the CRRES MEA 1 MeV electron observation. The processes accounted for in the model are Radial Diffusion-driven by ultra-low frequency (ULF) electromagnetic fluctuations and local (pitch-angle and energy) scattering by plasmaspheric hiss and chorus waves, respectively, inside and outside the plasmasphere. The observations show that a significant decrease in the relativistic electrons in the outer radiation belt is observed in association with the solar wind dynamic pressure enhancement during the main phase of each storm, while during the recovery phase, different types of relativistic electron flux profiles are identified: increased, decreased, and unchanged relative to the pre-storm flux level. First, for an increase of relativistic electrons relative to the pre-storm flux level, the comparison of simulation with reanalysis shows that inward Radial Diffusion and local acceleration coupled with each other result in a net acceleration. Second, for a decrease or lack of change in relativistic electrons, competing effects of pitch-angle scattering, outward Diffusion, and acceleration produce the net decrease in electron PSD and fluxes. The results show that the overall time evolution of the radiation belt is in good agreement with our model simulations, indicating that modeling, including Radial Diffusion and pitch-angle scattering, is reasonable in predicting the general long-term structure of the outer radiation belt. In addition, with the assistance of local acceleration by chorus waves, the overall flux level in the outer radiation belt becomes comparable to the observation.

  • understanding the dynamic evolution of the relativistic electron slot region including Radial and pitch angle Diffusion
    Journal of Geophysical Research, 2011
    Co-Authors: Yuri Shprits, D Subbotin, Binbin Ni
    Abstract:

    [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.

  • electron flux changes in the outer radiation belt by Radial Diffusion during the storm recovery phase in comparison with the fully adiabatic evolution
    Journal of Geophysical Research, 2011
    Co-Authors: Yuri Shprits
    Abstract:

    [1] The Radial Diffusion process can play an important role in redistributing the radiation belt electron fluxes. In this work, we have performed 1-D Radial Diffusion simulations to examine the evolution of the phase space density (PSD) of the outer radiation belt electrons and to estimate the corresponding fluxes during the storm recovery phase. The key element that distinguishes our simulations from previous works is the initial condition for PSD, which is characterized by a steep Radial gradient across the trapping boundary. In our simulations, this condition is formed as a result of the drift loss effect of particles during the storm main phase, and the simulations of Radial Diffusion were run for the storm recovery phase. We performed the study for three classes of geomagnetic storms of different intensities, i.e., the moderate (−100 nT < Dstmin ≤ −50 nT), strong (−150 nT < Dstmin ≤ −100 nT), and severe (Dstmin ≤ −150 nT) storms. The effects of Radial Diffusion in PSD are notable in the following respects. First, the Radial Diffusion process is very significant for the initial few hours of the storm recovery phase. Second, the effect of the Radial Diffusion occurs in both inward and outward directions, thus affecting a wide range of L regions. The inward Diffusion causes the PSD peak to move inward. The regions outside of the initial trapping boundary are refilled with finite PSD by the outward Radial Diffusion. Consequently, the combination of these effects results in different levels and patterns in the directional and omni-directional fluxes from those expected from a fully adiabatic evolution throughout the entire storm period. Last, the details of the PSD evolution, and thus its effect on the corresponding flux levels and patterns, differ among storms of different intensities. We report these differences in detail.

S R Elkington - One of the best experts on this subject based on the ideXlab platform.

  • fast Diffusion of ultrarelativistic electrons in the outer radiation belt 17 march 2015 storm event
    Geophysical Research Letters, 2018
    Co-Authors: A N Jaynes, S R Elkington, D N Baker, X Li, M G Henderson, S G Kanekal, D Malaspina, C A Kletzing, J R Wygant
    Abstract:

    : Inward Radial Diffusion driven by ULF waves has long been known to be capable of accelerating radiation belt electrons to very high energies within the heart of the belts, but more recent work has shown that Radial Diffusion values can be highly event-specific, and mean values or empirical models may not capture the full significance of Radial Diffusion to acceleration events. Here we present an event of fast inward Radial Diffusion, occurring during a period following the geomagnetic storm of 17 March 2015. Ultrarelativistic electrons up to ∼8 MeV are accelerated in the absence of intense higher-frequency plasma waves, indicating an acceleration event in the core of the outer belt driven primarily or entirely by ULF wave-driven Diffusion. We examine this fast Diffusion rate along with derived Radial Diffusion coefficients using particle and fields instruments on the Van Allen Probes spacecraft mission.

