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Found 29 entries in the Bibliography.
Showing entries from 1 through 29
| 2021 |
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Abstract The coupling response between solar wind structures and the magnetosphere is highly complex, leading to different effects in the outer radiation belt electron fluxes. Most Coronal Mass Ejections cause strong geomagnetic storms with short recovery phases, often 1-2 days. By contrast, High-Speed Solar Wind Streams lead to moderate and weak storms often with much longer recovery phases, from several to ∼10 days. The magnetosphere receives energy for a long time under the influence of the HSSs, considerably changing its dynamics. This in turn has an effect on the charged particles trapped in the outer radiation belt. Although the high-energy electron flux enhancements have received considerable attention, the high-energy electron flux enhancement pattern (L > 4) has not. This paper identifies 37 events with this enhancement pattern in the high-energy electron flux during the Van Allen Probes era. We find the enhancements coincident with HSS occurrence. The interplanetary magnetic field (IMF) exhibits north/south Bz fluctuations of Alfvénic nature with moderate amplitudes. The high-energy electron flux enhancements also correspond to long periods of auroral activity indicating a relationship to magnetotail dynamics. However, the AE index only reaches moderate values. Ultra-Low Frequency waves were present in all of the events and whistler-mode chorus waves were present in 89.1\% of the events, providing a convenient scenario for wave-particle interactions. The radial gradient of the ULF wave power related to the L, under the influence of the HSSs, is necessary to trigger the physical processes responsible for this type of high-energy electron flux enhancement pattern. This article is protected by copyright. All rights reserved. Da Silva, L.; Shi, J.; Alves, L.; Sibeck, D.; Marchezi, J.; Medeiros, C.; Vieira, L.; Agapitov, O.; Cardoso, F.; Souza, V.; Dal Lago, A.; Jauer, P.; Wang, C.; Li, H.; Liu, Z.; Alves, M.; Rockenbach, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2021 YEAR: 2021 DOI: https://doi.org/10.1029/2021JA029363 outer radiation belt; high-energy electron flux; high speed solar wind stream; ultra low frequency waves; whistler-mode chorus waves; Electron flux enhancement; Van Allen Probes |
| 2020 |
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We present a study analyzing relativistic and ultra relativistic electron energization and the evolution of pitch angle distributions using data from the Van Allen Probes. We study the connection between energization and isotropization to determine if there is a coherence across storms and across energies. Pitch angle distributions are fit with a J0sinnθ function, and the variable ’n’ is characterized as the pitch angle index and tracked over time. Our results show that, consistently across all storms with ultra relativistic electron energization, electron distributions are most anisotropic within around a day of Dstmin and become more isotropic in the following week. Also, each consecutively higher energy channel is associated with higher anisotropy after storm main phase. Changes in the pitch angle index are reflected in each energy channel; when 1.8 MeV electron pitch angle distributions increase (or decrease) in pitch angle index, so do the other energy channels. We show that the peak anisotropies differ between CME- and CIR- driven storms and measure the relaxation rate as the anisotropy falls after the storm. The isotropization rate in pitch angle index for CME-driven storms is -0.15±0.02 day−1 at 1.8 MeV, -0.30±0.01 day−1 at 3.4 MeV, and -0.39±0.02 day−1 at 5.2 MeV. For CIR-driven storms, the isotropization rates are -0.10±0.01 day−1 for 1.8 MeV, -0.13±0.02 day−1 for 3.4 MeV, and -0.11±0.02 day−1 for 5.2 MeV. This study shows that there is a global coherence across energies and that storm type may play a role in the evolution of electron pitch angle distributions. Greeley, Ashley; Kanekal, Shrikanth; Sibeck, David; Schiller, Quintin; Baker, Daniel; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028335 pitch angle distributions; relativistic electrons; ultra relativistic electrons; Van Allen Probes; pitch angle distribution evolution; anisotropic electrons |
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Multi-Parameter Chorus and Plasmaspheric Hiss Wave Models Abstract The resonant interaction of energetic particles with plasma waves, such as chorus and plasmaspheric hiss waves, plays a direct and crucial role in the acceleration and loss of radiation belt electrons that ultimately affect the dynamics of the radiation belts. In this study, we use the comprehensive wave data measurements made by the Electric and Magnetic Field Instrument Suite and Integrated Science instruments on board the two Van Allen probes, to develop multi-parameter statistical chorus and plasmaspheric hiss wave models. The models of chorus and plasmaspheric hiss waves are presented as a function of combined geomagnetic activity (AE), solar wind velocity (V), and southward interplanetary magnetic field (Bs). The relatively smooth wave models reveal new features. Despite, the coupling between geomagnetic and solar wind parameters, the results show that each parameter still carries a sufficient amount of unique information to more accurately constrain the chorus and plasmaspheric hiss wave intensities. The new wave models presented here highlight the importance of multi-parameter wave models, and can improve radiation belt modeling. Aryan, Homayon; Bortnik, Jacob; Meredith, Nigel; Horne, Richard; Sibeck, David; Balikhin, Michael; Published by: Journal of Geophysical Research: Space Physics Published on: 12/2020 YEAR: 2020 DOI: https://doi.org/10.1029/2020JA028403 chorus waves; inner magnetosphere; multi parameter wave distribution; plasmaspheric hiss waves; Van Allen Probes; wave-particle interactions |
