Bibliography

Local time distributions of repetition periods for rising tone lower band chorus waves in the magnetosphere

Whistler mode chorus waves generally occur outside the plasmapause in the magnetosphere. The most striking feature of the waves is their occurrence in discrete elements. One of the parameters that describe the discrete elements is the repetition period (Trp), the time between consecutive elements. The Trp has not been studied statistically before. We use high-resolution waveform data to derive distributions of Trp for different local times. We find that the average Trp for the nightside (0.56 s) and dawnside (0.53 s) are smaller than those for the dayside (0.81 s) and duskside (0.97 s). Through a comparison with the background plasma and magnetic fields, we also find that the total magnetic field and temperature are the main controlling factors that affect the variability of Trp. These results are important for understanding the generation mechanism of chorus and choosing parameters in simulations that model the acceleration and loss of electrons by wave-particle interactions.

Shue, Jih-Hong; Hsieh, Yi-Kai; W. Y. Tam, Sunny; Wang, Kaiti; Fu, Hui; Bortnik, Jacob; Tao, Xin; Hsieh, Wen-Chieh; Pi, Gilbert;

Published by: Geophysical Research Letters      Published on: 10/2015

YEAR: 2015     DOI: 10.1002/2015GL066107

Chorus; local time distribution; repetition period

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

Extreme geomagnetic disturbances due to shocks within CMEs

We report on features of solar wind-magnetosphere coupling elicited by shocks propagating through coronal mass ejections (CMEs) by analyzing the intense geomagnetic storm of 6 August 1998. During this event, the dynamic pressure enhancement at the shock combined with a simultaneous increase in the southward component of the magnetic field resulted in a large earthward retreat of Earth\textquoterights magnetopause, which remained close to geosynchronous orbit for more than 4 h. This occurred despite the fact that both shock and CME were weak and relatively slow. Another similar example of a weak shock inside a slow CME resulting in an intense geomagnetic storm is the 30 September 2012 event, which strongly depleted the outer radiation belt. We discuss the potential of shocks inside CMEs to cause large geomagnetic effects at Earth, including magnetopause shadowing.

Lugaz, N.; Farrugia, C.; Huang, C.-L.; Spence, H.;

Published by: Geophysical Research Letters      Published on: 06/2015

YEAR: 2015     DOI: 10.1002/2015GL064530

coronal mass ejections; Geomagnetic storm; magnetopause; magnetosheath; shocks

Van Allen probes, NOAA, GOES, and ground observations of an intense EMIC wave event extending over 12 hours in MLT

Although most studies of the effects of EMIC waves on Earth\textquoterights outer radiation belt have focused on events in the afternoon sector in the outer plasmasphere or plume region, strong magnetospheric compressions provide an additional stimulus for EMIC wave generation across a large range of local times and L shells. We present here observations of the effects of a wave event on February 23, 2014 that extended over 8 hours in UT and over 12 hours in local time, stimulated by a gradual 4-hour rise and subsequent sharp increases in solar wind pressure. Large-amplitude linearly polarized hydrogen band EMIC waves (up to 25 nT p-p) appeared for over 4 hours at both Van Allen Probes, from late morning through local noon, when these spacecraft were outside the plasmapause, with densities ~5-20 cm-3. Waves were also observed by ground-based induction magnetometers in Antarctica (near dawn), Finland (near local noon), Russia (in the afternoon), and in Canada (from dusk to midnight). Ten passes of NOAA-POES and METOP satellites near the northern footpoint of the Van Allen Probes observed 30-80 keV subauroral proton precipitation, often over extended L shell ranges; other passes identified a narrow L-shell region of precipitation over Canada. Observations of relativistic electrons by the Van Allen Probes showed that the fluxes of more field-aligned and more energetic radiation belt electrons were reduced in response to both the emission over Canada and the more spatially extended emission associated with the compression, confirming the effectiveness of EMIC-induced loss processes for this event.

Engebretson, M.; Posch, J.; Wygant, J.; Kletzing, C.; Lessard, M.; Huang, C.-L.; Spence, H.; Smith, C.; Singer, H.; Omura, Y.; Horne, R.; Reeves, G.; Baker, D.; Gkioulidou, M.; Oksavik, K.; Mann, I.; Raita, T; Shiokawa, K.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 06/2015

YEAR: 2015     DOI: 10.1002/2015JA021227

EMIC waves; magnetospheric compressions; Radiation belts; Van Allen Probes

3D test-particle simulation of the 17-18 March, 2013 CME-shock driven storm

D test-particle simulation of energetic electrons (hundreds of keV to MeV), including both an initially trapped population and continuously injected population, driven by the Lyon-Fedder-Mobarry (LFM) global MHD model coupled with Magnetosphere-Ionosphere Coupler/Solver (MIX) boundary conditions, is performed for the March 17, 2013 storm. The electron trajectories are calculated and weighted using the ESA model for electron flux vs. energy and L. The simulation captures the flux dropout at both GOES-13 and GOES-15 locations after a strong CME-shock arrival which produced a Dst=-132 nT storm, and recovery to the pre-storm value later, consistent with GOES satellite measurements. This study provides the first 3D test-particle simulation combining the trapped and injected populations. The result demonstrates that including both populations in the simulation is essential to study the dynamics of the outer radiation belt over the typical day-long timescale of ring current development, main phase and early recovery phase.

Li, Zhao; Hudson, Mary; Kress, Brian; Paral, Jan;

Published by: Geophysical Research Letters      Published on: 06/2015

YEAR: 2015     DOI: 10.1002/2015GL064627

17 March; 2013; CME-shock driven storm; Radiation belt; test-particle simulation

The enhancement of cosmic radio noise absorption due to hiss-driven energetic electron precipitation during substorms

The Van-Allen probes, low-altitude NOAA satellite, MetOp satellite and riometer are used to analyze variations of precipitating energetic electron fluxes and cosmic radio noise absorption (CNA) driven by plasmaspheric hiss with respect to geomagnetic activities. The hiss-driven energetic electron precipitations (at L~4.7-5.3, MLT~8-9) are observed during geomagnetic quiet condition and substorms, respectively. We find that the CNA detected by riometers increased very little in the hiss-driven event during quiet condition on September 06, 2012. The hiss-driven enhancement of riometer was still little during the first substorm on September 30, 2012. However, the absorption detected by the riometer largely increased while the energies of the injected electrons became higher during the second substorm on September 30, 2012. The enhancement of CNA (ΔCNA) observed by the riometer and calculated with precipitating energetic electrons are in agreement during the second substorm, implying that the precipitating energetic electrons increase CNA to an obviously detectable level of the riometer during the second substorm on September 30, 2012. The conclusion is consistent with Rodger et al. (2012), which suggests that the higher level of ΔCNA prefer to occur in the substorms, because substorms may produce more intense energetic electron precipitation associated with electron injection. Furthermore, the combination of the observations and theory calculations also suggests that higher-energy electron (>55 keV) precipitation contribute more to the ΔCNA than the lower-energy electron precipitation. In this paper, the higher-energy electron precipitation is related to lower-frequency hiss.

Li, Haimeng; Yuan, Zhigang; Yu, Xiongdong; Huang, Shiyong; Wang, Dedong; Wang, Zhenzhen; Qiao, Zheng; Wygant, John;

Published by: Journal of Geophysical Research: Space Physics      Published on: 06/2015

YEAR: 2015     DOI: 10.1002/2015JA021113

cosmic radio noise absorption; energetic electron precipitation; hiss; substorm; Van Allen Probes

Statistical characteristic of EMIC waves: Van Allen Probe observations

Utilizing the data from the magnetometer instrument which is a part of the Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) instrument suite onboard the Van Allen Probe A from Sep. 2012 to Apr. 2014, when the apogee of the satellite has passed all the MLT sectors, we obtain the statistical distribution characteristic of EMIC waves in the inner magnetosphere over all local times from L=3 to L=6. Compared with the previous statistical results about EMIC waves, the occurrence rates of EMIC waves distribute relatively uniform in the MLT sectors in lower L-shells. On the other hand, in higher L-shells, there are indeed some peaks of the occurrence rate for the EMIC waves, especially in the noon, dusk and night sectors. EMIC waves appear at lower L-shells in the dawn sector than in other sectors. In the lower L-shells (L<4), the occurrence rates of EMIC waves are significant in the dawn sector. This phenomenon may result from the distribution characteristic of the plasmasphere. The location of the plasmapause is usually lower in the dawn sector than that in other sectors, and the plasmapause is considered to be the favored region for the generation of EMIC waves. In higher L-shells (L>4) the occurrence rates of EMIC waves are most significant in the dusk sector, implying the important role of the plasmapause or plasmaspheric plume in generating EMIC waves. We have also investigated the distribution characteristics of the hydrogen band and the helium band EMIC waves. Surprisingly, in the inner magnetosphere, the hydrogen band EMIC waves occur more frequently than the helium band EMIC waves. Both them have peaks of occurrence rate in noon, dusk and night sectors, and the hydrogen band EMIC waves have more obvious peaks than the helium band EMIC waves in the night sector, while the helium band EMIC waves are more concentrated than the hydrogen band EMIC waves in the dusk sector. Both them occur significantly in the noon sector, which implies the important role of the solar wind dynamic pressure.