  • electric and magnetic Radial Diffusion coefficients using the van allen probes data
    Journal of Geophysical Research, 2016
    Co-Authors: A Ali, S R Elkington, Anthony A Chan, D Malaspina, A N Jaynes, J R Wygant, C A Kletzing
    Abstract:

    ULF waves are a common occurrence in the inner magnetosphere and they contribute to particle motion, significantly, at times. We used the magnetic and the electric field data from the Electric and Magnetic Field Instrument Suite and Integrated Sciences (EMFISIS) and the Electric Field and Waves instruments (EFW) on board the Van Allen Probes to estimate the ULF wave power in the compressional component of the magnetic field and the azimuthal component of the electric field, respectively. Using L∗, Kp, and magnetic local time (MLT) as parameters, we conclude that the noon sector contains higher ULF Pc-5 wave power compared with the other MLT sectors. The dawn, dusk, and midnight sectors have no statistically significant difference between them. The drift-averaged power spectral densities are used to derive the magnetic and the electric component of the Radial Diffusion coefficient. Both components exhibit little to no energy dependence, resulting in simple analytic models for both components. More importantly, the electric component is larger than the magnetic component by one to two orders of magnitude for almost all L∗ and Kp; thus, the electric field perturbations are more effective in driving Radial Diffusion of charged particles in the inner magnetosphere. We also present a comparison of the Van Allen Probes Radial Diffusion coefficients, including the error estimates, with some of the previous published results. This allows us to gauge the large amount of uncertainty present in such estimates.

  • magnetic field power spectra and magnetic Radial Diffusion coefficients using crres magnetometer data
    Journal of Geophysical Research, 2015
    Co-Authors: A Ali, S R Elkington, L G Ozeke, Anthony A Chan, R. H. W. Friedel
    Abstract:

    We used the fluxgate magnetometer data from Combined Release and Radiation Effects Satellite (CRRES) to estimate the power spectral density (PSD) of the compressional component of the geomagnetic field in the ∼1 mHz to ∼8 mHz range. We conclude that magnetic wave power is generally higher in the noon sector for quiet times with no significant difference between the dawn, dusk, and the midnight sectors. However, during high Kp activity, the noon sector is not necessarily dominant anymore. The magnetic PSDs have a very distinct dependence on Kp. In addition, the PSDs appear to have a weak dependence on McIlwain parameter L with power slightly increasing as L increases. The magnetic wave PSDs are used along with the Fei et al. (2006) formulation to compute DLLB[CRRES] as a function of L and Kp. The L dependence of DLLB[CRRES] is systematically studied and is shown to depend on Kp. More significantly, we conclude that DLLEis the dominant term driving Radial Diffusion, typically exceeding DLLB by 1–2 orders of magnitude.

  • three dimensional stochastic modeling of radiation belts in adiabatic invariant coordinates
    Journal of Geophysical Research, 2014
    Co-Authors: Liheng Zheng, J M Albert, S R Elkington, Richard B Horne, Sarah A. Glauert, J Koller, Anthony A Chan, Nigel P. Meredith
    Abstract:

    A 3-D model for solving the radiation belt Diffusion equation in adiabatic invariant coordinates has been developed and tested. The model, named REM (for Radbelt Electron Model), obtains a probabilistic solution by solving a set of Ito stochastic differential equations that are mathematically equivalent to the Diffusion equation. This method is capable of solving Diffusion equations with a full 3-D Diffusion tensor, including the Radial-local cross Diffusion components. The correct form of the boundary condition at equatorial pitch-angle α0 = 90° is also derived. The model is applied to a simulation of the October 2002 storm event. At α0 near 90°, our results are quantitatively consistent with GPS observations of phase-space density (PSD) increases, suggesting dominance of Radial Diffusion; at smaller α0, the observed PSD increases are overestimated by the model, possibly due to the α0-independent Radial Diffusion coefficients, or to insufficientelectron loss in the model, or both. Statistical analysis of the stochastic processes provides further insights into the Diffusion processes, showing distinctive electron source distributions with and without local acceleration.