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Abstract Forecasting relativistic electron fluxes at geostationary Earth orbit (GEO) has been a long-term goal of the scientific community, and significant advances have been made in the past, but the relation to the interior of the radiation belts, that is, to lower L-shells, is still not clear. In this work we have identified 60 relativistic electron enhancement events at GEO to study the radial response of outer belt fluxes and the correlation between the fluxes at GEO and those at lower L-shells. The enhancement events occurred between 1 October 2012 and 31 December 2017 and were identified using Geostationary Operational Environmental Satellite (GOES) 15 >2 MeV fluxes at GEO, which we have used to characterize the radial response of the radiation belt, by comparing to fluxes measured by the Van Allen probes Energetic Particle, Composition and Thermal Plasma Suite Relativistic Electron-Proton Telescope (ECT-REPT) between 2.5 Pinto, Victor; Bortnik, Jacob; Moya, Pablo; Lyons, Larry; Sibeck, David; Kanekal, Shrikanth; Spence, Harlan; Baker, Daniel; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2020 YEAR: 2020 DOI: 10.1029/2019JA027660 Radiation belts; relativistic electrons; geosynchronous orbit; Outer Belt; flux correlation; enhancement events; Van Allen Probes |
| 2019 |
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Electromagnetic ion cyclotron (EMIC) waves are understood to be one of the dominant drivers of relativistic electron loss from Earth\textquoterights radiation belts. Theory predicts that the associated gyroresonant wave-particle interaction results in a distinct energy-dependent \textquotedblleftbite-out\textquotedblright signature in the normalized flux distribution of electrons as they are scattered into the loss cone. We identify such signatures along with the responsible EMIC waves captured in situ by the Van Allen Probes on 15\textendash16 February 2017. Using the cold plasma approximation, we predict the pitch-angle cutoffs for the scattering signature for the captured EMIC wave and find it in good agreement with the observed electron bite-out scattering signature. Employing the close conjunction between the Van Allen Probes and THEMIS during this time, we explore the temporal and spatial evolution of the scattering signature, as well as the surrounding wave activity, and find that the scattering signature formed during continued wave activity over a period less than a day. These results are consistent with wave-particle interaction theory and support the hypothesis that EMIC waves are an important mechanism for rapid relativistic electron loss from the radiation belts. Bingley, L.; Angelopoulos, V.; Sibeck, D.; Zhang, X.; Halford, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2019 YEAR: 2019 DOI: 10.1029/2018JA026292 |
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Energy coupling between the solar wind and the Earth\textquoterights magnetosphere can affect the electron population in the outer radiation belt. However, the precise role of different internal and external mechanisms that leads to changes of the relativistic electron population is not entirely known. This paper describes how Ultra Low Frequency (ULF) wave activity during the passage of Alfv\ enic solar wind streams contributes to the global recovery of the relativistic electron population in the outer radiation belt. To investigate the contribution of the ULF waves, we searched the Van Allen Probes data for a period in which we can clearly distinguish the enhancement of electron fluxes from the background. We found that the global recovery that started on September 22, 2014, which coincides with the corotating interaction region preceding a high-speed stream and the occurrence of persistent substorm activity, provides an excellent scenario to explore the contribution of ULF waves. To support our analyses, we employed ground and space-based observational data, global magnetohydrodynamic (MHD) simulations, and calculated the ULF wave radial diffusion coefficients employing an empirical model. Observations show a gradual increase of electron fluxes in the outer radiation belt and a concomitant enhancement of ULF activity that spreads from higher to lower L-shells. MHD simulation results agree with observed ULF wave activity in the magnetotail, which leads to both fast and Alfv\ en modes in the magnetospheric nightside sector. The observations agree with the empirical model and are confirmed by Phase Space Density (PhSD) calculations for this global recovery period. Da Silva, L.; Sibeck, D.; Alves, L.; Souza, V.; Jauer, P.; Claudepierre, S.; Marchezi, J.; Agapitov, O.; Medeiros, C.; Vieira, L.; Wang, C.; Jiankui, S.; Liu, Z.; Gonzalez, W.; Dal Lago, A.; Rockenbach, M.; Padua, M.; Alves, M.; Barbosa, M.; Fok, M.-C.; Baker, D.; Kletzing, C.; Kanekal, S.; Georgiou, M.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2019 YEAR: 2019 DOI: 10.1029/2018JA026184 alfv\ en fluctuations; Earth\textquoterights magnetosphere; high speed stream; Radiation belts; relativistic electron flux; ULF wave; Van Allen Probes |
| 2018 |
