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Found 8 entries in the Bibliography.
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2020 
The Effect of Plasma Boundaries on the Dynamic Evolution of Relativistic Radiation Belt Electrons Abstract Understanding the dynamic evolution of relativistic electrons in the Earth s radiation belts during both storm and nonstorm times is a challenging task. The U.S. National Science Foundation s Geospace Environment Modeling (GEM) focus group “Quantitative Assessment of Radiation Belt Modeling” has selected two storm time and two nonstorm time events that occurred during the second year of the Van Allen Probes mission for indepth study. Here, we perform simulations for these GEM challenge events using the 3D Versatile Electron Radiation Belt code. We set up the outer L* boundary using data from the Geostationary Operational Environmental Satellites and validate the simulation results against satellite observations from both the Geostationary Operational Environmental Satellites and Van Allen Probe missions for 0.9MeV electrons. Our results show that the position of the plasmapause plays a significant role in the dynamic evolution of relativistic electrons. The magnetopause shadowing effect is included by using last closed drift shell, and it is shown to significantly contribute to the dropouts of relativistic electrons at high L*. We perform simulations using four different empirical radial diffusion coefficient models for the GEM challenge events, and the results show that these simulations reproduce the general dynamic evolution of relativistic radiation belt electrons. However, in the events shown here, simulations using the radial diffusion coefficients from Brautigam and Albert (2000) produce the best agreement with satellite observations. Wang, Dedong; Shprits, Yuri; Zhelavskaya, Irina; Effenberger, Frederic; Castillo, Angelica; Drozdov, Alexander; Aseev, Nikita; Cervantes, Sebastian; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: 10.1029/2019JA027422 Radiation belt; simulation; relativistic electrons; magnetopause shadowing; Waveparticle interaction; Plasmapause; Van Allen Probes 
The Effect of Plasma Boundaries on the Dynamic Evolution of Relativistic Radiation Belt Electrons Understanding the dynamic evolution of relativistic electrons in the Earth s radiation belts during both storm and nonstorm times is a challenging task. The U.S. National Science Foundation s Geospace Environment Modeling (GEM) focus group “Quantitative Assessment of Radiation Belt Modeling” has selected two storm time and two nonstorm time events that occurred during the second year of the Van Allen Probes mission for indepth study. Here, we perform simulations for these GEM challenge events using the 3D Versatile Electron Radiation Belt code. We set up the outer L* boundary using data from the Geostationary Operational Environmental Satellites and validate the simulation results against satellite observations from both the Geostationary Operational Environmental Satellites and Van Allen Probe missions for 0.9MeV electrons. Our results show that the position of the plasmapause plays a significant role in the dynamic evolution of relativistic electrons. The magnetopause shadowing effect is included by using last closed drift shell, and it is shown to significantly contribute to the dropouts of relativistic electrons at high L*. We perform simulations using four different empirical radial diffusion coefficient models for the GEM challenge events, and the results show that these simulations reproduce the general dynamic evolution of relativistic radiation belt electrons. However, in the events shown here, simulations using the radial diffusion coefficients from Brautigam and Albert (2000) produce the best agreement with satellite observations. Wang, Dedong; Shprits, Yuri; Zhelavskaya, Irina; Effenberger, Frederic; Castillo, Angelica; Drozdov, Alexander; Aseev, Nikita; Cervantes, Sebastian; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2019JA027422 Radiation belt; simulation; relativistic electrons; magnetopause shadowing; Waveparticle interaction; Plasmapause; Van Allen Probes 
2018 
Simulations of Van Allen Probes Plasmaspheric Electron Density Observations We simulate equatorial plasmaspheric electron densities using a physicsbased model (Cold PLasma, CPL; used in the ring currentatmosphere interactions model) of the source and loss processes of refilling and erosion driven by empirical inputs. The performance of CPL is evaluated against in situ measurements by the Van Allen Probes (Radiation Belt Storm Probes) for two events: the 31 May to 5 June and 15 to 20 January 2013 geomagnetic storms observed in the premidnight and postmidnight magnetic local time (MLT) sectors, respectively. Overall, CPL reproduces the radial extent of the plasmasphere to within a mean absolute difference of urn:xwiley:jgra:media:jgra54637:jgra54637math0001 