  • quantifying Radial Diffusion coefficients of radiation belt electrons based on global mhd simulation and spacecraft measurements
    Journal of Geophysical Research, 2012
    Co-Authors: S R Elkington, Wenlong Liu, J W Bonnell
    Abstract:

    [1] Radial Diffusion is one of the most important acceleration mechanisms for radiation belt electrons, which can be enhanced from drift-resonant interactions with large-scale fluctuations of the magnetosphere's magnetic and electric fields (Pc5 range of ULF waves). In order to physically quantify the Radial Diffusion coefficient,DLL, we run the global Lyon-Fedder-Mobarry (LFM) MHD simulations to obtain the mode structure and power spectrum of the ULF waves and validate the simulation results with available satellite measurements. The calculated Diffusion coefficients, directly from the MHD fields over a Corotating Interaction Region (CIR) storm in March 2008, are generally higher when solar wind dynamic pressure is enhanced or AE index is high. In contrary to the conventional understanding, our results show that inside geosynchronous orbit the total Diffusion coefficient from MHD fields is dominated by the contribution from electric field perturbations, rather than the magnetic field perturbations. The calculated Diffusion coefficient has a physical dependence onμ (or electron energy) and L, which is missing in the empirical Diffusion coefficient, DLLKp as a function of Kp index, and DLLKp are generally greater than our calculated DLLduring the storm event. Validation of the MHD ULF waves by spacecraft field data shows that for this event the LFM code reasonably well-reproduces theBz wave power observed by GOES and THEMIS satellites, while the Eφ power observed by THEMIS probes are generally underestimated by LFM fields, on average by about a factor of ten.

R M Thorne - One of the best experts on this subject based on the ideXlab platform.

  • diffusive transport of several hundred kev electrons in the earth s slot region
    Journal of Geophysical Research, 2017
    Co-Authors: R M Thorne, H E Spence, S G Claudepierre, Jacob Bortnik, G D Reeves, Craig Kletzing, J. B. Blake, J F Fennell, D L Turner, W S Kurth
    Abstract:

    We investigate the gradual Diffusion of energetic electrons from the inner edge of the outer radiation belt into the slot region. The Van Allen Probes observed slow inward Diffusion and decay of ~200–600 keV electrons following the intense geomagnetic storm that occurred on 17 March 2013. During the 10 day nondisturbed period following the storm, the peak of electron fluxes gradually moved from L ~ 2.7 to L ~ 2.4, and the flux levels decreased by a factor of ~2–4 depending on the electron energy. We simulated the Radial intrusion and decay of electrons using a three-dimensional Diffusion code, which reproduced the energy-dependent transport of electrons from ~100 keV to 1 MeV in the slot region. At energies of 100–200 keV, the electrons experience fast transport across the slot region due to the dominance of Radial Diffusion; at energies of 200–600 keV, the electrons gradually diffuse and decay in the slot region due to the comparable rate of Radial Diffusion and pitch angle scattering by plasmaspheric hiss; at energies of E > 700 keV, the electrons stopped diffusing near the inner edge of outer radiation belt due to the dominant pitch angle scattering loss. In addition to plasmaspheric hiss, magnetosonic waves and VLF transmitters can cause the loss of high pitch angle electrons, relaxing the sharp “top-hat” shaped pitch angle distributions created by plasmaspheric hiss. Our simulation indicates the importance of balance between Radial Diffusion and loss through pitch angle scattering in forming the diffusive intrusion of energetic electrons across the slot region.