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Shortly after the launch of the Van Allen Probes, a new three-belt configuration of the electron radiation belts was reported. Using data between September 2012 and November 2017, we have identified 30 three-belt events and found that about 18\% of geomagnetic storms result in such configuration. Based on the identified events, we evaluated some characteristics of the remnant (intermediate) belt. We determined the energy range of occurrence and found it peaks at E = 5.2 MeV. We also determined that the magnetopause location and SYM-H value may play an important role in the outer belt losses that lead to formation and location of the remnant belt. Finally, we calculated the decay rates of the remnant belt for all events and found that their lifetime gets longer as energy increases, ranging from days at E = 1.8 MeV up to months at E = 6.3 MeV suggesting that remnant belts are extremely persistent. Pinto, V\; Bortnik, Jacob; Moya, Pablo; Lyons, Larry; Sibeck, David; Kanekal, Shrikanth; Spence, Harlan; Baker, Daniel; Published by: Geophysical Research Letters Published on: 10/2018 YEAR: 2018 DOI: 10.1029/2018GL080274 Belt Formation; MeV Electrons; Outer Belt; Radiation belts; Remnant Belt; Three Belts; Van Allen Probes |
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Ion Injection Triggered EMIC Waves in the Earth\textquoterights Magnetosphere We present Van Allen Probe observations of electromagnetic ion cyclotron (EMIC) waves triggered solely due to individual substorm-injected ions in the absence of storms or compressions of the magnetosphere during 9 August 2015. The time at which the injected ions are observed directly corresponds to the onset of EMIC waves at the location of Van Allen Probe A (L = 5.5 and 18:06 magnetic local time). The injection was also seen at geosynchronous orbit by the Geostationary Operational Environmental Satellite and Los Alamos National Laboratory spacecraft, and the westward(eastward) drift of ions(electrons) was monitored by Los Alamos National Laboratory spacecraft at different local times. The azimuthal location of the injection was determined by tracing the injection signatures backward in time to their origin assuming a dipolar magnetic field of Earth. The center of this injection location was determined to be close to \~20:00 magnetic local time. Geostationary Operational Environmental Satellite and ground magnetometer responses confirm substorm onset at approximately the same local time. The observed EMIC wave onsets at Van Allen Probe were also associated with a magnetic field decrease. The arrival of anisotropic ions along with the decrease in the magnetic field favors the growth of the EMIC wave instability based on linear theory analysis. Remya, B.; Sibeck, D.; Halford, A.; Murphy, K.; Reeves, G.; Singer, H.; Wygant, J.; Perez, Farinas; Thaller, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2018 YEAR: 2018 DOI: 10.1029/2018JA025354 EMIC waves; Ion injections; magnetic dip; substorm; Van Allen Probes |
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Ultra-low frequency (ULF) waves play a fundamental role in the dynamics of the inner-magnetosphere and outer radiation belt during geomagnetic storms. Broadband ULF wave power can transport energetic electrons via radial diffusion and discrete ULF wave power can energize electrons through a resonant interaction. Using observations from the Magnetospheric Multiscale (MMS) mission, we characterize the evolution of ULF waves during a high-speed solar wind stream (HSS) and moderate geomagnetic storm while there is an enhancement of the outer radiation belt. The Automated Flare Inference of Oscillations (AFINO) code is used to distinguish discrete ULF wave power from broadband wave power during the HSS. During periods of discrete wave power and utilizing the close separation of the MMS spacecraft, we estimate the toroidal mode ULF azimuthal wave number throughout the geomagnetic storm. We concentrate on the toroidal mode as the HSSs compresses the day side magnetosphere resulting in an asymmetric magnetic field topology where toroidal mode waves can interact with energetic electrons. Analysis of the mode structure and wave numbers demonstrates that the generation of the observed ULF waves is a combination of externally driven waves, via the Kelvin-Helmholtz instability, and internally driven waves, via unstable ion distributions. Further analysis of the periods and toroidal azimuthal wave numbers suggests that these waves can couple with the core electron radiation belt population via the drift resonance during the storm. The azimuthal wave number and structure of ULF wave power (broadband or discrete) have important implications for the inner-magnetospheric and radiation belt dynamics. Murphy, Kyle; Inglis, Andrew; Sibeck, David; Rae, Jonathan; Watt, Clare; Silveira, Marcos; Plaschke, Ferdinand; Claudepierre, Seth; Nakamura, Rumi; Published by: Journal of Geophysical Research: Space Physics Published on: 05/2018 YEAR: 2018 DOI: 10.1029/2017JA024877 azimuthal wave number; Geomagnetic storms; mode structure; Radiation belts; ULF waves; Van Allen Probes |
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The global statistical response of the outer radiation belt during geomagnetic storms Using the total radiation belt electron content calculated from Van Allen Probe phase space density (PSD), the time-dependent and global response of the outer radiation belt during storms is statistically studied. Using PSD reduces the impacts of adiabatic changes in the main phase, allowing a separation of adiabatic and non-adiabatic effects, and revealing a clear modality and repeatable sequence of events in storm-time radiation belt electron dynamics. This sequence exhibits an important first adiabatic invariant (μ) dependent behaviour in the seed (150 MeV/G), relativistic (1000 MeV/G), and ultra-relativistic (4000 MeV/G) populations. The outer radiation belt statistically shows an initial phase dominated by loss followed by a second phase of rapid acceleration, whilst the seed population shows little loss and immediate enhancement. The time sequence of the transition to the acceleration is also strongly μ-dependent and occurs at low μ first, appearing to be repeatable from storm to storm. Murphy, Kyle; Watt, C.; Mann, Ian; Rae, Jonathan; Sibeck, David; Boyd, A.; Forsyth, C.; Turner, D.; Claudepierre, S.; Baker, D.; Spence, H.; Reeves, G.; Blake, J.; Fennell, J.; Published by: Geophysical Research Letters Published on: 04/2018 YEAR: 2018 DOI: 10.1002/2017GL076674 Geomagnetic storms; magnetospheric dynamics; Radiation belts; Solar Wind-Magnetosphere Coupling; statistical analysis; Van Allen Probes |