Wang, Dedong; Yuan, Zhigang; Yu, Xiongdong; Deng, Xiaohua; Zhou, Meng; Huang, Shiyong; Li, Haimeng; Wang, Zhenzhen; Qiao, Zheng; Kletzing, C.; Wygant, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 05/2015

YEAR: 2015     DOI: 10.1002/2015JA021089

distribution; EMIC waves; plasmasphere; Van Allen Probes

One- and two-dimensional hybrid simulations of whistler mode waves in a dipole field

We simulate whistler mode waves using a hybrid code. There are four species in the simulations, hot electrons initialized with a bi-Maxwellian distribution with temperature in the direction perpendicular to background magnetic field greater than that in the parallel direction, warm isotropic electrons, cold inertialess fluid electrons, and protons as an immobile background. The density of the hot population is a small fraction of the total plasma density. Comparison between the dispersion relation of our model and other dispersion relations shows that our model is more accurate for lower frequency whistlers than for higher frequency whistlers. Simulations in 2-D Cartesian coordinates agree very well with those using a full dynamics code. In the 1-D simulations along the dipole magnetic field, the predicted frequency and wave number are observed. Rising tones are observed in the one-fourteenth scale simulations that have larger than realistic magnetic field spatial inhomogeneity. However, in the full-scale 1-D simulation in a dipole field, the waves are more broadband and do not exhibit rising tones. In the 2-D simulations in a meridional plane, the waves are generated with propagation approximately parallel to the background magnetic field. However, the wavefronts become oblique as they propagate to higher latitudes. Simulations with different plasma density profiles across L shell are performed to study the effect of the background density on whistler propagation.

Wu, S.; Denton, R.; Liu, K.; Hudson, M.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2015

YEAR: 2015     DOI: 10.1002/2014JA020736

hybrid simulation; particle-in-cell simulation; plasma waves; Whistler waves

Simulation of ULF wave modulated radiation belt electron precipitation during the 17 March 2013 storm

Balloon-borne instruments detecting radiation belt precipitation frequently observe oscillations in the mHz frequency range. Balloons measuring electron precipitation near the poles in the 100 keV to 2.5 MeV energy range, including the MAXIS, MINIS, and most recently the BARREL balloon experiments, have observed this modulation at ULF wave frequencies [e.g. Foat et al., 1998; Millan et al., 2002; Millan, 2011]. Although ULF waves in the magnetosphere are seldom directly linked to increases in electron precipitation since their oscillation periods are much larger than the gyroperiod and the bounce period of radiation belt electrons, test particle simulations show that this interaction is possible [Brito et al., 2012]. 3D simulations of radiation belt electrons were performed to investigate the effect of ULF waves on precipitation. The simulations track the behavior of energetic electrons near the loss cone, using guiding center techniques, coupled with an MHD simulation of the magnetosphere, using the LFM code, during a CME-shock event on 17 March 2013. Results indicate that ULF modulation of precipitation occurs even without the presence of EMIC waves, which are not resolved in the MHD simulation. The arrival of a strong CME-shock, such as the one simulated, disrupts the electric and magnetic fields in the magnetosphere and causes significant changes in both components of momentum, pitch angle and L-shell of radiation belt electrons, which may cause them to precipitate into the loss cone.

Brito, T.; Hudson, M.; Kress, B.; Paral, J.; Halford, A.; Millan, R.; Usanova, M.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2015

YEAR: 2015     DOI: 10.1002/2014JA020838

precipitation; Radiation belts; Ulf; ULF modulation

BARREL observations of an ICME-Shock impact with the magnetosphere and the resultant radiation belt electron loss.

The Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) mission of opportunity working in tandem with the Van Allen Probes was designed to study the loss of radiation belt electrons to the ionosphere and upper atmosphere. BARREL is also sensitive to X-rays from other sources. During the second BARREL campaign the Sun produced an X-class flare followed by a solar energetic particle event (SEP) associated with the same active region. Two days later on 9 January 2014 the shock generated by the coronal mass ejection (CME) originating from the active region hit the Earth while BARREL was in a close conjunction with the Van Allen Probes. Time History Events and Macroscale Interactions during Substorms (THEMIS) observed the impact of the ICME-shock near the magnetopause, and the Geostationary Operational Environmental Satellite (GOES) satellites were on either side of the BARREL/Van Allen Probe array. The solar interplanetary magnetic field was not ideally oriented to cause a significant geomagnetic storm, but compression from the shock impact led to the loss of radiation belt electrons. We propose that an azimuthal electric field impulse generated by magnetopause compression caused inward electron transport and minimal loss. This process also drove chorus waves, which were responsible for most of the precipitation observed outside the plasmapause. Observations of hiss inside the plasmapause explains the absence of loss at this location. ULF waves were found to be correlated withthe structure of the precipitation. We demonstrate how BARREL can monitor precipitation following a ICME-shock impact at Earth in a cradle-to-grave view; from flare, to SEP, to electron precipitation.

Halford, A.; McGregor, S.; Murphy, K.; Millan, R.; Hudson, M.; Woodger, L.; Cattel, C.; Breneman, A.; Mann, I.; Kurth, W.; Hospodarsky, G.; Gkioulidou, M.; Fennell, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2015

YEAR: 2015     DOI: 10.1002/2014JA020873

BARREL; Van Allen Probes

Disappearance of plasmaspheric hiss following interplanetary shock

Plasmaspheric hiss is one of the important plasma waves controlling radiation belt dynamics. Its spatiotemporal distribution and generation mechanism are presently the object of active research. We here give the first report on the shock-induced disappearance of plasmaspheric hiss observed by the Van Allen Probes on 8 October 2013. This special event exhibits the dramatic variability of plasmaspheric hiss and provides a good opportunity to test its generation mechanisms. The origination of plasmaspheric hiss from plasmatrough chorus is suggested to be an appropriate prerequisite to explain this event. The shock increased the suprathermal electron fluxes, and then the enhanced Landau damping promptly prevented chorus waves from entering the plasmasphere. Subsequently, the shrinking magnetopause removed the source electrons for chorus, contributing significantly to the several-hours-long disappearance of plasmaspheric hiss.

Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Shen, Chao; Zhang, Min; Wang, Shui; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Wygant, J.;

Published by: Geophysical Research Letters      Published on: 03/2015

YEAR: 2015     DOI: 10.1002/2015GL063906

Cyclotron instability; Cyclotron resonance; interplanetary shock; Landau damping; Plasmaspheric Hiss; Radiation belt; Van Allen Probes

In situ observations of EMIC waves in O ⁺ band by the Van Allen Probe A

Through polarization and spectra analysis of the magnetic field observed by the Van Allen Probe A, we present two typical cases of O+ band EMIC waves in the outer plasmasphere or plasma trough. Although such O+ band EMIC waves are rarely observed, 18 different events of O+ band EMIC waves (16 events in the outer plasmasphere and 2 events in the plasma trough) are found from September 2012 to August 2014 with observations of the Van Allen Probe A. We find that the preferred region for the occurrence of O+ band EMIC waves is in L = 2-5 and MLT = 03-13, 19-20, which is in accordance with the occurrence region of O+ ion torus. Therefore, our result suggests that the O+ ion torus in the outer plasmasphere during geomagnetic activities should play an important role in the generation of EMIC waves in O+ band.