L. The model electric field responsible for E \texttimes B convection and the parameterization of geomagnetic conditions (under the Kpindex and solar wind properties) implemented by CPL did not account for localized enhancements in the duskward electric field during increased activity. Rather, it was found to be largely dependent on the measure of the quiet time background. This property indicates that the agreement between these simulations and observations does not account for the complete set of physical processes during extreme (strong or weak) geomagnetic conditions impacting the plasmasphere. Nevertheless, at the presented resolution of the model CPL does provide good agreement in reproducing Radiation Belt Storm Probes observations of plasmaspheric density and plasmapause location. De Pascuale, S.; Jordanova, V.; Goldstein, J.; Kletzing, C.; Kurth, W.; Thaller, S.; Wygant, J.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2018 YEAR: 2018 DOI: 10.1029/2018JA025776 convection; observations; plasmasphere; RBSP; simulation; Van Allen Probes 
2016 
The relationship between the plasmapause and outer belt electrons We quantify the spatial relationship between the plasmapause and outer belt electrons for a 5 day period, 15\textendash20 January 2013, by comparing locations of relativistic electron flux peaks to the plasmapause. A peakfinding algorithm is applied to 1.8\textendash7.7 MeV relativistic electron flux data. A plasmapause gradient finder is applied to wavederived electron number densities >10 cm3. We identify two outer belts. Outer belt 1 is a stable zone of >3 MeV electrons located 1\textendash2 RE inside the plasmapause. Outer belt 2 is a dynamic zone of <3 MeV electrons within 0.5 RE of the moving plasmapause. Electron fluxes earthward of each belt\textquoterights peak are anticorrelated with cold plasma density. Belt 1 decayed on hiss timescales prior to a disturbance on 17 January and suffered only a modest dropout, perhaps owing to shielding by the plasmasphere. Afterward, the partially depleted belt 1 continued to decay at the initial rate. Belt 2 was emptied out by strong disturbancetime losses but restored within 24 h. For global context we use a plasmapause test particle simulation and derive a new plasmaspheric index Fp, the fraction of a circular drift orbit inside the plasmapause. We find that the locally measured plasmapause is (for this event) a good proxy for the globally integrated opportunity for losses in cold plasma. Our analysis of the 15\textendash20 January 2013 time interval confirms that highenergy electron storage rings can persist for weeks or even months if prolonged quiet conditions prevail. This case study must be followed up by more general study (not limited to a 5 day period). Goldstein, J.; Baker, D.; Blake, J.; De Pascuale, S.; Funsten, H.; Jaynes, A.; Jahn, J.M.; Kletzing, C.; Kurth, W.; Li, W.; Reeves, G.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2016 YEAR: 2016 DOI: 10.1002/2016JA023046 Plasmapause; Plasmaspheric Hiss; Radiation belts; simulation; stormtime dropouts; Van Allen Probes 
Multispacecraft Observations and Modeling of the June 22/23, 2015 Geomagnetic Storm The magnetic storm of June 2223, 2015 was one of the largest in the current solar cycle. We present in situ observations from the Magnetospheric Multiscale Mission (MMS) and the Van Allen Probes (VAP) in the magnetotail, fieldaligned currents from AMPERE, and ionospheric flow data from DMSP. Our realtime space weather alert system sent out a \textquotedblleftred alert\textquotedblright, correctly predicting Kp indices greater than 8. We show strong outflow of ionospheric Oxygen, dipolarizations in the MMS magnetometer data, and dropouts in the particle fluxes seen by the MMS FPI instrument suite. At ionospheric altitudes, the AMPERE data show highly variable currents exceeding 20 MA. We present numerical simulations with the BATSRUS global magnetohydrodynamic (MHD) model linked with the Rice Convection Model (RCM). The model predicted the magnitude of the dipolarizations, and varying polar cap convection patterns, which were confirmed by DMSP measurements. Reiff, P.; Daou, A.; Sazykin, S; Nakamura, R.; Hairston, M.; Coffey, V.; Chandler, M.; Anderson, B.; Russell, C.; Welling, D.; Fuselier, S.; Genestreti, K.; Published by: Geophysical Research Letters Published on: 05/2016 YEAR: 2016 DOI: 10.1002/2016GL069154 Dipolarization; Geomagnetic storm; MMS; prediction; simulation; Space weather; Van Allen Probes 
2015 