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Space Weather Operation at KASI with Van Allen Probes Beacon Signals The Van Allen Probes (VAPs) are the only modern NASA spacecraft broadcasting real-time data on the Earth\textquoterights radiation belts for space weather operations. Since 2012, the Korea Astronomy and Space Science Institute (KASI) has contributed to the receipt of this data via a 7-m satellite tracking antenna and used these data for space weather operations. An approximately 15-min period is required from measurement to acquisition of Level-1 data. In this paper, we demonstrate the use of VAP data for monitoring space weather conditions at geostationary orbit (GEO) by highlighting the Saint Patrick\textquoterights Day storm of 2015. During that storm, Probe-A observed a significant increase in the relativistic electron flux at 3 RE. Those electrons diffused outward resulting in a large increase of the electron flux > 2 MeV at GEO, which potentially threatened satellite operations. Based on this study, we conclude that the combination of VAP data and National Oceanic and Atmospheric Administration-Geostationary Operational Environmental Satellite (NOAA-GOES) data can provide improved space environment information to geostationary satellite operators. In addition, the findings obtained indicate that more data-receiving sites would be necessary and data connections improved if this or a similar system were to be used as an operational data service. Lee, Jongkil; Kim, Kyung-Chan; Romeo, Giuseppe; Ukhorskiy, Sasha; Sibeck, David; Kessel, Ramona; Mauk, Barry; Giles, Barbara; Gu, Bon-Jun; Lee, Hyesook; Park, Young-Deuk; Lee, Jaejin; Published by: Space Weather Published on: 01/2018 YEAR: 2018 DOI: 10.1002/2017SW001726 Electron acceleration; Radiation belt; Relativistic electron; Space weather; Van Allen Probes |
| 2017 |
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Using Van Allen Probes ECT-REPT observations we performed a statistical study on the effect of geomagnetic storms on relativistic electrons fluxes in the outer radiation belt for 78 storms between September 2012 and June 2016. We found that the probability of enhancement, depletion and no change in flux values depends strongly on L and energy. Enhancement events are more common for \~ 2 MeV electrons at L \~ 5, and the number of enhancement events decreases with increasing energy at any given L shell. However, considering the percentage of occurrence of each kind of event, enhancements are more probable at higher energies, and the probability of enhancement tends to increases with increasing L shell. Depletion are more probable for 4-5 MeV electrons at the heart of the outer radiation belt, and no change events are more frequent at L < 3.5 for E\~ 3 MeV particles. Moreover, for L > 4.5 the probability of enhancement, depletion or no-change response presents little variation for all energies. Because these probabilities remain relatively constant as a function of radial distance in the outer radiation belt, measurements obtained at Geosynchronous orbit may be used as a proxy to monitor E>=1.8 MeV electrons in the outer belt. Moya, Pablo.; Pinto, \; Sibeck, David; Kanekal, Shrikanth; Baker, Daniel; Published by: Journal of Geophysical Research: Space Physics Published on: 10/2017 YEAR: 2017 DOI: 10.1002/2017JA024735 Geomagnetic storms; Radiation belts; relativistic electrons; Van Allen Probes |
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In this study we examine the recovery of relativistic radiation belt electrons on November 15-16, 2014, after a previous reduction in the electron flux resulting from the passage of a Corotating Interaction Region (CIR). Following the CIR, there was a period of high-speed streams characterized by large, nonlinear fluctuations in the interplanetary magnetic field (IMF) components. However, the outer radiation belt electron flux remained at a low level for several days before it increased in two major steps. The first increase is associated with the IMF background field turning from slightly northward on average, to slightly southward on average. The second major increase is associated with an increase in the solar wind velocity during a period of southward average IMF background field. We present evidence that when the IMF Bz is negative on average, the whistler mode chorus wave power is enhanced in the outer radiation belt, and the amplification of magnetic integrated power spectral density in the ULF frequency range, in the nightside magnetosphere, is more efficient as compared to cases in which the mean IMF Bz is positive. Preliminary analysis of the time evolution of phase space density radial profiles did not provide conclusive evidence on which electron acceleration mechanism is the dominant. We argue that the acceleration of radiation belt electrons requires (i) a seed population of keV electrons injected into the inner magnetosphere by substorms, and both (ii) enhanced whistler mode chorus waves activity as well as (iii) large-amplitude MHD waves. Souza, V.; Lopez, R.; Jauer, P.; Sibeck, D.; Pham, K.; Silva, L.; Marchezi, J.; Alves, L.; Koga, D.; Medeiros, C.; Rockenbach, M.; Gonzalez, W.; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2017 YEAR: 2017 DOI: 10.1002/2017JA024187 Electron acceleration; High-speed solar wind streams; IMF Bz fluctuations; Outer Van Allen belt; Van Allen Probes |