Yu, Xiongdong; Yuan, Zhigang; Wang, Dedong; Li, Haimeng; Huang, Shiyong; Wang, Zhenzhen; Zheng, Qiao; Zhou, Mingxia; Kletzing, C.; Wygant, J.;

Published by: Geophysical Research Letters      Published on: 02/2015

YEAR: 2015     DOI: 10.1002/2015GL063250

EMIC waves; O+ ion torus; oxygen band; Van Allen Probes

Plasmatrough exohiss waves observed by Van Allen Probes: Evidence for leakage from plasmasphere and resonant scattering of radiation belt electrons

Exohiss waves are whistler mode hiss observed in the plasmatrough region. We present a case study of exohiss waves and the corresponding background plasma distributions observed by the Van Allen Probes in the dayside low-latitude region. The analysis of wave Poynting fluxes, suprathermal electron fluxes and cold electron densities supports the scenario that exohiss leaks from the plasmasphere into the plasmatrough. Quasilinear calculations further reveal that exohiss can potentially cause the resonant scattering loss of radiation belt electrons ~

Zhu, Hui; Su, Zhenpeng; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Shen, Chao; Xian, Tao; Wang, Shui; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.;

Published by: Geophysical Research Letters      Published on: 02/2015

YEAR: 2015     DOI: 10.1002/2014GL062964

Cyclotron resonance; Exohiss; Landau damping; Plasmaspheric Hiss; Radiation belt electron loss; Van Allen Probes

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

Shock-Induced Prompt Relativistic Electron Acceleration In the Inner Magnetosphere

We present twin Van Allen Probes spacecraft observations of the effects of a solar wind shock impacting the magnetosphere on 8 October 2013. The event provides details both of the accelerating electric fields associated with the shock and the response of inner magnetosphere electron populations across a broad range of energies. During this period the two Van Allen Probes observed shock effects from the vantage point of the dayside magnetosphere at radial positions of L=3 and L=5, at the location where shock-induced acceleration of relativistic electrons occurs. The extended (~1 min) duration of the accelerating electric field across a broad extent of the dayside magnetosphere, coupled with energy dependent relativistic electron gradient drift velocities, selects a preferred range of energies (3 \textendash 4 MeV) for the initial enhancement. Those electrons—whose drift velocity closely matches the azimuthal phase velocity of the shock-induced pulse— stayed in the accelerating wave as it propagated tailward and received the largest increase in energy. Drift resonance with subsequent strong ULF waves further accentuated this range of electron energies. Phase space density and positional considerations permit identification of the source population of the energized electrons. Observations detail the promptness (<20 min), energy range (1.5-4.5 MeV), energy increase (~500 keV), and spatial extent (L*~3.5-4.0) of the enhancement of the relativistic electrons. Prompt acceleration by impulsive shock-induced electric fields and subsequent ULF wave processes therefore comprises a significant mechanism for the acceleration of highly relativistic electrons deep inside the outer radiation belt as shown clearly by this event.

Foster, J.; Wygant, J.; Hudson, M.; Boyd, A.; Baker, D.; Erickson, P.; Spence, H.;

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

YEAR: 2015     DOI: 10.1002/2014JA020642

Van Allen Probes

Wave normal angles of whistler-mode chorus rising and falling tones

We present a study of wave normal angles (θk) of whistler mode chorus emission as observed by Time History of Events and Macroscale Interactions during Substorms (THEMIS) during the year 2008. The three inner THEMIS satellites THA, THD, and THE usually orbit Earth close to the dipole magnetic equator (\textpm20\textdegree), covering a large range of L shells from the plasmasphere out to the magnetopause. Waveform measurements of electric and magnetic fields enable a detailed polarization analysis of chorus below 4 kHz. When displayed in a frequency-θk histogram, four characteristic regions of occurrence are evident. They are separated by gaps at f/fc,e≈0.5 (f is the chorus frequency, fc,e is the local electron cyclotron frequency) and at θk\~40\textdegree. Below θk\~40\textdegree, the average value for θk is predominantly field aligned, but slightly increasing with frequency toward half of fc,e (θk up to 20\textdegree). Above half of fc,e, the average θk is again decreasing with frequency. Above θk\~40\textdegree, wave normal angles are usually close to the resonance cone angle. Furthermore, we present a detailed comparison of electric and magnetic fields of chorus rising and falling tones. Falling tones exhibit peaks in occurrence solely for θk>40\textdegree and are propagating close to the resonance cone angle. Nevertheless, when comparing rising tones to falling tones at θk>40\textdegree, the ratio of magnetic to electric field shows no significant differences. Thus, we conclude that falling tones are generated under similar conditions as rising tones, with common source regions close to the magnetic equatorial plane.

Taubenschuss, Ulrich; Khotyaintsev, Yuri; ik, Ondrej; Vaivads, Andris; Cully, Christopher; Le Contel, Olivier; Angelopoulos, Vassilis;

Published by: Journal of Geophysical Research: Space Physics      Published on: 12/2014

YEAR: 2014     DOI: 10.1002/2014JA020575

Chorus; wave normal

Investigation of EMIC wave scattering as the cause for the BARREL January 17, 2013 relativistic electron precipitation event: a quantitative comparison of simulation with observations

Electromagnetic ion cyclotron (EMIC) waves were observed at multiple observatory locations for several hours on 17 January 2013. During the wave activity period, a duskside relativistic electron precipitation (REP) event was observed by one of the BARREL balloons, and was magnetically mapped close to GOES-13. We simulate the relativistic electron pitch-angle diffusion caused by gyroresonant interactions with EMIC waves using wave and particle data measured by multiple instruments on board GOES-13 and the Van Allen Probes. We show that the count rate, the energy distribution and the time variation of the simulated precipitation all agree very well with the balloon observations, suggesting that EMIC wave scattering was likely the cause for the precipitation event. The event reported here is the first balloon REP event with closely conjugate EMIC wave observations, and our study employs the most detailed quantitative analysis on the link of EMIC waves with observed REP to date.

Li, Zan; Millan, Robyn; Hudson, Mary; Woodger, Leslie; Smith, David; Chen, Yue; Friedel, Reiner; Rodriguez, Juan; Engebretson, Mark; Goldstein, Jerry; Fennell, Joseph; Spence, Harlan;

Published by: Geophysical Research Letters      Published on: 12/2014

YEAR: 2014     DOI: 10.1002/2014GL062273

BARREL; EMIC waves; GOES; pitch angle diffusion; RBSP; relativistic electron precipitation; Van Allen Probes

Quantifying the relative contributions of substorm injections and chorus waves to the rapid outward extension of electron radiation belt

We study the rapid outward extension of the electron radiation belt on a timescale of several hours during three events observed by RBSP and THEMIS satellites, and particularly quantify the contributions of substorm injections and chorus waves to the electron flux enhancement near the outer boundary of radiation belt. A comprehensive analysis including both observations and simulations is performed for the first event on 26 May 2013. The outer boundary of electron radiation belt moved from L = 5.5 to L > 6.07 over about 6 hours, with up to four orders of magnitude enhancement in the 30 keV-5 MeV electron fluxes at L = 6. The observations show that the substorm injection can cause 100\% and 20\% of the total subrelativistic (~0.1 MeV) and relativistic (2-5 MeV) electron flux enhancements within a few minutes. The data-driven simulation supports that the strong chorus waves can yield 60\%-80\% of the total energetic (0.2-5.0 MeV) electron flux enhancement within about 6 hours. Some simple analyses are further given for the other two events on 2 and 29 June 2013, in which the contributions of substorm injections and chorus waves are shown to be qualitatively comparable to those for the first event. These results clearly illustrate the respective importance of substorm injections and chorus waves for the evolution of radiation belt electrons at different energies on a relatively short timescale.

Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; Zong, Q.-G.; He, Zhaoguo; Shen, Chao; Zhang, Min; Wang, Shui; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 12/2014

YEAR: 2014     DOI: 10.1002/2014JA020709

Chorus wave; Electron acceleration; Radiation belt; substorm injection; Van Allen Probes; Wave-particle interaction

First observation of rising-tone magnetosonic waves

Magnetosonic (MS) waves are linearly polarized emissions confined near the magnetic equator with wave normal angle near 90\textdegree and frequency below the lower hybrid frequency. Such waves, also termed equatorial noise, were traditionally known to be \textquotedbllefttemporally continuous\textquotedblright in their time-frequency spectrogram. Here we show for the first time that MS waves actually have discrete wave elements with rising-tone features in their spectrogram. The frequency sweep rate of MS waves, ~1 Hz/s, is between that of chorus and electromagnetic ion cyclotron (EMIC) waves. For the two events we analyzed, MS waves occur outside the plasmapause and cannot penetrate into the plasmasphere; their power is smaller than that of chorus. We suggest that the rising-tone feature of MS waves is a consequence of nonlinear wave-particle interaction, as is the case with chorus and EMIC waves.

Fu, H.; Cao, J.; Zhima, Z.; Khotyaintsev, Y.; Angelopoulos, V.; ik, O.; Omura, Y.; Taubenschuss, U.; Chen, L.; Huang, S;

Published by: Geophysical Research Letters      Published on: 11/2014

YEAR: 2014     DOI: 10.1002/grl.v41.2110.1002/2014GL061867

discrete; frequency sweep rate; magnetosonic wave; nonlinear wave-particle interaction; Plasmapause; rising tone

First observation of rising-tone magnetosonic waves

Magnetosonic (MS) waves are linearly polarized emissions confined near the magnetic equator with wave normal angle near 90\textdegree and frequency below the lower hybrid frequency. Such waves, also termed equatorial noise, were traditionally known to be \textquotedbllefttemporally continuous\textquotedblright in their time-frequency spectrogram. Here we show for the first time that MS waves actually have discrete wave elements with rising-tone features in their spectrogram. The frequency sweep rate of MS waves, ~1 Hz/s, is between that of chorus and electromagnetic ion cyclotron (EMIC) waves. For the two events we analyzed, MS waves occur outside the plasmapause and cannot penetrate into the plasmasphere; their power is smaller than that of chorus. We suggest that the rising-tone feature of MS waves is a consequence of nonlinear wave-particle interaction, as is the case with chorus and EMIC waves.

Fu, H.; Cao, J.; Zhima, Z.; Khotyaintsev, Y.; Angelopoulos, V.; ik, O.; Omura, Y.; Taubenschuss, U.; Chen, L.; Huang, S;

Published by: Geophysical Research Letters      Published on: 11/2014

YEAR: 2014     DOI: 10.1002/grl.v41.2110.1002/2014GL061867

discrete; frequency sweep rate; magnetosonic wave; nonlinear wave-particle interaction; Plasmapause; rising tone

An unusual long-lived relativistic electron enhancement event excited by sequential CMEs

An unusual long-lived intense relativistic electron enhancement event from July to August 2004 is examined using data from Fengyun-1, POES, GOES, ACE, the Cluster Mission and geomagnetic indices. During the initial 6 days of this event, the observed fluxes in the outer zone enhanced continuously and their maximum increased from 2.1 \texttimes 102 cm-2\textperiodcenteredsr-1\textperiodcentereds-1 to 3.5 \texttimes 104 cm-2\textperiodcenteredsr-1\textperiodcentereds-1, the region of enhanced fluxes extended from L = 3.5-6.5 to L = 2.5-6.5, and the flux peak location shifted inward from L ~ 4.2 to L ~ 3.3. During the following 7 days, without any locational movement, the flux peak increased slowly and exceeded the pre-storm fluxes by about 4 orders of magnitude. Subsequently, the decay rate of relativistic electrons is so slow that the peak remains over 104 cm-2\textperiodcenteredsr-1\textperiodcentereds-1 for about 30 days. The drift-resonance between ULF waves, which arose from high-speed solar wind and frequent impulses of solar wind dynamic pressure, and energetic electrons injected by substorms could be an important acceleration mechanism in this event. The local acceleration by whistler mode chorus could be another mechanism contributing to this enhancement. The plasmaspheric response to the interplanetary disturbances reveals that the enhanced outer zone is divided into two portions by the plasmapause. Accordingly, the slow loss rate in the plasmasphere due to hiss primarily contributed to the long-lived characteristic of this event. This event reveals that the outer zone population behaviors are dominated by the interplanetary variations together with the responses of geomagnetic field and plasmasphere to these variations.

Yang, Xiao; Zhu, Guang; Zhang, Xiao; Sun, Yue; Liang, Jin; Wei, Xin;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2014

YEAR: 2014     DOI: 10.1002/2014JA019797

Geomagnetic storm/substorm; Interplanetary magnetic field; Plasmapause; Relativistic electron; Solar wind

Modeling Gradual Diffusion Changes in Radiation Belt Electron Phase Space Density for the March 2013 Van Allen Probes Case Study

March 2013 provided the first equinoctial period when all of the instruments on the Van Allen Probes spacecraft were fully operational. This interval was characterized by disturbances of outer zone electrons with two timescales of variation, diffusive and rapid dropout and restoration [Baker et al., 2014]. A radial diffusion model was applied to the month-long interval to confirm that electron phase space density is well described by radial diffusion for the whole month at low first invariant <=400 MeV/G, but peaks in phase space density observed by the ECT instrument suite at higher first invariant are not reproduced by radial transport from a source at higher L. The model does well for much of the month-long interval, capturing three of four enhancements in phase space density which emerge from the outer boundary, while the strong enhancement following dropout on 17-18 March requires local acceleration at higher first invariant (M = 1000 MeV/G vs. 200 MeV/G) not included in our model. We have incorporated phase space density from ECT measurement at the outer boundary and plasmapause determination from the EFW instrument to separate hiss and chorus loss models.

Li, Zhao; Hudson, Mary; Jaynes, Allison; Boyd, Alexander; Malaspina, David; Thaller, Scott; Wygant, John; Henderson, Michael;

Published by: Journal of Geophysical Research: Space Physics      Published on: 10/2014

YEAR: 2014     DOI: 10.1002/2014JA020359

March 2013; radial diffusion; Van Allen Probes

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

Chorus-driven acceleration of radiation belt electrons in the unusual temporal/spatial regions

Cyclotron resonance with whistler-mode chorus waves is an important mechanism for the local acceleration of radiation belt energetic electrons. Such acceleration process has been widely investigated during the storm times, and its favored region is usually considered to be the low-density plasmatrough with magnetic local time (MLT) from midnight through dawn to noon. Here we present two case studies on the chorus-driven acceleration of radiation belt electrons in some \textquotedblleftunusual\textquotedblright temporal /spatial regions. (1) The first event recorded by the Van Allen Probes during the nonstorm times from 21 to 23 February 2013. Within two days, a new radiation belt centering around L=5.8 formed and gradually merged with the original outer belt. The corresponding relativistic electron fluxes increased by a factor of up to 50, accompanied by strong chorus waves. The quasi-linear STEERB model, including the local acceleration of detected chorus waves, can basically reproduce the observed 0.2\textendash5.0 MeV electron flux enhancement at the center of new belt. These results clearly illustrate the importance of chorus-driven local acceleration during the nonstorm times. (2) The second event observed by the Van Allen Probes in the duskside (MLT\~18) region on 2 October 2013. The quasi-linear diffusion analysis of STEERB code shows that, even in the duskside region with large ratio between the electron plasma frequency and the electron gyrofrequency, the detected intense (\~0.5 nT) chorus waves can still effectively accelerate radiation belt electrons. These results clearly exhibit the broader effective acceleration regions than usually estimated, at least for this one example.

Su, Zhenpeng; Xiao, Fuliang; Zheng, Huinan; Zhu, Hui;

Published by:       Published on: 08/2014

YEAR: 2014     DOI: 10.1109/URSIGASS.2014.6929875

Acceleration; Van Allen Belts; Van Allen Probes

Observations of the inner radiation belt: CRAND and trapped solar protons

Measurements of inner radiation belt protons have been made by the Van Allen Probes Relativistic Electron-Proton Telescopes as a function of kinetic energy (24 to 76 MeV), equatorial pitch angle, and magnetic L shell, during late-2013 and early-2014. A probabilistic data analysis method reduces background from contamination by higher energy protons. Resulting proton intensities are compared to predictions of a theoretical radiation belt model. Then trapped protons originating both from cosmic ray albedo neutron decay (CRAND) and from trapping of solar protons are evident in the measured distributions. An observed double-peaked distribution in L is attributed, based on the model comparison, to a gap in the occurrence of solar proton events during the 2007 to 2011 solar minimum. Equatorial pitch angle distributions show that trapped solar protons are confined near the magnetic equator, but that CRAND protons can reach low-altitudes. Narrow pitch angle distributions near the outer edge of the inner belt are characteristic of proton trapping limits.