  • radiation belt electron acceleration during the 17 march 2015 geomagnetic storm observations and simulations
    Journal of Geophysical Research, 2016
    Co-Authors: R M Thorne, Jacob Bortnik, D N Baker, Harlan E. Spence, Geoffrey D. Reeves, Craig Kletzing, George B. Hospodarsky, W S Kurth, Xiaojia Zhang, J. B. Blake
    Abstract:

    Various physical processes are known to cause acceleration, loss, and transport of energetic electrons in the Earth's radiation belts, but their quantitative roles in different time and space need further investigation. During the largest storm over the past decade (17 March 2015), relativistic electrons experienced fairly rapid acceleration up to ~7 MeV within 2 days after an initial substantial dropout, as observed by Van Allen Probes. In the present paper, we evaluate the relative roles of various physical processes during the recovery phase of this large storm using a 3-D Diffusion simulation. By quantitatively comparing the observed and simulated electron evolution, we found that chorus plays a critical role in accelerating electrons up to several MeV near the developing peak location and produces characteristic flat-top pitch angle distributions. By only including Radial Diffusion, the simulation underestimates the observed electron acceleration, while Radial Diffusion plays an important role in redistributing electrons and potentially accelerates them to even higher energies. Moreover, plasmaspheric hiss is found to provide efficient pitch angle scattering losses for hundreds of keV electrons, while its scattering effect on > 1 MeV electrons is relatively slow. Although an additional loss process is required to fully explain the overestimated electron fluxes at multi-MeV, the combined physical processes of Radial Diffusion and pitch angle and energy Diffusion by chorus and hiss reproduce the observed electron dynamics remarkably well, suggesting that quasi-linear Diffusion theory is reasonable to evaluate radiation belt electron dynamics during this big storm.

  • simulation of energy dependent electron Diffusion processes in the earth s outer radiation belt
    Journal of Geophysical Research, 2016
    Co-Authors: R M Thorne, H E Spence, G D Reeves, George B. Hospodarsky, M G Henderson, W S Kurth, Xiaojia Zhang, C A Kletzing, Y Nishimura, D N Baker
    Abstract:

    The Radial and local Diffusion processes induced by various plasma waves govern the highly energetic electron dynamics in the Earth's radiation belts, causing distinct characteristics in electron distributions at various energies. In this study, we present our simulation results of the energetic electron evolution during a geomagnetic storm using the University of California, Los Angeles 3-D Diffusion code. Following the plasma sheet electron injections, the electrons at different energy bands detected by the Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron Proton Telescope (REPT) instruments on board the Van Allen Probes exhibit a rapid enhancement followed by a slow diffusive movement in differential energy fluxes, and the Radial extent to which electrons can penetrate into depends on energy with closer penetration toward the Earth at lower energies than higher energies. We incorporate Radial Diffusion, local acceleration, and loss processes due to whistler mode wave observations to perform a 3-D Diffusion simulation. Our simulation results demonstrate that chorus waves cause electron flux increase by more than 1 order of magnitude during the first 18 h, and the subsequent Radial extents of the energetic electrons during the storm recovery phase are determined by the coupled Radial Diffusion and the pitch angle scattering by EMIC waves and plasmaspheric hiss. The Radial Diffusion caused by ULF waves and local plasma wave scattering are energy dependent, which lead to the observed electron flux variations with energy dependences. This study suggests that plasma wave distributions in the inner magnetosphere are crucial for the energy-dependent intrusions of several hundred keV to several MeV electrons.

  • modeling inward Diffusion and slow decay of energetic electrons in the earth s outer radiation belt
    Geophysical Research Letters, 2015
    Co-Authors: R M Thorne, H E Spence, G D Reeves, D N Baker, Craig Kletzing, George B. Hospodarsky, J. B. Blake, M G Henderson, W S Kurth, J F Fennell
    Abstract:

    ©2015. American Geophysical Union. All Rights Reserved. A new 3-D Diffusion code is used to investigate the inward intrusion and slow decay of energetic radiation belt electrons (>0.5MeV) observed by the Van Allen Probes during a 10day 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.

