Bibliography

Harmonization of RBSP and Arase energetic electron measurements utilizing ESA radiation monitor data

Abstract Accurate measurements of trapped energetic electron fluxes are of major importance for the studies of the complex nature of radiation belts and the characterization of space radiation environment. The harmonization of measurements between different instruments increase the accuracy of scientific studies and the reliability of data-driven models that treat the specification of space radiation environment. An inter-calibration analysis of the energetic electron flux measurements of the Magnetic Electron Ion Spectrometer (MagEIS) and the Relativistic Electron-Proton Telescope (REPT) instruments on-board the Van Allen Probes (VAP) Mission versus the measurements of the Extremely High Energy Electron Experiment (XEP) unit on-board Arase satellite is presented. The performed analysis demonstrates a remarkable agreement between the majority of MagEIS and XEP measurements and suggests the re-scaling of MagEIS HIGH unit and of REPT measurements for the treatment of flux spectra discontinuities. The proposed adjustments were validated successfully using measurements from ESA Environmental Monitoring Unit (EMU) on-board GSAT0207 and the Standard Radiation Monitor (SREM) on-board INTEGRAL. The derived results lead to the harmonization of science-class experiments on-board VAP (2012-2019) and Arase (2017-) and propose the use of the datasets as reference in a series of space weather and space radiation environment developments.

Sandberg, I.; Jiggens, P.; Evans, H.; Papadimitriou, C.; Aminalragia–Giamini, S.; Katsavrias, Ch.; Boyd, A.; O’Brien, T.; Higashio, N.; Mitani, T.; Shinohara, I.; Miyoshi, Y.; Baker, D.; Daglis, I.;

Published by: Space Weather      Published on: 04/2021

YEAR: 2021     DOI: https://doi.org/10.1029/2020SW002692

Radiation belt; calibration; data harmonization; space radiation environment; energetic electrons; Van Allen Probes

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 in-depth 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 0.9-MeV 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; Wave-particle 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 in-depth 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 0.9-MeV 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; Wave-particle interaction; Plasmapause; Van Allen Probes

Storm Time Depletions of Multi-MeV Radiation Belt Electrons Observed at Different Pitch Angles

During geomagnetic storms, the rapid depletion of the high-energy (several MeV) outer radiation belt electrons is the result of loss to the interplanetary medium through the magnetopause, outward radial diffusion, and loss to the atmosphere due to wave-particle interactions. We have performed a statistical study of 110 storms using pitch angle resolved electron flux measurements from the Van Allen Probes mission and found that inside of the radiation belt (L* = 3 - 5) the number of storms that result in depletion of electrons with equatorial pitch angle αeq = 30o is higher than number of storms that result in depletion of electrons with equatorial pitch angle αeq = 75o. We conclude that this result is consistent with electron scattering by whistler and electromagnetic ion cyclotron waves. At the outer edge of the radiation belt (L* >= 5.2) the number of storms that result in depletion is also large (~40\textendash50\%), emphasizing the significance of the magnetopause shadowing effect and outward radial transport.

Drozdov, A; Aseev, N.; Effenberger, F.; Turner, D.; Saikin, A.; Shprits, Y;

Published by: Journal of Geophysical Research: Space Physics      Published on: 11/2019

YEAR: 2019     DOI: 10.1029/2019JA027332

EMIC waves; multi-MeV electrons; Radiation belts; Van Allen Probes

Evaluation of Plasma Properties From Chorus Waves Observed at the Generation Region

In this study we present an inversion method which provides thermal plasma population parameters from characteristics of chorus emissions only. Our ultimate goal is to apply this method to ground-based data in order to derive the lower-energy boundary condition for many radiation belt models. The first step is to test the chorus inversion method on in situ data of the Van Allen Probes in the generation region. The density and thermal velocity of energetic electrons (few kiloelectron volts to 100 keV) are derived from frequency sweep rate and starting frequencies of chorus emissions through analysis of wave data from the Electric and Magnetic Field Instrument Suite and Integrated Science on board the Van Allen Probes. The nonlinear wave growth theory of Omura and Nunn (2011, https://doi.org/10.1029/2010JA016280) serves as the basis for our inversion method, assuming that the triggering wave is originated by the linear cyclotron instability. We present 16 consecutive rising-tone emissions recorded in the generation region between 11 and 12 UT on 14 November 2012. The results of the inversion are compared with density and thermal velocities (parallel and perpendicular) of energetic electrons derived from the unidirectional flux data of the Helium, Oxygen, Proton, and Electron instrument, showing a good agreement: The normalized root-mean-square deviation between the measured and predicted values are less than \~15\%. We found that the theoretical amplitudes are consistent with the measured ones. The relation between linear and nonlinear wave growth agrees with our basic assumption; namely, linear growth is a preceding process of nonlinear wave growth. We analyze electron distributions at the relativistic resonant energy ranges.