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CIMI simulations with newly developed multi-parameter chorus and plasmaspheric hiss wave models Numerical simulation studies of the Earth\textquoterights radiation belts are important to understand the acceleration and loss of energetic electrons. The Comprehensive Inner Magnetosphere-Ionosphere (CIMI) model considers the effects of the ring current and plasmasphere on the radiation belts to obtain plausible results. The CIMI model incorporates pitch angle, energy, and cross diffusion of electrons, due to chorus and plasmaspheric hiss waves. These parameters are calculated using statistical wave distribution models of chorus and plasmaspheric hiss amplitudes. However, currently these wave distribution models are based only on a single parameter, geomagnetic index (AE), and could potentially underestimate the wave amplitudes. Here we incorporate recently developed multi-parameter chorus and plasmaspheric hiss wave models based on geomagnetic index and solar wind parameters. We then perform CIMI simulations for two geomagnetic storms and compare the flux enhancement of MeV electrons with data from the Van Allen Probes and Akebono satellites. We show that the relativistic electron fluxes calculated with multi-parameter wave models resembles the observations more accurately than the relativistic electron fluxes calculated with single-parameter wave models. This indicates that wave models based on a combination of geomagnetic index and solar wind parameters are more effective as inputs to radiation belt models. Aryan, Homayon; Sibeck, David; Bin Kang, Suk-; Balikhin, Michael; Fok, Mei-Ching; Agapitov, Oleksiy; Komar, Colin; Kanekal, Shrikanth; Nagai, Tsugunobu; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2017 YEAR: 2017 DOI: 10.1002/2017JA024159 Chorus and plasmaspheric hiss wave models; CIMI numerical simulations; Geomagnetic storm events; Radiation belt electron flux enhancements; Van Allen Probes; VLF waves; Wave-particle interaction |
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In September 2014 an unusually long-lasting (≳10 days) ultra-relativistic electron flux depletion occurred in the outer radiation belt despite ongoing solar wind forcing. We simulate this period using a ULF wave radial diffusion model, driven by observed ULF wave power coupled to flux variations at the outer boundary at L* = 5, including empirical electron loss models due to chorus and hiss wave scattering. Our results show that unexplained rapid main phase loss, that depletes the belt within hours, is essential to explain the observations. Such ultra-relativistic electron extinction decouples the prestorm and poststorm fluxes, revealing the subsequent belt dynamics to be surprisingly independent of prestorm flux. However, once this extinction is included, ULF wave transport and coupling to the outer boundary explain the extended depletion event and also the eventual flux recovery. Neither local acceleration nor ongoing losses from hiss or chorus wave scattering to the atmosphere are required. Ozeke, Louis; Mann, Ian; Murphy, Kyle; Sibeck, David; Baker, Daniel; Published by: Geophysical Research Letters Published on: 03/2017 YEAR: 2017 DOI: 10.1002/2017GL072811 radial diffusion; Radiation belt; ULF waves; ultrarelativistic; Van Allen Probes; wave-particle interactions |
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We analyze a wave event that occurred near noon between 07:03 and 07:08 UT on 23 February 2014 detected by the Van Allen Probes B spacecraft, where waves in the lower hybrid frequency range (LHFR) and electromagnetic ion cyclotron (EMIC) waves are observed to be highly correlated, with Pearson correlation coefficient of ~0.86. We assume that the correlation is the result of LHFR wave generation by the ions\textquoteright polarization drift in the electric field of the EMIC waves. To check this assumption the drift velocities of electrons and H+, He+, and O+ ions in the measured EMIC wave electric field were modeled. Then the LHFR wave linear instantaneous growth rates for plasma with these changing drift velocities and different plasma compositions were calculated. The time distribution of these growth rates, their frequency distribution, and the frequency dependence of the ratio of the LHFR wave power spectral density (PSD) parallel and perpendicular to the ambient magnetic field to the total PSD were found. These characteristics of the growth rates were compared with the corresponding characteristics of the observed LHFR activity. Reasonable agreement between these features and the strong correlation between EMIC and LHFR energy densities support the assumption that the LHFR wave generation can be caused by the ions\textquoteright polarization drift in the electric field of an EMIC wave. Khazanov, G.; Boardsen, S.; Krivorutsky, E.; Engebretson, M.; Sibeck, D.; Chen, S.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA022814 nonlinear phenomena; parametric processes; Van Allen Probes; wave/wave interactions |
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We analyze a wave event that occurred near noon between 07:03 and 07:08 UT on 23 February 2014 detected by the Van Allen Probes B spacecraft, where waves in the lower hybrid frequency range (LHFR) and electromagnetic ion cyclotron (EMIC) waves are observed to be highly correlated, with Pearson correlation coefficient of ~0.86. We assume that the correlation is the result of LHFR wave generation by the ions\textquoteright polarization drift in the electric field of the EMIC waves. To check this assumption the drift velocities of electrons and H+, He+, and O+ ions in the measured EMIC wave electric field were modeled. Then the LHFR wave linear instantaneous growth rates for plasma with these changing drift velocities and different plasma compositions were calculated. The time distribution of these growth rates, their frequency distribution, and the frequency dependence of the ratio of the LHFR wave power spectral density (PSD) parallel and perpendicular to the ambient magnetic field to the total PSD were found. These characteristics of the growth rates were compared with the corresponding characteristics of the observed LHFR activity. Reasonable agreement between these features and the strong correlation between EMIC and LHFR energy densities support the assumption that the LHFR wave generation can be caused by the ions\textquoteright polarization drift in the electric field of an EMIC wave. Khazanov, G.; Boardsen, S.; Krivorutsky, E.; Engebretson, M.; Sibeck, D.; Chen, S.; Breneman, A.; Published by: Journal of Geophysical Research: Space Physics Published on: 01/2017 YEAR: 2017 DOI: 10.1002/2016JA022814 nonlinear phenomena; parametric processes; Van Allen Probes; wave/wave interactions |