  • reanalysis of relativistic radiation belt electron fluxes using crres satellite data a Radial Diffusion model and a kalman filter
    Journal of Geophysical Research, 2007
    Co-Authors: Dmitri Kondrashov, R. H. W. Friedel, Yue Che, R M Thorne, Michael Ghil, G D Reeves
    Abstract:

    [1] In this study we perform a reanalysis of the sparse MEA CRRES relativistic electron data using a relatively simple one-dimensional Radial Diffusion model and a Kalman filtering approach. By combining observations with the model in an optimal way we produce a high time and space resolution reanalysis of the radiation belt electron fluxes over a 50-d period starting on 18 August 1990. The results of the reanalysis clearly show pronounced peaks in the electron phase space density (PSD), which can not be explained by the variations in the outer boundary, and can only be produced by a local acceleration processes. The location of the innovation vector shows that local acceleration is most efficient at L* = 5.5 for electrons at K = 0.11 G0.5REand μ = 700 MeV/G. Sensitivity numerical experiments for various values of μ and K indicate that peaks in PSD become stronger with increasing K and μ. To verify that our results are not affected by the limitations of the satellite orbit and coverage, we performed an “identical twin” experiments with synthetic data specified only at the locations for which CRRES observations are available. Our results indicate that the model with data assimilation can accurately reproduce the underlying structure of the PSD even when data is sparse. The identical twin experiments also indicate that PSD at a particular L-shell is determined by the local processes and cannot be accurately estimated unless local measurements are available.

G D Reeves - One of the best experts on this subject based on the ideXlab platform.

  • diffusive transport of several hundred kev electrons in the earth s slot region
    Journal of Geophysical Research, 2017
    Co-Authors: R M Thorne, H E Spence, S G Claudepierre, Jacob Bortnik, G D Reeves, Craig Kletzing, J. B. Blake, J F Fennell, D L Turner, W S Kurth
    Abstract:

    We investigate the gradual Diffusion of energetic electrons from the inner edge of the outer radiation belt into the slot region. The Van Allen Probes observed slow inward Diffusion and decay of ~200–600 keV electrons following the intense geomagnetic storm that occurred on 17 March 2013. During the 10 day nondisturbed period following the storm, the peak of electron fluxes gradually moved from L ~ 2.7 to L ~ 2.4, and the flux levels decreased by a factor of ~2–4 depending on the electron energy. We simulated the Radial intrusion and decay of electrons using a three-dimensional Diffusion code, which reproduced the energy-dependent transport of electrons from ~100 keV to 1 MeV in the slot region. At energies of 100–200 keV, the electrons experience fast transport across the slot region due to the dominance of Radial Diffusion; at energies of 200–600 keV, the electrons gradually diffuse and decay in the slot region due to the comparable rate of Radial Diffusion and pitch angle scattering by plasmaspheric hiss; at energies of E > 700 keV, the electrons stopped diffusing near the inner edge of outer radiation belt due to the dominant pitch angle scattering loss. In addition to plasmaspheric hiss, magnetosonic waves and VLF transmitters can cause the loss of high pitch angle electrons, relaxing the sharp “top-hat” shaped pitch angle distributions created by plasmaspheric hiss. Our simulation indicates the importance of balance between Radial Diffusion and loss through pitch angle scattering in forming the diffusive intrusion of energetic electrons across the slot region.

  • simulation of energy dependent electron Diffusion processes in the earth s outer radiation belt
    Journal of Geophysical Research, 2016
    Co-Authors: R M Thorne, H E Spence, G D Reeves, George B. Hospodarsky, M G Henderson, W S Kurth, Xiaojia Zhang, C A Kletzing, Y Nishimura, D N Baker
    Abstract:

    The Radial and local Diffusion processes induced by various plasma waves govern the highly energetic electron dynamics in the Earth's radiation belts, causing distinct characteristics in electron distributions at various energies. In this study, we present our simulation results of the energetic electron evolution during a geomagnetic storm using the University of California, Los Angeles 3-D Diffusion code. Following the plasma sheet electron injections, the electrons at different energy bands detected by the Magnetic Electron Ion Spectrometer (MagEIS) and Relativistic Electron Proton Telescope (REPT) instruments on board the Van Allen Probes exhibit a rapid enhancement followed by a slow diffusive movement in differential energy fluxes, and the Radial extent to which electrons can penetrate into depends on energy with closer penetration toward the Earth at lower energies than higher energies. We incorporate Radial Diffusion, local acceleration, and loss processes due to whistler mode wave observations to perform a 3-D Diffusion simulation. Our simulation results demonstrate that chorus waves cause electron flux increase by more than 1 order of magnitude during the first 18 h, and the subsequent Radial extents of the energetic electrons during the storm recovery phase are determined by the coupled Radial Diffusion and the pitch angle scattering by EMIC waves and plasmaspheric hiss. The Radial Diffusion caused by ULF waves and local plasma wave scattering are energy dependent, which lead to the observed electron flux variations with energy dependences. This study suggests that plasma wave distributions in the inner magnetosphere are crucial for the energy-dependent intrusions of several hundred keV to several MeV electrons.