asz, Lilla; Omura, Yoshiharu; Lichtenberger, J\; Friedel, Reinhard;

Published by: Journal of Geophysical Research: Space Physics      Published on: 05/2019

YEAR: 2019     DOI: 10.1029/2018JA026337

chorus inversion; Van Allen Probes; Wave-particle interaction

Electron intensity measurements by the Cluster/RAPID/IES instrument in Earth\textquoterights radiation belts and ring current

The Cluster mission, launched in 2000, has produced a large database of electron flux intensity measurements in the Earth\textquoterights magnetosphere by the Research with Adaptive Particle Imaging Detector (RAPID)/ Imaging Electron Spectrometer (IES) instrument. However, due to background contamination of the data with high-energy electrons (<400 keV) and inner-zone protons (230-630 keV) in the radiation belts and ring current, the data have been rarely used for inner-magnetospheric science. The current paper presents two algorithms for background correction. The first algorithm is based on the empirical contamination percentages by both protons and electrons. The second algorithm uses simultaneous proton observations. The efficiencies of these algorithms are demonstrated by comparison of the corrected Cluster/RAPID/IES data with Van Allen Probes/Magnetic Electron Ion Spectrometer (MagEIS) measurements for 2012-2015. Both techniques improved the IES electron data in the radiation belts and ring current, as the yearly averaged flux intensities of the two missions show the ratio of measurements close to 1. We demonstrate a scientific application of the corrected IES electron data analyzing its evolution during solar cycle. Spin-averaged yearly mean IES electron intensities in the outer belt for energies 40-400 keV at L-shells between 4 and 6 showed high positive correlation with AE index and solar wind dynamic pressure during 2001- 2016. The relationship between solar wind dynamic pressure and IES electron measurements in the outer radiation belt was derived as a uniform linear-logarithmic equation.

Smirnov, A.; Kronberg, E.; Latallerie, F.; Daly, P.; Aseev, N.; Shprits, Y; Kellerman, A.; Kasahara, S.; Turner, D.; Taylor, M.;

Published by: Space Weather      Published on: 02/2019

YEAR: 2019     DOI: 10.1029/2018SW001989

electrons; Radiation belts; Solar Cycle; Space weather; Van Allen Probes

Simulations of Electron Energization and Injection by BBFs Using High-Resolution LFM MHD Fields

We study electron injection and energization by bursty bulk flows (BBFs), by tracing electron trajectories using magnetohydrodynamic (MHD) field output from the Lyon-Fedder-Mobarry (LFM) code. The LFM MHD simulations were performed using idealized solar wind conditions to produce BBFs. We show that BBFs can inject energetic electrons of few to 100 keV from the magnetotatail beyond -24 RE to inward of geosynchronous, while accelerating them in the process. We also show the dependence of energization and injection on the initial relative position of the electrons to the magnetic field structure of the BBF, the initial pitch angle, and the initial energy. In addition, we have shown that the process can be nonadiabatic with violation of the first adiabatic invariant (μ). Further, we discuss the mechanism of energization and injection in order to give generalized insight into the process.

Eshetu, W.; Lyon, J.; Hudson, M.; Wiltberger, M.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 02/2019

YEAR: 2019     DOI: 10.1029/2018JA025789

Van Allen Probes

Pitch Angle Scattering of Energetic Electrons by BBFs

Field line curvature scattering by the magnetic field structure associated with bursty bulk flows (BBFs) has been studied, using simulated output fields from the Lyon-Fedder-Mobarry global magnetohydrodynamic code for specified solar wind input. There are weak magnetic field strength (B) regions adjacent to BBFs observed in the simulations. We show that these regions can cause strong scattering where the first adiabatic invariant changes by several factors within one equatorial crossing of energetic electrons of a few kiloelectron volts when the BBFs are beyond 10RE geocentric in the tail. Scattering by BBFs decreases as they move toward the Earth or when the electron energy decreases. For radiation belt electrons near or inside geosynchronous orbit we demonstrate that the fields associated with BBFs can cause weak scattering where the fractional change of the first invariant (μ0) within one equatorial crossing is small, but the change due to several crossings can accumulate. For the weak scattering case we developed a method of calculating the pitch angle diffusion coefficient Dαα. Dαα for radiation belt electrons for one particular BBF were calculated as a function of initial energy, equatorial pitch angle, and radial location. These Dαα values were compared to calculated Dαα for a dipole field with no electric field. We further compared Dαα values with that of stretched magnetic fields calculated by Artemyev et al. (2013, https://doi.org/10.5194/angeo-31-1485-2013) at r≈7RE. Results show that scattering by BBFs can be comparable to the most highly stretched magnetic field they studied.