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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 |
| 2016 |
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Highly energetic electrons in the Earth\textquoterights Van Allen radiation belts can cause serious damage to spacecraft electronic systems and affect the atmospheric composition if they precipitate into the upper atmosphere. Whistler mode chorus waves have attracted significant attention in recent decades for their crucial role in the acceleration and loss of energetic electrons that ultimately change the dynamics of the radiation belts. The distribution of these waves in the inner magnetosphere is commonly presented as a function of geomagnetic activity. However, geomagnetic indices are nonspecific parameters that are compiled from imperfectly covered ground based measurements. The present study uses wave data from the two Van Allen Probes to present the distribution of lower band chorus waves not only as functions of single geomagnetic index and solar wind parameters but also as functions of combined parameters. Also the current study takes advantage of the unique equatorial orbit of the Van Allen Probes to estimate the average scale size of chorus wave packets, during close separations between the two spacecraft, as a function of radial distance, magnetic latitude, and geomagnetic activity, respectively. Results show that the average scale size of chorus wave packets is approximately 1300\textendash2300 km. The results also show that the inclusion of combined parameters can provide better representation of the chorus wave distributions in the inner magnetosphere and therefore can further improve our knowledge of the acceleration and loss of radiation belt electrons. Aryan, Homayon; Sibeck, David; Balikhin, Michael; Agapitov, Oleksiy; Kletzing, Craig; Published by: Journal of Geophysical Research: Space Physics Published on: 08/2016 YEAR: 2016 DOI: 10.1002/jgra.v121.810.1002/2016JA022775 distribution of chorus wave intensities in the inner magnetosphere; inner magnetosphere; Radiation belts; scale size of chorus wave packets; Van Allen Probes; Wave-particle interaction |
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Analysis of particle pitch angle distributions (PADs) has been used as a means to comprehend a multitude of different physical mechanisms that lead to flux variations in the Van Allen belts and also to particle precipitation into the upper atmosphere. In this work we developed a neural network-based data clustering methodology that automatically identifies distinct PAD types in an unsupervised way using particle flux data. One can promptly identify and locate three well-known PAD types in both time and radial distance, namely, 90\textdegree peaked, butterfly, and flattop distributions. In order to illustrate the applicability of our methodology, we used relativistic electron flux data from the whole month of November 2014, acquired from the Relativistic Electron-Proton Telescope instrument on board the Van Allen Probes, but it is emphasized that our approach can also be used with multiplatform spacecraft data. Our PAD classification results are in reasonably good agreement with those obtained by standard statistical fitting algorithms. The proposed methodology has a potential use for Van Allen belt\textquoterights monitoring. Souza, V.; Vieira, L.; Medeiros, C.; Da Silva, L.; Alves, L.; Koga, D.; Sibeck, D.; Walsh, B.; Kanekal, S.; Jauer, P.; Rockenbach, M.; Dal Lago, A.; Silveira, M.; Marchezi, J.; Mendes, O.; Gonzalez, W.; Baker, D.; Published by: Space Weather Published on: 04/2016 YEAR: 2016 DOI: 10.1002/2015SW001349 pitch angle distributions; self-organizing maps; Van Allen belt\textquoterights monitoring; Van Allen Probes |
| 2015 |
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Electron distribution function formation in regions of diffuse aurora The precipitation of high-energy magnetospheric electrons (E \~ 600 eV\textendash10 KeV) in the diffuse aurora contributes significant energy flux into the Earth\textquoterights ionosphere. To fully understand the formation of this flux at the upper ionospheric boundary, \~700\textendash800 km, it is important to consider the coupled ionosphere-magnetosphere system. In the diffuse aurora, precipitating electrons initially injected from the plasma sheet via wave-particle interaction processes degrade in the atmosphere toward lower energies and produce secondary electrons via impact ionization of the neutral atmosphere. These precipitating electrons can be additionally reflected upward from the two conjugate ionospheres, leading to a series of multiple reflections through the magnetosphere. These reflections greatly influence the initially precipitating flux at the upper ionospheric boundary (700\textendash800 km) and the resultant population of secondary electrons and electrons cascading toward lower energies. In this paper, we present the solution of the Boltzman-Landau kinetic equation that uniformly describes the entire electron distribution function