Selesnick, R.; Baker, D.; Jaynes, A.; Li, X.; Kanekal, S.; Hudson, M.; Kress, B.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 08/2014

YEAR: 2014     DOI: 10.1002/2014JA020188

Van Allen Probes

Boom and bust for radiation belt high-energy electron populations

Launched on 30 August 2012, the twin Van Allen probes constitute the first dedicated mission in decades to study the Earth\textquoterights radiation belts. The sensor-laden spacecraft follow a nearly equatorial orbit, which gives them a complete view of the full range of radiation belt processes. In a new study, Baker et al. lay out some of the surprising results unveiled by the crafts\textquoteright first year in orbit.

Schultz, Colin;

Published by: Eos, Transactions American Geophysical Union      Published on: 07/2014

YEAR: 2014     DOI: 10.1002/eost.v95.2810.1002/2014EO280021

Van Allen Probes

The Energetic Particle Detector (EPD) Investigation and the Energetic Ion Spectrometer (EIS) for the Magnetospheric Multiscale (MMS) Mission

The Energetic Particle Detector (EPD) Investigation is one of 5 fields-and-particles investigations on the Magnetospheric Multiscale (MMS) mission. MMS comprises 4 spacecraft flying in close formation in highly elliptical, near-Earth-equatorial orbits targeting understanding of the fundamental physics of the important physical process called magnetic reconnection using Earth\textquoterights magnetosphere as a plasma laboratory. EPD comprises two sensor types, the Energetic Ion Spectrometer (EIS) with one instrument on each of the 4 spacecraft, and the Fly\textquoterights Eye Energetic Particle Spectrometer (FEEPS) with 2 instruments on each of the 4 spacecraft. EIS measures energetic ion energy, angle and elemental compositional distributions from a required low energy limit of 20 keV for protons and 45 keV for oxygen ions, up to >0.5 MeV (with capabilities to measure up to >1 MeV). FEEPS measures instantaneous all sky images of energetic electrons from 25 keV to >0.5 MeV, and also measures total ion energy distributions from 45 keV to >0.5 MeV to be used in conjunction with EIS to measure all sky ion distributions. In this report we describe the EPD investigation and the details of the EIS sensor. Specifically we describe EPD-level science objectives, the science and measurement requirements, and the challenges that the EPD team had in meeting these requirements. Here we also describe the design and operation of the EIS instruments, their calibrated performances, and the EIS in-flight and ground operations. Blake et al. (The Flys Eye Energetic Particle Spectrometer (FEEPS) contribution to the Energetic Particle Detector (EPD) investigation of the Magnetospheric Magnetoscale (MMS) Mission, this issue) describe the design and operation of the FEEPS instruments, their calibrated performances, and the FEEPS in-flight and ground operations. The MMS spacecraft will launch in early 2015, and over its 2-year mission will provide comprehensive measurements of magnetic reconnection at Earth\textquoterights magnetopause during the 18 months that comprise orbital phase 1, and magnetic reconnection within Earth\textquoterights magnetotail during the about 6 months that comprise orbital phase 2.

Mauk, B.; Blake, J.; Baker, D.; Clemmons, J.; Reeves, G.; Spence, H.; Jaskulek, S.; Schlemm, C.; Brown, L.; Cooper, S.; Craft, J.; Fennell, J.; Gurnee, R.; Hammock, C.; Hayes, J.; Hill, P.; Ho, G.; Hutcheson, J.; Jacques, A.; Kerem, S.; Mitchell, D.; Nelson, K.; Paschalidis, N.; Rossano, E.; Stokes, M.; Westlake, J.;

Published by: Space Science Reviews      Published on: 06/2014

YEAR: 2014     DOI: 10.1007/s11214-014-0055-5

Magnetic reconnection; Magnetosphere; Magnetospheric multiscale; NASA mission; Particle acceleration; Space plasma

Intense duskside lower band chorus waves observed by Van Allen Probes: Generation and potential acceleration effect on radiation belt electrons

Local acceleration driven by whistler mode chorus waves largely accounts for the enhancement of radiation belt relativistic electron fluxes, whose favored region is usually considered to be the plasmatrough with magnetic local time approximately from midnight through dawn to noon. On 2 October 2013, the Van Allen Probes recorded a rarely reported event of intense duskside lower band chorus waves (with power spectral density up to 10-3nT2/Hz) in the low-latitude region outside of L=5. Such chorus waves are found to be generated by the substorm-injected anisotropic suprathermal electrons and have a potentially strong acceleration effect on the radiation belt energetic electrons. This event study demonstrates the possibility of broader spatial regions with effective electron acceleration by chorus waves than previously expected. For such intense duskside chorus waves, the occurrence probability, the preferential excitation conditions, the time duration, and the accurate contribution to the long-term evolution of radiation belt electron fluxes may need further investigations in future.

Su, Zhenpeng; Zhu, Hui; Xiao, Fuliang; Zheng, Huinan; Wang, Yuming; He, Zhaoguo; Shen, Chao; Shen, Chenglong; Wang, C.; Liu, Rui; Zhang, Min; Wang, Shui; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.; Wygant, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 06/2014

YEAR: 2014     DOI: 10.1002/jgra.v119.610.1002/2014JA019919

Van Allen Probes

On the cause and extent of outer radiation belt losses during the 30 September 2012 dropout event

On 30 September 2012, a flux \textquotedblleftdropout\textquotedblright occurred throughout Earth\textquoterights outer electron radiation belt during the main phase of a strong geomagnetic storm. Using eight spacecraft from NASA\textquoterights Time History of Events and Macroscale Interactions during Substorms (THEMIS) and Van Allen Probes missions and NOAA\textquoterights Geostationary Operational Environmental Satellites constellation, we examined the full extent and timescales of the dropout based on particle energy, equatorial pitch angle, radial distance, and species. We calculated phase space densities of relativistic electrons, in adiabatic invariant coordinates, which revealed that loss processes during the dropout were > 90\% effective throughout the majority of the outer belt and the plasmapause played a key role in limiting the spatial extent of the dropout. THEMIS and the Van Allen Probes observed telltale signatures of loss due to magnetopause shadowing and subsequent outward radial transport, including similar loss of energetic ring current ions. However, Van Allen Probes observations suggest that another loss process played a role for multi-MeV electrons at lower L shells (L* < ~4).

Turner, D.; Angelopoulos, V.; Morley, S.; Henderson, M.; Reeves, G.; Li, W.; Baker, D.; Huang, C.-L.; Boyd, A.; Spence, H.; Claudepierre, S.; Blake, J.; Rodriguez, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2014

YEAR: 2014     DOI: 10.1002/2013JA019446

dropouts; inner magnetosphere; loss; Radiation belts; relativistic electrons; Van Allen Probes

Competing source and loss mechanisms due to wave-particle interactions in Earth\textquoterights outer radiation belt during the 30 September to 3 October 2012 geomagnetic storm

Drastic variations of Earth\textquoterights outer radiation belt electrons ultimately result from various competing source, loss, and transport processes, to which wave-particle interactions are critically important. Using 15 spacecraft including NASA\textquoterights Van Allen Probes, THEMIS, and SAMPEX missions and NOAA\textquoterights GOES and POES constellations, we investigated the evolution of the outer belt during the strong geomagnetic storm of 30 September to 3 October 2012. This storm\textquoterights main phase dropout exhibited enhanced losses to the atmosphere at L* < 4, where the phase space density (PSD) of multi-MeV electrons dropped by over an order of magnitude in <4 h. Based on POES observations of precipitating >1 MeV electrons and energetic protons, SAMPEX >1 MeV electrons, and ground observations of band-limited Pc1-2 wave activity, we show that this sudden loss was consistent with pitch angle scattering by electromagnetic ion cyclotron waves in the dusk magnetic local time sector at 3 < L* < 4. At 4 < L* < 5, local acceleration was also active during the main and early recovery phases, when growing peaks in electron PSD were observed by both Van Allen Probes and THEMIS. This acceleration corresponded to the period when IMF Bz was southward, the AE index was >300 nT, and energetic electron injections and whistler-mode chorus waves were observed throughout the inner magnetosphere for >12 h. After this period, Bz turned northward, and injections, chorus activity, and enhancements in PSD ceased. Overall, the outer belt was depleted by this storm. From the unprecedented level of observations available, we show direct evidence of the competitive nature of different wave-particle interactions controlling relativistic electron fluxes in the outer radiation belt.