Eshetu, W.; Lyon, J.; Hudson, M.; Wiltberger, M.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2018

YEAR: 2018     DOI: 10.1029/2018JA025788

Van Allen Probes

Simulated prompt acceleration of multi-MeV electrons by the 17 March 2015 interplanetary shock

Prompt enhancement of relativistic electron flux at L = 3-5 has been reported from Van Allen Probes Relativistic Electron Proton Telescope (REPT) measurements associated with the 17 March 2015 interplanetary shock compression of the dayside magnetosphere. Acceleration by \~ 1 MeV is inferred on less than a drift time scale as seen in prior shock compression events, which launch a magetosonic azimuthal electric field impulse tailward. This impulse propagates from the dayside around the flanks accelerating electrons in drift resonance at the dusk flank. Such longitudinally localized acceleration events produce a drift echo signature which was seen at >1 MeV energy on both Van Allen Probe spacecraft, with sustained observations by Probe B outbound at L = 5 at 2100 MLT at the time of impulse arrival, measured by the Electric Fields and Waves instrument. MHD-test particle simulations are presented which reproduce drift echo features observed in the REPT measurements at Probe B, including the energy and pitch angle dependence of drift echoes observed. While the flux enhancement was short-lived for this event due to subsequent inward motion of the magnetopause, stronger events with larger electric field impulses, as observed in March 1991 and the Halloween 2003 storm, produce enhancements which can be quantified by the inward radial transport and energization determined by the induction electric field resulting from dayside compression.

Hudson, Mary; Jaynes, Allison; Kress, Brian; Li, Zhao; Patel, Maulik; Shen, Xiaochen; Thaller, Scott; Wiltberger, Michael; Wygant, John;

Published by: Journal of Geophysical Research: Space Physics      Published on: 09/2017

YEAR: 2017     DOI: 10.1002/2017JA024445

17 March 2015; MeV electron acceleration; Radiation belt; test-particle simulation; Van Allen Probes

ULF Wave Analysis and Radial Diffusion Calculation Using a Global MHD Model for the 17 March 2013 and 2015 Storms

The 17 March 2015 St. Patrick\textquoterights Day Storm is the largest geomagnetic storm to date of Solar Cycle 24, with a Dst of -223 nT. The magnetopause moved inside geosynchronous orbit under high solar wind dynamic pressure and strong southward IMF Bz causing loss, however a subsequent drop in pressure allowed for rapid rebuilding of the radiation belts. The 17 March 2013 storm also shows similar effects on outer zone electrons: first a rapid dropout due to inward motion of the magnetopause followed by rapid increase in flux above the pre-storm level early in the recovery phase and a slow increase over the next 12 days. These phases can be seen in temporal evolution of the electron phase space density measured by the ECT instruments on Van Allen Probes. Using the Lyon-Fedder-Mobarry global MHD model driven by upstream solar wind measurements, we simulated both St. Patrick\textquoterights Day 2013 and 2015 events, analyzing LFM electric and magnetic fields to calculate radial diffusion coefficients. These coefficients have been implemented in a radial diffusion code, using the measured electron phase space density following the local heating as the initial radial profile and outer boundary condition for subsequent temporal evolution over the next 12 days, beginning 18 March. Agreement with electron phase space density at 1000 MeV/G measured by the MagEIS component of the ECT instrument suite on Van Allen Probes was much improved using radial diffusion coefficients from the MHD simulations relative to coefficients parametrized by a global geomagnetic activity index.

Li, Zhao; Hudson, Mary; Patel, Maulik; Wiltberger, Michael; Boyd, Alex; Turner, Drew;

Published by: Journal of Geophysical Research: Space Physics      Published on: 06/2017

YEAR: 2017     DOI: 10.1002/2016JA023846

March 2013; March 2015; radial diffusion; Radiation belt; Van Allen Probes

Comparing and contrasting dispersionless injections at geosynchronous orbit during a substorm event