in the diffuse aurora, including the affiliated production of secondary electrons (E < 600 eV) and its energy interplay in the magnetosphere and two conjugated ionospheres. This solution takes into account, for the first time, the formation of the electron distribution function in the diffuse auroral region, beginning with the primary injection of plasma sheet electrons via both electrostatic electron cyclotron harmonic waves and whistler mode chorus waves to the loss cone, and including their subsequent multiple atmospheric reflections in the two magnetically conjugated ionospheres. It is demonstrated that magnetosphere-ionosphere coupling is key in forming the electron distribution function in the diffuse auroral region. Khazanov, G.; Tripathi, A.; Sibeck, D.; Himwich, E.; Glocer, A.; Singhal, R.; Published by: Journal of Geophysical Research: Space Physics Published on: 11/2015 YEAR: 2015 DOI: 10.1002/2015JA021728 diffuse aurora; electron distribution; Wave-particle interaction |
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Turbulence is complex behavior that is ubiquitous in nature, but its mechanism is still not sufficiently clear. Therefore, the main aim of this paper is analysis of intermittent turbulence in magnetospheric and solar wind plasmas using a statistical approach based on experimental data acquired from space missions. The quintet spacecraft of Time History of Events and Macroscale Interactions during Substorms (THEMIS) allows us to investigate the details of turbulent plasma parameters behind the collisionless shocks. We investigate both the solar wind and magnetospheric data by using statistical probability distribution functions of Elsässer variables that can reveal the intermittent character of turbulence in space plasma. Our results suggest that turbulence behind the quasi-perpendicular shock is more intermittent with larger kurtosis than that behind the quasi-parallel shocks, which are immersed in a relatively quiet solar wind plasma, as confirmed by Wind measurements. It seems that behind the quasi-perpendicular shock the waves propagating outward from the Sun are larger than possibly damped waves propagating inward. In particular, we hope that this difference in characteristic behavior of the fluctuating space plasma parameters behind both types of shocks can help identify complex plasma structures in the future space missions. We also expect that the results obtained in this paper will be important for general models of turbulence. Macek, W.; Wawrzaszek, A.; Sibeck, D.; Published by: Journal of Geophysical Research: Space Physics Published on: 09/2015 YEAR: 2015 DOI: 10.1002/2015JA021656 intermittency; magnetosheath; shocks; Solar wind; Space plasma; turbulence |
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n the dawn sector, L~ 5.5 and MLT~4-7, from 01:30 to 06:00 UT during the November 14th 2012 geomagnetic storm, both Van Allen Probes observed an alternating sequence of locally quiet and disturbed intervals with two strikingly different power fluctuation levels and magnetic field orientations: either small (~10-2 nT2) total power with strong GSM Bx and weak By, or large (~10 nT2) total power with weak Bx, and strong By and Bz components. During both kinds of intervals the fluctuations occur in the vicinity of the local ion gyro-frequencies (0.01-10 Hz) in the spacecraft frame, propagate oblique to the magnetic field, (θ ~ 60\textdegree) and have magnetic compressibility C = |δB|||/|δB⊥| \~ 1, where δB|| (δB⊥) are the average amplitudes of the fluctuations parallel (perpendicular) to the mean field. Electric field fluctuations are present whenever the magnetic field is disturbed, and large electric field fluctuations follow the same pattern for quiet and disturbed intervals. Magnetic frequency power spectra at both spacecraft correspond to steep power-laws \~ f \textendashα with 4 < α < 5 for f ≲ 2 Hz, and 1.1 < α < 1.7 for f ≲ 2 Hz, spectral profiles that are consistent with weak Kinetic Alfv\ en Waves (KAW) turbulence. Electric power is larger than magnetic power for all frequencies above 0.1 Hz, and the ratio increases with increasing frequency. Vlasov linear analysis is consistent with the presence of compressive KAW with k⊥ρi ≲ 1, right-handed polarization and positive magnetic helicity, in the plasma frame, considering a multi-ion plasma. All these results suggest the presence of weak KAW turbulence which dissipates the energy associated with the intermittent sudden changes in the magnetic field during the main phase of the storm. Moya, Pablo.; Pinto, V\; Vi\~nas, Adolfo; Sibeck, David; Kurth, William; Hospodarsky, George; Wygant, John; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2015 YEAR: 2015 DOI: 10.1002/2014JA020281 Kinetic Alfven Waves; Magnetic Storms; Radiation belts; Van Allen Probes |
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The global context of the 14 November, 2012 storm event From 2 to 5 UT on 14 November, 2012, the Van Allen Probes observed repeated particle flux dropouts during the main phase of a geomagnetic storm as the satellites traversed the post-midnight to dawnside inner magnetosphere. Each flux dropout corresponded to an abrupt change in the magnetic topology, i.e., from a more dipolar configuration to a configuration with magnetic field lines stretched in the dawn-dusk direction. Geosynchronous GOES spacecraft located in the dusk and near-midnight sectors and the LANL constellation with wide local time coverage also observed repeated flux dropouts and stretched field lines with similar occurrence patterns to those of the Van Allen Probe events. THEMIS recorded multiple transient abrupt expansions of the evening-side magnetopause ~20\textendash30 min prior to the sequential Van Allen Probes observations. Ground-based magnetograms and all sky images demonstrate repeatable features in conjunction with the dropouts. We combine the various in-situ and ground-based measurements to define and understand the global spatiotemporal features associated with the dropouts observed by the Van Allen Probes. We discuss various proposed hypotheses for the mechanism that plausibly caused this storm-time dropout event as well as formulate a new hypothesis that explains the combined in-situ and ground-based observations: the earthward motion of magnetic flux ropes containing lobe plasmas that form along an extended magnetotail reconnection line in the near-Earth plasma sheet. Hwang, K.-J.; Sibeck, D.; Fok, M.-C.; Zheng, Y.; Nishimura, Y.; Lee, J.-J.; Glocer, A.; Partamies, N.; Singer, H.; Reeves, G.; Mitchell, D.; Kletzing, C.; Onsager, T.; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2015 YEAR: 2015 DOI: 10.1002/2014JA020826 |