Turner, D.; Angelopoulos, V.; Li, W.; Bortnik, J.; Ni, B.; Ma, Q.; Thorne, R.; Morley, S.; Henderson, M.; Reeves, G.; Usanova, M.; Mann, I.; Claudepierre, S.; Blake, J.; Baker, D.; Huang, C.-L.; Spence, H.; Kurth, W.; Kletzing, C.; Rodriguez, J.;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2014

YEAR: 2014     DOI: 10.1002/jgra.v119.310.1002/2014JA019770

Van Allen Probes

Gradual diffusion and punctuated phase space density enhancements of highly relativistic electrons: Van Allen Probes observations

The dual-spacecraft Van Allen Probes mission has provided a new window into mega electron volt (MeV) particle dynamics in the Earth\textquoterights radiation belts. Observations (up to E ~10 MeV) show clearly the behavior of the outer electron radiation belt at different timescales: months-long periods of gradual inward radial diffusive transport and weak loss being punctuated by dramatic flux changes driven by strong solar wind transient events. We present analysis of multi-MeV electron flux and phase space density (PSD) changes during March 2013 in the context of the first year of Van Allen Probes operation. This March period demonstrates the classic signatures both of inward radial diffusive energization and abrupt localized acceleration deep within the outer Van Allen zone (L ~4.0 \textpm 0.5). This reveals graphically that both \textquotedblleftcompeting\textquotedblright mechanisms of multi-MeV electron energization are at play in the radiation belts, often acting almost concurrently or at least in rapid succession.

Baker, D.; Jaynes, A.; Li, X.; Henderson, M.; Kanekal, S.; Reeves, G.; Spence, H.; Claudepierre, S.; Fennell, J.; Hudson, M.; Thorne, R.; Foster, J.; Erickson, P.; Malaspina, D.; Wygant, J.; Boyd, A.; Kletzing, C.; Drozdov, A.; Shprits, Y;

Published by: Geophysical Research Letters      Published on: 03/2014

YEAR: 2014     DOI: 10.1002/2013GL058942

Van Allen Probes

Radial diffusion comparing a THEMIS statistical model with geosynchronous measurements as input

The outer boundary energetic electron flux is used as a driver in radial diffusion calculations, and its precise determination is critical to the solution. A new model was proposed recently based on Time History of Events and Macroscale Interactions during Substorms (THEMIS) measurements to express the boundary flux as three fit functions of solar wind parameters in a response window that depend on energy and which solar wind parameter is used: speed, density, or both. The Dartmouth radial diffusion model has been run using Los Alamos National Laboratory (LANL) geosynchronous satellite measurements as the constraint for a one-month interval in July to August 2004, and the calculated phase space density (PSD) is compared with GPS measurements, at magnetic equatorial plane crossings, as a test of the model. We also used the PSD generated from the Shin and Lee model as constraint and examined it by computing the error relative to the LANL geosynchronous spacecraft data-driven run. The calculation shows that there is overestimation and underestimation at different times; however, the direct insertion of the statistical model can be used to drive the radial diffusion model generally, producing the phase space density dropout and increase during a storm. Having this model based on a solar wind parameterized data set, we can run the radial diffusion model for storms when particle measurements are not available as input. We chose the Whole Heliosphere Interval as an example and compared the result with MHD/test-particle simulations, obtaining better agreement with GPS measurement using the diffusion model, which incorporates atmospheric losses and an initial equilibrium radial profile.

Li, Zhao; Hudson, Mary; Chen, Yue;

Published by: Journal of Geophysical Research: Space Physics      Published on: 03/2014

YEAR: 2014     DOI: 10.1002/jgra.v119.310.1002/2013JA019320

outer boundary; radial diffusion; Radiation belt; Van Allen Probes

Rebuilding of the Earth\textquoterights outer electron belt during 8-10 October 2012

Geomagnetic storms often include strong magnetospheric convection caused by sustained periods of southward interplanetary magnetic field. During periods of strong convection, the Alfv\ en layer, which separates the region of sunward convection from closed drift shells, is displaced earthward allowing plasma sheet particles with energies in the hundreds of keV direct access inside of geosynchronous. Subsequent outward motion of the Alfv\ en boundary and adiabatic energization during storm recovery traps plasma sheet electrons on closed drift shells providing a seed population for the outer radiation belts. In situ observations of the 8\textendash10 October 2012 geomagnetic storm and MHD test particle simulations illustrate the morphology of this process. Data and modeling results support the conclusion that recovery of ~ 1 MeV electrons at geosynchronous is mainly due to global convection and dipolarization associated injections from the plasma sheet.

Kress, B.; Hudson, M.; Paral, J.;

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

YEAR: 2014     DOI: 10.1002/2013GL058588

radiation belt transport

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

Nonstorm time dynamics of electron radiation belts observed by the Van Allen Probes

Storm time electron radiation belt dynamics have been widely investigated for many years. Here we present a rarely reported nonstorm time event of electron radiation belt evolution observed by the Van Allen Probes during 21\textendash24 February 2013. Within 2 days, a new belt centering around L=5.8 formed and gradually merged with the original outer belt, with the enhancement of relativistic electron fluxes by a factor of up to 50. Strong chorus waves (with power spectral density up to 10-4nT2/Hz) occurred in the region L>5. Taking into account the local acceleration driven by these chorus waves, the two-dimensional STEERB can approximately reproduce the observed energy spectrums at the center of the new belt. These results clearly illustrate the complexity of electron radiation belt behaviors and the importance of chorus-driven local acceleration even during the nonstorm times.

Su, Zhenpeng; Xiao, Fuliang; Zheng, Huinan; He, Zhaoguo; Zhu, Hui; Zhang, Min; Shen, Chao; Wang, Yuming; Wang, Shui; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Funsten, H.; Blake, J.; Baker, D.;

Published by: Geophysical Research Letters      Published on: 01/2014

YEAR: 2014     DOI: 10.1002/2013GL058912

Van Allen Probes

Dynamics of the Earth\textquoterights Radiation Belts and Inner Magnetosphere

Trapped by Earth\textquoterights magnetic field far above the planet\textquoterights surface, the energetic particles that fill the radiation belts are a sign of the Sun\textquoterights influence and a threat to our technological future. In the AGU monograph Dynamics of the Earth\textquoterights Radiation Belts and Inner Magnetosphere, editors Danny Summers, Ian R. Mann, Daniel N. Baker, and Michael Schulz explore the inner workings of the magnetosphere. The book reviews current knowledge of the magnetosphere and recent research results and sets the stage for the work currently being done by NASA\textquoterights Van Allen Probes (formerly known as the Radiation Belt Storm Probes). In this interview, Eos talks to Summers about magnetospheric research, whistler mode waves, solar storms, and the effects of the radiation belts on Earth.

Schultz, Colin;

Published by: Eos, Transactions American Geophysical Union      Published on: 12/2013

YEAR: 2013     DOI: 10.1002/eost.v94.5210.1002/2013EO520007

aurora; Magnetosphere; Radiation belts; Van Allen Probes

Space physics: A fast lane in the magnetosphere

A marriage between satellite observations and modelling has shown that acceleration of electrons in the magnetosphere can be explained by scattering of these particles by plasma oscillations known as chorus waves.