Particle injections in the magnetosphere transport electrons and ions from the magnetotail to the radiation belts. Here we consider generation mechanisms of \textquotedblleftdispersionless\textquotedblright injections, namely, those with simultaneous increase of the particle flux over a wide energy range. In this study we take advantage of multisatellite observations which simultaneously monitor Earth\textquoterights magnetospheric dynamics from the tail toward the radiation belts during a substorm event. Dispersionless injections are associated with instabilities in the plasma sheet during the growth phase of the substorm, with a dipolarization front at the onset and with magnetic flux pileup during the expansion phase. They show different spatial spread and propagation characteristics. Injection associated with the dipolarization front is the most penetrating. At geosynchronous orbit (6.6 RE), the electron distributions do not have a classic power law fit but instead a bump on tail centered on \~120 keV during dispersionless electron injections. However, electron distributions of injections associated with magnetic flux pileup in the magnetotail (13 RE) do not show such a signature. We surmise that an additional resonant acceleration occurs in between these locations. We relate the acceleration mechanism to the electron drift resonance with ultralow frequency waves localized in the inner magnetosphere.

Kronberg, E.; Grigorenko, E.; Turner, D.; Daly, P.; Khotyaintsev, Y.; Kozak, L.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2017

YEAR: 2017     DOI: 10.1002/2016JA023551

Acceleration; current wedge; Dipolarization; particle injections; substorm; ULF waves; Van Allen Probes

Spectra of keV protons related to ion-cyclotron wave packets

We use the Fokker-Planck-Kolmogorov equation to study the statistical aspects of stochastic dynamics of the radiation belt (RB) protons driven by nonlinear electromagnetic ion-cyclotron (EMIC) wave packets. We obtain the spectra of keV protons scattered by these waves that show steeping near the gyroresonance, the signature of resonant wave-particle interaction that cannot be described by a simple power law. The most likely mechanism for proton precipitation events in RBs is shown to be nonlinear wave-particle interaction, namely, the scattering of RB protons into the loss cone by EMIC waves.

Khazanov, K.; Sibeck, D.; Tel\textquoterightnikhin, A.; Kronberg, T.;

Published by: Physics of Plasmas      Published on: 01/2017

YEAR: 2017     DOI: http://dx.doi.org/10.1063/1.4973323

Diffusion; Particle precipitation; protons; Van Allen Probes; wave particle interactions; Wave power

Global ULF wave analysis of radial diffusion coefficients using a global MHD model for the 17 March 2015 storm

The 17\textendash18 March 2015 storm is the largest geomagnetic storm in the Van Allen Probes era to date. The Lyon-Fedder-Mobarry global MHD model has been run for this event using ARTEMIS data as solar wind input. The ULF wave power spectral density of the azimuthal electric field and compressional magnetic field is analyzed in the 0.5\textendash8.3 mHz range. The lowest three azimuthal modes account for 70\% of the total power during quiet times. However, during high activity, they are not exclusively dominant. The calculation of the radial diffusion coefficient is presented. We conclude that the electric field radial diffusion coefficient is dominant over the magnetic field coefficient by one to two orders of magnitude. This result contrasts with the dominant magnetic field diffusion coefficient used in most 3-D diffusion models.

Li, Zhao; Hudson, Mary; Paral, Jan; Wiltberger, Michael; Turner, Drew;

Published by: Journal of Geophysical Research: Space Physics      Published on: 07/2016

YEAR: 2016     DOI: 10.1002/2016JA022508

March 2015; radial diffusion; radial diffusion coefficient; Radiation belt; ULF waves; Van Allen Probes

Magnetohydrodynamic modeling of three Van Allen Probes storms in 2012 and 2013

Coronal mass ejection (CME)-shock compression of the dayside magnetopause has been observed to cause both prompt enhancement of radiation belt electron flux due to inward radial transport of electrons conserving their first adiabatic invariant and prompt losses which at times entirely eliminate the outer zone. Recent numerical studies suggest that enhanced ultra-low frequency (ULF) wave activity is necessary to explain electron losses deeper inside the magnetosphere than magnetopause incursion following CME-shock arrival. A combination of radial transport and magnetopause shadowing can account for losses observed at radial distances into L = 4.5, well within the computed magnetopause location. We compare ULF wave power from the Electric Field and Waves (EFW) electric field instrument on the Van Allen Probes for the 8 October 2013 storm with ULF wave power simulated using the Lyon\textendashFedder\textendashMobarry (LFM) global magnetohydrodynamic (MHD) magnetospheric simulation code coupled to the Rice Convection Model (RCM). Two other storms with strong magnetopause compression, 8\textendash9 October 2012 and 17\textendash18 March 2013, are also examined. We show that the global MHD model captures the azimuthal magnetosonic impulse propagation speed and amplitude observed by the Van Allen Probes which is responsible for prompt acceleration at MeV energies reported for the 8 October 2013 storm. The simulation also captures the ULF wave power in the azimuthal component of the electric field, responsible for acceleration and radial transport of electrons, at frequencies comparable to the electron drift period. This electric field impulse has been shown to explain observations in related studies (Foster et al., 2015) of electron acceleration and drift phase bunching by the Energetic Particle, Composition, and Thermal Plasma Suite (ECT) instrument on the Van Allen Probes.