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We present Van Allen Probe B observations of azimuthally limited, antisymmetric, poloidal Pc 4 electric and magnetic field pulsations in the pre-midnight sector of the magnetosphere from 05:40 to 06:00 UT on 1 May 2013. Oscillation periods were similar for the magnetic and electric fields and proton fluxes. The flux of energetic protons exhibited an energy-dependent response to the pulsations. Energetic proton variations were anticorrelated at medium and low energies. Although we attribute the pulsations to a drift-bounce resonance, we demonstrate that the energy-dependent response of the ion fluxes results from pulsation-associated velocities sweeping energy-dependent radial ion flux gradients back and forth past the spacecraft. Korotova, G.; Sibeck, D.; Tahakashi, K.; Dai, L.; Spence, H.; Kletzing, C.; Wygant, J.; Manweiler, J.; Moya, P.; Hwang, K.-J.; Redmon, R.; Published by: Annales Geophysicae Published on: 01/2015 YEAR: 2015 DOI: 10.5194/angeo-33-955-2015 |
| 2014 |
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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 |
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Journal Special Collection Explores Early Results From the Van Allen Probes Mission The processes governing the charged particle populations in the radiation belts encircling Earth have been the subject of intense interest and increasing concern since their discovery by James Van Allen and his team more than 50 years ago [Baker et al., 2013]. Intense interest continues because we still do not know how the various processes work in concert to enhance, remove, and transport particle radiation. Concern is ongoing because the Van Allen radiation belts pose hazards to astronauts and our ever-growing fleet of spacecraft with increasingly sensitive components. Mauk, Barry; Sibeck, David; Kessel, Ramona; Published by: Eos, Transactions American Geophysical Union Published on: 04/2014 YEAR: 2014 DOI: 10.1002/eost.v95.1310.1002/2014EO130007 |
| 2013 |
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Science Objectives and Rationale for the Radiation Belt Storm Probes Mission The NASA Radiation Belt Storm Probes (RBSP) mission addresses how populations of high energy charged particles are created, vary, and evolve in space environments, and specifically within Earth\textquoterights magnetically trapped radiation belts. RBSP, with a nominal launch date of August 2012, comprises two spacecraft making in situ measurements for at least 2 years in nearly the same highly elliptical, low inclination orbits (1.1\texttimes5.8 RE, 10o). The orbits are slightly different so that 1 spacecraft laps the other spacecraft about every 2.5 months, allowing separation of spatial from temporal effects over spatial scales ranging from \~0.1 to 5 RE. The uniquely comprehensive suite of instruments, identical on the two spacecraft, measures all of the particle (electrons, ions, ion composition), fields (E and B), and wave distributions (d E and d B) that are needed to resolve the most critical science questions. Here we summarize the high level science objectives for the RBSP mission, provide historical background on studies of Earth and planetary radiation belts, present examples of the most compelling scientific mysteries of the radiation belts, present the mission design of the RBSP mission that targets these mysteries and objectives, present the observation and measurement requirements for the mission, and introduce the instrumentation that will deliver these measurements. This paper references and is followed by a number of companion papers that describe the details of the RBSP mission, spacecraft, and instruments. Mauk, B.; Fox, N.; Kanekal, S.; Kessel, R.; Sibeck, D.; UKHORSKIY, A; Published by: Space Science Reviews Published on: 11/2013 YEAR: 2013 DOI: 10.1007/s11214-012-9908-y |
| 2011 |
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Radiation belt storm probes: Resolving fundamental physics with practical consequences The fundamental processes that energize, transport, and cause the loss of charged particles operate throughout the universe at locations as diverse as magnetized planets, the solar wind, our Sun, and other stars. The same processes operate within our immediate environment, the Earth\textquoterights radiation belts. The Radiation Belt Storm Probes (RBSP) mission will provide coordinated two-spacecraft observations to obtain understanding of these fundamental processes controlling the dynamic variability of the near-Earth radiation environment. In this paper we discuss some of the profound mysteries of the radiation belt physics that will be addressed by RBSP and briefly describe the mission and its goals. Ukhorskiy, Aleksandr; Mauk, Barry; Fox, Nicola; Sibeck, David; Grebowsky, Joseph; Published by: Journal of Atmospheric and Solar-Terrestrial Physics Published on: 07/2011 YEAR: 2011 DOI: 10.1016/j.jastp.2010.12.005 |
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