We perform test particle simulations of energetic electrons interacting with whistler mode chorus emissions. We compute trajectories of a large number of electrons forming a delta function with the same energy and equatorial pitch angle. The electrons are launched at different locations along the magnetic field line and different timings with respect to a pair of chorus emissions generated at the magnetic equator. We follow the evolution of the delta function and obtain a distribution function in energy and equatorial pitch angle, which is a numerical Green\textquoterights function for one cycle of chorus waveparticle interaction. We obtain the Green\textquoterights functions for the energy range 10 keV\textendash6 MeV and all pitch angles greater than the loss cone angle. By taking the convolution integral of the Green\textquoterights functions with the distribution function of the injected electrons repeatedly, we follow a longtime evolution of the distribution function. We find that the energetic electrons are accelerated effectively by relativistic turning acceleration and ultrarelativistic acceleration through nonlinear trapping by chorus emissions. Further, these processes result in the rapid formation of a dumbbell distribution of highly relativistic electrons within a few minutes after the onset of the continuous injection of 10\textendash30 keV electrons. Omura, Yoshiharu; Miyashita, Yu; Yoshikawa, Masato; Summers, Danny; Hikishima, Mitsuru; Ebihara, Yusuke; Kubota, Yuko; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015JA021563 Chorus; nonlinear waveparticle interaction; Particle acceleration; Radiation belts; relativistic electrons; simulation 
Most previous work on nonlinear waveparticle interactions between energetic electrons and VLF waves in the Earth\textquoterights magnetosphere has assumed parallel propagation, the underlying mechanism being nonlinear trapping of cyclotron resonant electrons in a parabolic magnetic field inhomogeneity. Here nonlinear waveparticle interaction in oblique whistlers in the Earth\textquoterights magnetosphere is investigated. The study is nonselfconsistent and assumes an arbitrarily chosen wave field. We employ a \textquotedblleftcontinuous wave\textquotedblright wave field with constant frequency and amplitude, and a model for an individual VLF chorus element. We derive the equations of motion and trapping conditions in oblique whistlers. The resonant particle distribution function, resonant current, and nonlinear growth rate are computed as functions of position and time. For all resonances of order n, resonant electrons obey the trapping equation, and provided the wave amplitude is big enough for the prevailing obliquity, nonlinearity manifests itself by a \textquotedbllefthole\textquotedblright or \textquotedbllefthill\textquotedblright in distribution function, depending on the zeroorder distribution function and on position. A key finding is that the n = 1 resonance is relatively unaffected by moderate obliquity up to 25\textdegree, but growth rates roll off rapidly at high obliquity. The n = 1 resonance saturates due to the adiabatic effect and here reaches a maximum growth at ~20 pT, 2000 km from the equator. Damping due to the n = 0 resonance is not subject to adiabatic effects and maximizes at some 8000 km from the equator at an obliquity ~55\textdegree. Nunn, David; Omura, Yoshiharu; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2015 YEAR: 2015 DOI: 10.1002/2014JA020898 Chorus; nonlinear process; oblique propagation; simulation; Waveparticle interaction; whistler 
2014 
Simulation of Van Allen Probes Plasmapause Encounters We use an E \texttimes Bdriven plasmapause test particle (PTP) simulation to provide global contextual information for in situ measurements by the Van Allen Probes (RBSP) during 15\textendash20 January 2013. During 120 h of simulation time beginning on 15 January, geomagnetic activity produced three plumes. The third and largest simulated plume formed during enhanced convection on 17 January, and survived as a rotating, wrapped, residual plume for tens of hours. To validate the simulation, we compare its output with RBSP data. Virtual RBSP satellites recorded 28 virtual plasmapause encounters during 15\textendash19 January. For 26 of 28 (92\%) virtual crossings, there were corresponding actual RBSP encounters with plasmapause density gradients. The mean difference in encounter time between model and data is 36 min. The mean modeldata difference in radial location is 0:40\textpm0:05 RE. The modeldata agreement is better for strong convection than for quiet or weakly disturbed conditions. On 18 January, both RBSP spacecraft crossed a tenuous, detached plasma feature at approximately the same time and nightside location as a wrapped residual plume, predicted by the model to have formed 32 h earlier on 17 January. The agreement between simulation and data indicates that the modelprovided global information is adequate to correctly interpret the RBSP density observations. Goldstein, J.; De Pascuale, S.; Kletzing, C.; Kurth, W.; Genestreti, K.; Skoug, R.; Larsen, B.; Kistler, L.; Mouikis, C.; Spence, H.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2014 YEAR: 2014 DOI: 10.1002/2014JA020252 observations; plasmasphere; residual plume; simulation; Van Allen Probes 
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