Paral, J.; Hudson, M.; Kress, B.; Wiltberger, M.; Wygant, J.; Singer, H.;

Published by: Annales Geophysicae      Published on: 08/2015

YEAR: 2015     DOI: 10.5194/angeo-33-1037-2015

MHD; Van Allen Probes

Field-aligned chorus wave spectral power in Earth\textquoterights outer radiation belt

Chorus-type whistler waves are one of the most intense electromagnetic waves generated naturally in the magnetosphere. These waves have a substantial impact on the radiation belt dynamics as they are thought to contribute to electron acceleration and losses into the ionosphere through resonant wave\textendashparticle interaction. Our study is devoted to the determination of chorus wave power distribution on frequency in a wide range of magnetic latitudes, from 0 to 40\textdegree. We use 10 years of magnetic and electric field wave power measured by STAFF-SA onboard Cluster spacecraft to model the initial (equatorial) chorus wave spectral power, as well as PEACE and RAPID measurements to model the properties of energetic electrons (~ 0.1\textendash100 keV) in the outer radiation belt. The dependence of this distribution upon latitude obtained from Cluster STAFF-SA is then consistently reproduced along a certain L-shell range (4 <= L <= 6.5), employing WHAMP-based ray tracing simulations in hot plasma within a realistic inner magnetospheric model. We show here that, as latitude increases, the chorus peak frequency is globally shifted towards lower frequencies. Making use of our simulations, the peak frequency variations can be explained mostly in terms of wave damping and amplification, but also cross-L propagation. These results are in good agreement with previous studies of chorus wave spectral extent using data from different spacecraft (Cluster, POLAR and THEMIS). The chorus peak frequency variations are then employed to calculate the pitch angle and energy diffusion rates, resulting in more effective pitch angle electron scattering (electron lifetime is halved) but less effective acceleration. These peak frequency parameters can thus be used to improve the accuracy of diffusion coefficient calculations.

Breuillard, H.; Agapitov, O.; Artemyev, A.; Kronberg, E.; Haaland, S.; Daly, P.; Krasnoselskikh, V.; Boscher, D.; Bourdarie, S.; Zaliznyak, Y.; Rolland, G.;

Published by: Annales Geophysicae      Published on: 01/2015

YEAR: 2015     DOI: 10.5194/angeo-33-583-2015

Chorus-type whistler waves

Modeling CME-shock driven storms in 2012 - 2013: MHD-test particle simulations

The Van Allen Probes spacecraft have provided detailed observations of the energetic particles and fields environment for CME-shock driven storms in 2012 to 2013 which have now been modeled with MHD-test particle simulations. The Van Allen Probes orbital plane longitude moved from the dawn sector in 2012 to near midnight and pre-noon for equinoctial storms of 2013, providing particularly good measurements of the inductive electric field response to magnetopause compression for the 8 October 2013 CME-shock driven storm. An abrupt decrease in the outer boundary of outer zone electrons coincided with inward motion of the magnetopause for both 17 March and 8 October 2013 storms, as was the case for storms shortly after launch (Hudson et al., 2014). Modeling magnetopause dropout events in 2013 with electric field diagnostics that were not available for storms immediately following launch has improved our understanding of the complex role that ULF waves play in radial transport during such events.

Hudson, M.; Paral, J.; Kress, B.; Wiltberger, M.; Baker, D.; Foster, J.; Turner, D.; Wygant, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 01/2015

YEAR: 2015     DOI: 10.1002/2014JA020833

Van Allen Probes; CME-shock

Near real-time ionospheric monitoring over Europe at the Royal Observatory of Belgium using GNSS data