Hudson, M.;

Published by: Nature      Published on: 12/2013

YEAR: 2013     DOI: 10.1038/504383a

Van Allen Probes

AE9, AP9 and SPM: New Models for Specifying the Trapped Energetic Particle and Space Plasma Environment

The radiation belts and plasma in the Earth\textquoterights magnetosphere pose hazards to satellite systems which restrict design and orbit options with a resultant impact on mission performance and cost. For decades the standard space environment specification used for spacecraft design has been provided by the NASA AE8 and AP8 trapped radiation belt models. There are well-known limitations on their performance, however, and the need for a new trapped radiation and plasma model has been recognized by the engineering community for some time. To address this challenge a new set of models, denoted AE9/AP9/SPM, for energetic electrons, energetic protons and space plasma has been developed. The new models offer significant improvements including more detailed spatial resolution and the quantification of uncertainty due to both space weather and instrument errors. Fundamental to the model design, construction and operation are a number of new data sets and a novel statistical approach which captures first order temporal and spatial correlations allowing for the Monte-Carlo estimation of flux thresholds for user-specified percentile levels (e.g., 50th and 95th) over the course of the mission. An overview of the model architecture, data reduction methods, statistics algorithms, user application and initial validation is presented in this paper.

Ginet, G.; textquoterightBrien, T.; Huston, S.; Johnston, W.; Guild, T.; Friedel, R.; Lindstrom, C.; Roth, C.; Whelan, P.; Quinn, R.; Madden, D.; Morley, S.; Su, Yi-Jiun;

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

YEAR: 2013     DOI: 10.1007/s11214-013-9964-y

RBSP; Van Allen Probes

The Balloon Array for RBSP Relativistic Electron Losses (BARREL)

BARREL is a multiple-balloon investigation designed to study electron losses from Earth\textquoterights Radiation Belts. Selected as a NASA Living with a Star Mission of Opportunity, BARREL augments the Radiation Belt Storm Probes mission by providing measurements of relativistic electron precipitation with a pair of Antarctic balloon campaigns that will be conducted during the Austral summers (January-February) of 2013 and 2014. During each campaign, a total of 20 small (\~20 kg) stratospheric balloons will be successively launched to maintain an array of \~5 payloads spread across \~6 hours of magnetic local time in the region that magnetically maps to the radiation belts. Each balloon carries an X-ray spectrometer to measure the bremsstrahlung X-rays produced by precipitating relativistic electrons as they collide with neutrals in the atmosphere, and a DC magnetometer to measure ULF-timescale variations of the magnetic field. BARREL will provide the first balloon measurements of relativistic electron precipitation while comprehensive in situ measurements of both plasma waves and energetic particles are available, and will characterize the spatial scale of precipitation at relativistic energies. All data and analysis software will be made freely available to the scientific community.

Millan, R.; McCarthy, M.; Sample, J.; Smith, D.; Thompson, L.; McGaw, D.; Woodger, L.; Hewitt, J.; Comess, M.; Yando, K.; Liang, A.; Anderson, B.; Knezek, N.; Rexroad, W.; Scheiman, J.; Bowers, G.; Halford, A.; Collier, A.; Clilverd, M.; Lin, R.; Hudson, M.;

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

YEAR: 2013     DOI: 10.1007/s11214-013-9971-z

RBSP; Van Allen Probes

The Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) on RBSP

The Electric and Magnetic Field Instrument and Integrated Science (EMFISIS) investigation on the NASA Radiation Belt Storm Probes (now named the Van Allen Probes) mission provides key wave and very low frequency magnetic field measurements to understand radiation belt acceleration, loss, and transport. The key science objectives and the contribution that EMFISIS makes to providing measurements as well as theory and modeling are described. The key components of the instruments suite, both electronics and sensors, including key functional parameters, calibration, and performance, demonstrate that EMFISIS provides the needed measurements for the science of the RBSP mission. The EMFISIS operational modes and data products, along with online availability and data tools provide the radiation belt science community with one the most complete sets of data ever collected.

Kletzing, C.; Kurth, W.; Acuna, M.; MacDowall, R.; Torbert, R.; Averkamp, T.; Bodet, D.; Bounds, S.; Chutter, M.; Connerney, J.; Crawford, D.; Dolan, J.; Dvorsky, R.; Hospodarsky, G.; Howard, J.; Jordanova, V.; Johnson, R.; Kirchner, D.; Mokrzycki, B.; Needell, G.; Odom, J.; Mark, D.; Pfaff, R.; Phillips, J.; Piker, C.; Remington, S.; Rowland, D.; Santolik, O.; Schnurr, R.; Sheppard, D.; Smith, C.; Thorne, R.; Tyler, J.;

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

YEAR: 2013     DOI: 10.1007/s11214-013-9993-6

RBSP; 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

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 Storm Probes Ion Composition Experiment (RBSPICE)

The Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) on the two Van Allen Probes spacecraft is the magnetosphere ring current instrument that will provide data for answering the three over-arching questions for the Van Allen Probes Program: RBSPICE will determine \textquotedbllefthow space weather creates the storm-time ring current around Earth, how that ring current supplies and supports the creation of the radiation belt populations,\textquotedblright and how the ring current is involved in radiation belt losses. RBSPICE is a time-of-flight versus total energy instrument that measures ions over the energy range from \~20 keV to \~1 MeV. RBSPICE will also measure electrons over the energy range \~25 keV to \~1 MeV in order to provide instrument background information in the radiation belts. A description of the instrument and its data products are provided in this chapter.

Mitchell, D.; Lanzerotti, L.; Kim, C.; Stokes, M.; Ho, G.; Cooper, S.; UKHORSKIY, A; Manweiler, J.; Jaskulek, S.; Haggerty, D.; Brandt, P.; SITNOV, M; Keika, K.; Hayes, J.; Brown, L.; Gurnee, R.; Hutcheson, J.; Nelson, K.; Paschalidis, N.; Rossano, E.; Kerem, S.;

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

YEAR: 2013     DOI: 10.1007/s11214-013-9965-x

RBSP; Van Allen Probes

The Relativistic Electron-Proton Telescope (REPT) Instrument on Board the Radiation Belt Storm Probes (RBSP) Spacecraft: Characterization of Earth\textquoterights Radiation Belt High-Energy Particle Populations

Particle acceleration and loss in the million electron Volt (MeV) energy range (and above) is the least understood aspect of radiation belt science. In order to measure cleanly and separately both the energetic electron and energetic proton components, there is a need for a carefully designed detector system. The Relativistic Electron-Proton Telescope (REPT) on board the Radiation Belt Storm Probe (RBSP) pair of spacecraft consists of a stack of high-performance silicon solid-state detectors in a telescope configuration, a collimation aperture, and a thick case surrounding the detector stack to shield the sensors from penetrating radiation and bremsstrahlung. The instrument points perpendicular to the spin axis of the spacecraft and measures high-energy electrons (up to \~20 MeV) with excellent sensitivity and also measures magnetospheric and solar protons to energies well above E=100 MeV. The instrument has a large geometric factor (g=0.2 cm2 sr) to get reasonable count rates (above background) at the higher energies and yet will not saturate at the lower energy ranges. There must be fast enough electronics to avert undue dead-time limitations and chance coincidence effects. The key goal for the REPT design is to measure the directional electron intensities (in the range 10-2\textendash106 particles/cm2 s sr MeV) and energy spectra (ΔE/E\~25 \%) throughout the slot and outer radiation belt region. Present simulations and detailed laboratory calibrations show that an excellent design has been attained for the RBSP needs. We describe the engineering design, operational approaches, science objectives, and planned data products for REPT.