  • modeling inward Diffusion and slow decay of energetic electrons in the earth s outer radiation belt
    Geophysical Research Letters, 2015
    Co-Authors: R M Thorne, H E Spence, G D Reeves, D N Baker, Craig Kletzing, George B. Hospodarsky, J. B. Blake, M G Henderson, W S Kurth, J F Fennell
    Abstract:

    ©2015. American Geophysical Union. All Rights Reserved. A new 3-D Diffusion code is used to investigate the inward intrusion and slow decay of energetic radiation belt electrons (>0.5MeV) observed by the Van Allen Probes during a 10day 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.

  • event specific chorus wave and electron seed population models in dream3d using the van allen probes
    Geophysical Research Letters, 2014
    Co-Authors: Gregory S Cunningham, S K Morley, G D Reeves, D N Baker, J. B. Blake, Y Chen, H E Spence
    Abstract:

    The DREAM3D Diffusion model is applied to Van Allen Probes observations of the fast dropout and strong enhancement of MeV electrons during the October 2012 “double-dip” storm. We show that in order to explain the very different behavior in the two “dips,” Diffusion in all three dimensions (energy, pitch angle, and L*) coupled with data-driven, event-specific inputs, and boundary conditions is required. Specifically, we find that outward Radial Diffusion to the solar wind-driven magnetopause, an event-specific chorus wave model, and a dynamic lower-energy seed population are critical for modeling the dynamics. In contrast, models that include only a subset of processes, use statistical wave amplitudes, or rely on inward Radial Diffusion of a seed population, perform poorly. The results illustrate the utility of the high resolution, comprehensive set of Van Allen Probes' measurements in studying the balance between source and loss in the radiation belt, a principal goal of the mission.

  • modeling radiation belt electron dynamics during gem challenge intervals with the dream3d Diffusion model
    Journal of Geophysical Research, 2013
    Co-Authors: Gregory S Cunningham, M G Henderson, Enrico Camporeale, Y Chen, G D Reeves
    Abstract:

    As a response to the Geospace Environment Modeling (GEM) “Global Radiation Belt Modeling Challenge,” a 3D Diffusion model is used to simulate the radiation belt electron dynamics during two intervals of the Combined Release and Radiation Effects Satellite (CRRES) mission, 15 August to 15 October 1990 and 1 February to 31 July 1991. The 3D Diffusion model, developed as part of the Dynamic Radiation Environment Assimilation Model (DREAM) project, includes Radial, pitch angle, and momentum Diffusion and mixed pitch angle-momentum Diffusion, which are driven by dynamic wave databases from the statistical CRRES wave data, including plasmaspheric hiss, lower-band, and upper-band chorus. By comparing the DREAM3D model outputs to the CRRES electron phase space density (PSD) data, we find that, with a data-driven boundary condition at Lmax = 5.5, the electron enhancements can generally be explained by Radial Diffusion, though additional local heating from chorus waves is required. Because the PSD reductions are included in the boundary condition at Lmax = 5.5, our model captures the fast electron dropouts over a large L range, producing better model performance compared to previous published results. Plasmaspheric hiss produces electron losses inside the plasmasphere, but the model still sometimes overestimates the PSD there. Test simulations using reduced Radial Diffusion coefficients or increased pitch angle Diffusion coefficients inside the plasmasphere suggest that better wave models and more realistic Radial Diffusion coefficients, both inside and outside the plasmasphere, are needed to improve the model performance. Statistically, the results show that, with the data-driven outer boundary condition, including Radial Diffusion and plasmaspheric hiss is sufficient to model the electrons during geomagnetically quiet times, but to best capture the radiation belt variations during active times, pitch angle and momentum Diffusion from chorus waves are required.