Various scientific applications and services increasingly demand real-time information on the effects of space weather on Earth\textquoterights atmosphere. In this frame, the Royal Observatory of Belgium (ROB) takes advantage of the dense EUREF Permanent GNSS Network (EPN) to monitor the ionosphere over Europe from the measured delays in the GNSS signals, and provides publicly several derived products. The main ROB products consist of ionospheric vertical Total Electron Content (TEC) maps over Europe and their variability estimated in near real-time every 15 min on 0.5\textdegree \texttimes 0.5\textdegree grids using GPS observations. The maps are available online with a latency of ~3 min in IONEX format at ftp://gnss.oma.be and as interactive web pages at www.gnss.be. This paper presents the method used in the ROB-IONO software to generate the maps. The ROB-TEC maps show a good agreement with widely used post-processed products such as IGS and ESA with mean differences of 1.3 \textpm 0.9 and 0.4 \textpm 1.6 TECu respectively for the period 2012 to mid-2013. In addition, we tested the reliability of the ROB-IONO software to detect abnormal ionospheric activity during the Halloween 2003 ionospheric storm. For this period, the mean differences with IGS and ESA maps are 0.9 \textpm 2.2 and 0.6 \textpm 6.8 TECu respectively with maximum differences (>38 TECu) occurring during the major phase of the storm. These differences are due to the lower resolution in time and space of both IGS and ESA maps compared to the ROB-TEC maps. A description of two recent events, one on March 17, 2013 and one on February 27, 2014 also highlights the capability of the method adopted in the ROB-IONO software to detect in near real-time abnormal ionospheric behaviour over Europe. In that frame, ROB maintains a data base publicly available with identified ionospheric events since 2012.

Bergeot, Nicolas; Chevalier, Jean-Marie; Bruyninx, Carine; Pottiaux, Eric; Aerts, Wim; Baire, Quentin; Legrand, Juliette; Defraigne, Pascale; Huang, Wei;

Published by: Journal of Space Weather and Space Climate      Published on: 09/2014

YEAR: 2014     DOI: 10.1051/swsc/2014028

Ionosphere

Relativistic electron precipitation events driven by electromagnetic ion-cyclotron waves

We adopt a canonical approach to describe the stochastic motion of relativistic belt electrons and their scattering into the loss cone by nonlinear EMIC waves. The estimated rate of scattering is sufficient to account for the rate and intensity of bursty electron precipitation. This interaction is shown to result in particle scattering into the loss cone, forming \~10 s microbursts of precipitating electrons. These dynamics can account for the statistical correlations between processes of energization, pitch angle scattering, and relativistic electron precipitation events, that are manifested on large temporal scales of the order of the diffusion time \~tens of minutes.

Khazanov, G.; Sibeck, D.; Tel\textquoterightnikhin, A.; Kronberg, T.;

Published by: Physics of Plasmas      Published on: 08/2014

YEAR: 2014     DOI: 10.1063/1.4892185

Diffusion; Electron scattering; Nonlinear waves; wave-particle interactions; Whistler waves

Simulated magnetopause losses and Van Allen Probe flux dropouts

Three radiation belt flux dropout events seen by the Relativistic Electron Proton Telescope soon after launch of the Van Allen Probes in 2012 (Baker et al., 2013a) have been simulated using the Lyon-Fedder-Mobarry MHD code coupled to the Rice Convection Model, driven by measured upstream solar wind parameters. MHD results show inward motion of the magnetopause for each event, along with enhanced ULF wave power affecting radial transport. Test particle simulations of electron response on 8 October, prior to the strong flux enhancement on 9 October, provide evidence for loss due to magnetopause shadowing, both in energy and pitch angle dependence. Severe plasmapause erosion occurred during ~ 14 h of strongly southward interplanetary magnetic field Bz beginning 8 October coincident with the inner boundary of outer zone depletion.

Hudson, M.; Baker, D.; Goldstein, J.; Kress, B.; Paral, J.; Toffoletto, F.; Wiltberger, M.;

Published by: Geophysical Research Letters      Published on: 02/2014

YEAR: 2014     DOI: 10.1002/2014GL059222

Van Allen Probes

The Electric Field and Waves (EFW) Instruments on the Radiation Belt Storm Probes Mission