Baker, D.; Kanekal, S.; Hoxie, V.; Batiste, S.; Bolton, M.; Li, X.; Elkington, S.; Monk, S.; Reukauf, R.; Steg, S.; Westfall, J.; Belting, C.; Bolton, B.; Braun, D.; Cervelli, B.; Hubbell, K.; Kien, M.; Knappmiller, S.; Wade, S.; Lamprecht, B.; Stevens, K.; Wallace, J.; Yehle, A.; Spence, H.; Friedel, R.;

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

YEAR: 2013     DOI: 10.1007/s11214-012-9950-9

RBSP; Van Allen Probes

Science Goals and Overview of the Energetic Particle, Composition, and Thermal Plasma (ECT) Suite on NASA\textquoterights Radiation Belt Storm Probes (RBSP) Mission

The Radiation Belt Storm Probes (RBSP)-Energetic Particle, Composition, and Thermal Plasma (ECT) suite contains an innovative complement of particle instruments to ensure the highest quality measurements ever made in the inner magnetosphere and radiation belts. The coordinated RBSP-ECT particle measurements, analyzed in combination with fields and waves observations and state-of-the-art theory and modeling, are necessary for understanding the acceleration, global distribution, and variability of radiation belt electrons and ions, key science objectives of NASA\textquoterights Living With a Star program and the Van Allen Probes mission. The RBSP-ECT suite consists of three highly-coordinated instruments: the Magnetic Electron Ion Spectrometer (MagEIS), the Helium Oxygen Proton Electron (HOPE) sensor, and the Relativistic Electron Proton Telescope (REPT). Collectively they cover, continuously, the full electron and ion spectra from one eV to 10\textquoterights of MeV with sufficient energy resolution, pitch angle coverage and resolution, and with composition measurements in the critical energy range up to 50 keV and also from a few to 50 MeV/nucleon. All three instruments are based on measurement techniques proven in the radiation belts. The instruments use those proven techniques along with innovative new designs, optimized for operation in the most extreme conditions in order to provide unambiguous separation of ions and electrons and clean energy responses even in the presence of extreme penetrating background environments. The design, fabrication and operation of ECT spaceflight instrumentation in the harsh radiation belt environment ensure that particle measurements have the fidelity needed for closure in answering key mission science questions. ECT instrument details are provided in companion papers in this same issue. In this paper, we describe the science objectives of the RBSP-ECT instrument suite on the Van Allen Probe spacecraft within the context of the overall mission objectives, indicate how the characteristics of the instruments satisfy the requirements to achieve these objectives, provide information about science data collection and dissemination, and conclude with a description of some early mission results.

Spence, H.; Reeves, G.; Baker, D.; Blake, J.; Bolton, M.; Bourdarie, S.; Chan, A.; Claudpierre, S.; Clemmons, J.; Cravens, J.; Elkington, S.; Fennell, J.; Friedel, R.; Funsten, H.; Goldstein, J.; Green, J.; Guthrie, A.; Henderson, M.; Horne, R.; Hudson, M.; Jahn, J.-M.; Jordanova, V.; Kanekal, S.; Klatt, B.; Larsen, B.; Li, X.; MacDonald, E.; Mann, I.R.; Niehof, J.; O\textquoterightBrien, T.; Onsager, T.; Salvaggio, D.; Skoug, R.; Smith, S.; Suther, L.; Thomsen, M.; Thorne, R.;

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

YEAR: 2013     DOI: DOI: 10.1007/s11214-013-0007-5

RBSP; Van Allen Probes

Van Allen Probes observation of localized drift-resonance between poloidal mode ultra-low frequency waves and 60 keV electrons

[1] We present NASA Van Allen Probes observations of wave-particle interactions between magnetospheric ultra-low frequency (ULF) waves and energetic electrons (20\textendash500 keV) on 31 October 2012. The ULF waves are identified as the fundamental poloidal mode oscillation and are excited following an interplanetary shock impact on the magnetosphere. Large amplitude modulations in energetic electron flux are observed at the same period (≈ 3 min) as the ULF waves and are consistent with a drift-resonant interaction. The azimuthal mode number of the interacting wave is estimated from the electron measurements to be ~40, based on an assumed symmetric drift resonance. The drift-resonant interaction is observed to be localized and occur over 5\textendash6 wave cycles, demonstrating peak electron flux modulations at energies ~60 keV. Our observation clearly shows electron drift resonance with the fundamental poloidal mode, the energy dependence of the amplitude and phase of the electron flux modulations providing strong evidence for such an interaction. Significantly, the observation highlights the importance of localized wave-particle interactions for understanding energetic particle dynamics in the inner magnetosphere, through the intermediary of ULF waves.

Claudepierre, S.; Mann, I.R.; Takahashi, K; Fennell, J.; Hudson, M.; Blake, J.; Roeder, J.; Clemmons, J.; Spence, H.; Reeves, G.; Baker, D.; Funsten, H.; Friedel, R.; Henderson, M.; Kletzing, C.; Kurth, W.; Wygant, J.;

Published by: Geophysical Research Letters      Published on: 09/2013

YEAR: 2013     DOI: 10.1002/grl.50901

RBSP; Van Allen Probes

A Long-Lived Relativistic Electron Storage Ring Embedded in Earth\textquoterights Outer Van Allen Belt

Since their discovery more than 50 years ago, Earth\textquoterights Van Allen radiation belts have been considered to consist of two distinct zones of trapped, highly energetic charged particles. The outer zone is composed predominantly of megaelectron volt (MeV) electrons that wax and wane in intensity on time scales ranging from hours to days, depending primarily on external forcing by the solar wind. The spatially separated inner zone is composed of commingled high-energy electrons and very energetic positive ions (mostly protons), the latter being stable in intensity levels over years to decades. In situ energy-specific and temporally resolved spacecraft observations reveal an isolated third ring, or torus, of high-energy (>2 MeV) electrons that formed on 2 September 2012 and persisted largely unchanged in the geocentric radial range of 3.0 to ~3.5 Earth radii for more than 4 weeks before being disrupted (and virtually annihilated) by a powerful interplanetary shock wave passage.

Baker, D.; Kanekal, S.; Hoxie, V.; Henderson, M.; Li, X.; Spence, H.; Elkington, S.; Friedel, R.; Goldstein, J.; Hudson, M.; Reeves, G.; Thorne, R.; Kletzing, C.; Claudepierre, S.;

Published by: Science      Published on: 04/2013

YEAR: 2013     DOI: 10.1126/science.1233518

RBSP; Van Allen Probes

Energetic radiation belt electron precipitation showing ULF modulation

1] The energization and loss processes for energetic radiation belt electrons are not yet well understood. Ultra Low Frequency (ULF) waves have been correlated with both enhancement in outer zone radiation belt electron flux and modulation of precipitation loss to the atmosphere. This study considers the effects of ULF waves in the Pc-4 to Pc-5 period range (45 s\textendash600 s) on electron loss to the atmosphere on a time scale of several minutes. Global simulations using magnetohydrodynamics (MHD) model fields as drivers provide a valuable tool for studying the dynamics of these \~MeV energetic particles. ACE satellite measurements of the MHD solar wind parameters are used as the upstream boundary condition for the Lyon-Fedder-Mobarry (LFM) 3D MHD code calculation of fields, used to drive electrons in a 3D test particle simulation that keeps track of attributes like energy, pitch-angle and L-shell. The simulation results are compared with balloon observations obtained during the January 21, 2005 CME-shock event. Rapid loss of 20 keV to 1.5 MeV electrons was detected by balloon-borne measurements ofbremsstrahlungX-rays during the MINIS campaign following the shock arrival at Earth. The global precipitation response of the radiation belts to this CME-shock driven storm was investigated focusing on their interaction with ULF waves. A primary cause for the precipitation modulation seen in both the simulation and the MINIS campaign is suggested based on the lowering of mirror points due to compressional magnetic field oscillations.

Brito, T.; Woodger, L.; Hudson, M.; MILLAN, R;

Published by: Geophysical Research Letters      Published on: 11/2012

YEAR: 2012     DOI: 10.1029/2012GL053790

Charged particle motion and acceleration; Energetic particles: precipitating; Radiation belts; wave-particle interactions

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

Global MHD test particle simulations of solar energetic electron trapping in the Earth\textquoterights radiation belts

Test-particle trajectories are computed in fields from a global MHD magnetospheric model simulation of the 29 October 2003 Storm Commencement to investigate trapping and transport of solar energetic electrons (SEEs) in the magnetosphere during severe storms. SEEs are found to provide a source population for a newly formed belt of View the MathML source electrons in the Earth\textquoterights inner zone radiation belts, which was observed following the 29 October 2003 storm. Energy and pitch angle distributions of the new belt are compared with results previously obtained [Kress, B.T., Hudson, M.K., Looper, M.D., Albert, J., Lyon, J.G., Goodrich, C.C., 2007. Global MHD test particle simulations of >10 MeV radiation belt electrons during storm sudden commencement. Journal of Geophysical Research 112, A09215, doi:10.1029/2006JA012218], where outer belt electrons were used as a source for the new belt.

KRESS, B; Hudson, M.; LOOPER, M; LYON, J; GOODRICH, C;

Published by: Journal of Atmospheric and Solar-Terrestrial Physics      Published on: 11/2008

YEAR: 2008     DOI: 10.1016/j.jastp.2008.05.018

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