The Electric Fields and Waves (EFW) Instruments on the two Radiation Belt Storm Probe (RBSP) spacecraft (recently renamed the Van Allen Probes) are designed to measure three dimensional quasi-static and low frequency electric fields and waves associated with the major mechanisms responsible for the acceleration of energetic charged particles in the inner magnetosphere of the Earth. For this measurement, the instrument uses two pairs of spherical double probe sensors at the ends of orthogonal centripetally deployed booms in the spin plane with tip-to-tip separations of 100 meters. The third component of the electric field is measured by two spherical sensors separated by \~15 m, deployed at the ends of two stacer booms oppositely directed along the spin axis of the spacecraft. The instrument provides a continuous stream of measurements over the entire orbit of the low frequency electric field vector at 32 samples/s in a survey mode. This survey mode also includes measurements of spacecraft potential to provide information on thermal electron plasma variations and structure. Survey mode spectral information allows the continuous evaluation of the peak value and spectral power in electric, magnetic and density fluctuations from several Hz to 6.5 kHz. On-board cross-spectral data allows the calculation of field-aligned wave Poynting flux along the magnetic field. For higher frequency waveform information, two different programmable burst memories are used with nominal sampling rates of 512 samples/s and 16 k samples/s. The EFW burst modes provide targeted measurements over brief time intervals of 3-d electric fields, 3-d wave magnetic fields (from the EMFISIS magnetic search coil sensors), and spacecraft potential. In the burst modes all six sensor-spacecraft potential measurements are telemetered enabling interferometric timing of small-scale plasma structures. In the first burst mode, the instrument stores all or a substantial fraction of the high frequency measurements in a 32 gigabyte burst memory. The sub-intervals to be downloaded are uplinked by ground command after inspection of instrument survey data and other information available on the ground. The second burst mode involves autonomous storing and playback of data controlled by flight software algorithms, which assess the \textquotedbllefthighest quality\textquotedblright events on the basis of instrument measurements and information from other instruments available on orbit. The EFW instrument provides 3-d wave electric field signals with a frequency response up to 400 kHz to the EMFISIS instrument for analysis and telemetry (Kletzing et al. Space Sci. Rev. 2013).

Wygant, J.; Bonnell, J; Goetz, K.; Ergun, R.E.; Mozer, F.; Bale, S.D.; Ludlam, M.; Turin, P.; Harvey, P.R.; Hochmann, R.; Harps, K.; Dalton, G.; McCauley, J.; Rachelson, W.; Gordon, D.; Donakowski, B.; Shultz, C.; Smith, C.; Diaz-Aguado, M.; Fischer, J.; Heavner, S.; Berg, P.; Malaspina, D.; Bolton, M.; Hudson, M.; Strangeway, R.; Baker, D.; Li, X.; Albert, J.; Foster, J.C.; Chaston, C.C.; Mann, I.; Donovan, E.; Cully, C.M.; Cattell, C.; Krasnoselskikh, V.; Kersten, K.; Brenneman, A; Tao, J.;

Published by: Space Science Reviews      Published on: 11/2013

YEAR: 2013     DOI: 10.1007/s11214-013-0013-7

RBSP; Van Allen Probes

Radiation belt 2D and 3D simulations for CIR-driven storms during Carrington Rotation 2068

As part of the International Heliospheric Year, the Whole Heliosphere Interval, Carrington Rotation 2068, from March 20 to April 16, 2008 was chosen as an internationally coordinated observing and modeling campaign. A pair of solar wind structures identified as Corotating Interaction Regions (CIR), characteristic of the declining phase of the solar cycle and solar minimum, was identified in solar wind plasma measurements from the ACE satellite. Such structures have previously been determined to be geoeffective in producing enhanced outer zone radiation belt electron fluxes, on average greater than at solar maximum. MHD fields from the Coupled Magnetosphere\textendashIonosphere\textendashThermosphere (CMIT) model driven by ACE solar wind measurements at L1 have been used to drive both 2D and 3D weighted test particle simulations of electron dynamics for the CIR subset of the month-long CMIT fields. Dropout in electron flux at geosynchronous orbit and enhancement during recovery phase, characteristic of CIR-driven storms, is seen in these moderate (Dstmin=-56, -33 nT) events, while the two CIRs were characterized by increased solar wind velocity in the 650\textendash750 km/s range. The first beginning March 26 produced a greater enhancement in IMF Bz southward and stronger magnetospheric convection, leading to a greater radiation belt electron response at GOES. This study provides the first comparison of 2D and 3D particle dynamics in MHD simulation fields, incorporating the additional diffusive feature of Shebansky orbit trapping of electrons in the magnetic minima on the dayside above and below the equatorial plane. Overall loss occurs during the main phase for 2D and 3D simulations, while incorporation of plasmasheet injection in 2D runs produces a moderate enhancement for the March 26\textendash30 storm, less than observed at GOES, and recovery to initial flux levels as seen for the April 4\textendash7 storm.

Hudson, M.; Brito, Thiago; Elkington, Scot; Kress, Brian; Li, Zhao; Wiltberger, Mike;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: 07/2012

YEAR: 2012     DOI: 10.1016/j.jastp.2012.03.017

Magnetosphere; Modeling; Radiation belts; Solar wind

Radial diffusion and MHD particle simulations of relativistic electron transport by ULF waves in the September 1998 storm

In an MHD particle simulation of the September 1998 magnetic storm the evolution of the radiation belt electron radial flux profile appears to be diffusive, and diffusion caused by ULF waves has been invoked as the probable mechanism. In order to separate adiabatic and nonadiabatic effects and to investigate the radial diffusion mechanism during this storm, in this work we solve a radial diffusion equation with ULF wave diffusion coefficients and a time-dependent outer boundary condition, and the results are compared with the phase space density of the MHD particle simulation. The diffusion coefficients include contributions from both symmetric resonance modes (ω ≈ mωd, where ω is the wave frequency, m is the azimuthal wave number, and ωd is the bounce-averaged drift frequency) and asymmetric resonance modes (ω ≈ (m \textpm 1)ωd). ULF wave power spectral densities are obtained from a Fourier analysis of the electric and magnetic fields of the MHD simulation and are used in calculating the radial diffusion coefficients. The asymmetric diffusion coefficients are proportional to the magnetic field asymmetry, which is also calculated from the MHD field. The resulting diffusion coefficients vary with the radial coordinate L (the Roederer L-value) and with time during different phases of the storm. The last closed drift shell defines the location of the outer boundary. Both the location of the outer boundary and the value of the phase space density at the outer boundary are time-varying. The diffusion calculation simulates a 42-hour period during the 24\textendash26 September 1998 magnetic storm, starting just before the storm sudden commencement and ending in the late recovery phase. The differential flux calculated in the MHD particle simulation is converted to phase space density. Phase space densities in both simulations (diffusion and MHD particle) are functions of Roederer L-value for fixed first and second adiabatic invariants. The Roederer L-value is calculated using drift shell tracing in the MHD magnetic field, and particles have zero second invariant. The radial diffusion calculation reproduces the main features of the MHD particle simulation quite well. The symmetric resonance modes dominate the radial diffusion, especially in the inner and middle L region, while the asymmetric resonances are more important in the outer region. Using both symmetric and asymmetric terms gives a better result than using only one or the other and is better than using a simple power law diffusion coefficient. We find that it is important to specify the value of the phase space density on the outer boundary dynamically in order to get better agreement between the radial diffusion simulation and the MHD particle simulation.

Fei, Yue; Chan, Anthony; Elkington, Scot; Wiltberger, Michael;

Published by: Journal of Geophysical Research      Published on: 12/2006

YEAR: 2006     DOI: 10.1029/2005JA011211

Radial Transport

MHD/particle simulations of radiation belt dynamics

Particle fluxes in the outer radiation belts can show substantial variation in time, over scales ranging from a few minutes, such as during the sudden commencement phase of geomagnetic storms, to the years-long variations associated with the progression of the solar cycle. As the energetic particles comprising these belts can pose a hazard to human activity in space, considerable effort has gone into understanding both the source of these particles and the physics governing their dynamical behavior. Computationally tracking individual test particles in a model magnetosphere represents a very direct, physically-based approach to modeling storm-time radiation belt dynamics. Using global magnetohydrodynamic models of the Earth\textendashSun system coupled with test particle simulations of the radiation belts, we show through two examples that such simulations are capable of capturing the outer zone radiation belt configuration at a variety of time scales and through all phases of a geomagnetic storm. Such simulations provide a physically-based method of investigating the dynamics of the outer radiation zone, and hold promise as a viable method of providing global nowcasts of the radiation environment during geomagnetically active periods.

ELKINGTON, S; Hudson, M.; Wiltberger, M.J; Lyon, J.;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: 04/2002

YEAR: 2002     DOI: 10.1016/S1364-6826(02)00018-4

Shock-Induced Transport. Slot Refilling and Formation of New Belts.

Simulation of Radiation Belt Dynamics Driven by Solar Wind Variations

The rapid rise of relativistic electron fluxes inside geosynchronous orbit during the January 10-11, 1997, CME-driven magnetic cloud event has been simulated using a relativistic guiding center test particle code driven by out-put from a 3D global MHD simulation of the event. A comparison can be made of this event class, characterized by a moderate solar wind speed (< 600 km/s), and those commonly observed at the last solar maximum with a higher solar wind speed and shock accelerated solar energetic proton component. Relativistic electron flux increase occurred over several hours for the January event, during a period of prolonged southward IMF Bz more rapidly than the 1-2 day delay typical of flux increases driven by solar wind high speed stream interactions. Simulations of the January event captured the flux

Hudson, M.; Elkington, S.; Lyon, J.; Goodrich, C.; Rosenberg, T.;

Published by:       Published on:

YEAR: 1999     DOI: 10.1029/GM10910.1029/GM109p0171