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Found 1109 entries in the Bibliography.
Showing entries from 901 through 950
| 2014 |
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Although magnetospheric chorus plays a significant role in the acceleration and loss of radiation belt electrons, its global evolution during any specific time period cannot be directly obtained by spacecraft measurements. Using the low-altitude NOAA Polar-orbiting Operational Environmental Satellite (POES) electron data, we develop a novel physics-based methodology to infer the chorus wave intensity and construct its global distribution with a time resolution of less than an hour. We describe in detail how to apply the technique to satellite data by performing two representative analyses, i.e., (i) for one specific time point to visualize the estimation procedure and (ii) for a particular time period to validate the method and construct an illustrative global chorus wave model. We demonstrate that the spatiotemporal evolution of chorus intensity in the equatorial magnetosphere can be reasonably estimated from electron flux measurements made by multiple low-altitude POES satellites with a broad coverage of L shell and magnetic local time. Such a data-based, dynamic model of chorus waves can provide near-real-time wave information on a global scale for any time period where POES electron data are available. A combination of the chorus wave spatiotemporal distribution acquired using this methodology and the direct spaceborne wave measurements can be used to evaluate the quantitative scattering caused by resonant wave-particle interactions and thus model radiation belt electron variability. Ni, Binbin; Li, Wen; Thorne, Richard; Bortnik, Jacob; Green, Janet; Kletzing, Craig; Kurth, William; Hospodarsky, George; Pich, Maria; Published by: Journal of Geophysical Research: Space Physics Published on: 07/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.710.1002/2014JA019935 electron precipitation; global wave distribution; magnetospheric chorus; physics-based technique; wave resonant scattering |
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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 |
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Excitation of EMIC waves detected by the Van Allen Probes on 28 April 2013 We report the wave observations, associated plasma measurements, and linear theory testing of electromagnetic ion cyclotron (EMIC) wave events observed by the Van Allen Probes on 28 April 2013. The wave events are detected in their generation regions as three individual events in two consecutive orbits of Van Allen Probe-A, while the other spacecraft, B, does not detect any significant EMIC wave activity during this period. Three overlapping H+ populations are observed around the plasmapause when the waves are excited. The difference between the observational EMIC wave growth parameter (Σh) and the theoretical EMIC instability parameter (Sh) is significantly raised, on average, to 0.10 \textpm 0.01, 0.15 \textpm 0.02, and 0.07 \textpm 0.02 during the three wave events, respectively. On Van Allen Probe-B, this difference never exceeds 0. Compared to linear theory (Σh > Sh), the waves are only excited for elevated thresholds. Zhang, J.-C.; Saikin, A.; Kistler, L.; Smith, C.; Spence, H.; Mouikis, C.; Torbert, R.; Larsen, B.; Reeves, G.; Skoug, R.; Funsten, H.; Kurth, W.; Kletzing, C.; Allen, R.; Jordanova, V.; Published by: Geophysical Research Letters Published on: 06/2014 YEAR: 2014 DOI: 10.1002/2014GL060621 |
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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 |
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We report large directional anisotropies of >60 MeV protons using instrumentation on the Van Allen Probes. The combination of a spinning satellite and measurements from the Relativistic Proton Spectrometer instruments that are insensitive to protons outside the instrument field of view together yield a new look at proton radial gradients. The relatively large proton gyroradius at 60 MeV couples with the radial gradients to produce large (maximum ~10:1) flux anisotropies depending on (i) whether the proton guiding center was above or below the Van Allen Probes spacecraft and (ii) the sign of the local flux gradient. In addition to these newly measured anisotropies, below ~2000 km we report a new effect of systematically changing minimum altitude on some proton drift shells that further modulates the anisotropy caused by the atmosphere. This discovery may offer a new way of monitoring changes to the loss of inner belt protons into the Earth\textquoterights atmosphere. Mazur, J.; O\textquoterightBrien, T.; Looper, M.; Blake, J.; Published by: Geophysical Research Letters Published on: 06/2014 YEAR: 2014 DOI: 10.1002/grl.v41.1110.1002/2014GL060029 |
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Radiation belt electron acceleration by chorus waves during the 17 March 2013 storm Local acceleration driven by whistler-mode chorus waves is fundamentally important for accelerating seed electron populations to highly relativistic energies in the outer radiation belt. In this study, we quantitatively evaluate chorus-driven electron acceleration during the 17 March 2013 storm, when the Van Allen Probes observed very rapid electron acceleration up to several MeV within ~12 hours. A clear radial peak in electron phase space density (PSD) observed near L* ~4 indicates that an internal local acceleration process was operating. We construct the global distribution of chorus wave intensity from the low-altitude electron measurements made by multiple Polar Orbiting Environmental Satellites (POES) satellites over a broad region, which is ultimately used to simulate the radiation belt electron dynamics driven by chorus waves. Our simulation results show remarkable agreement in magnitude, timing, energy dependence, and pitch angle distribution with the observed electron PSD near its peak location. However, radial diffusion and other loss processes may be required to explain the differences between the observation and simulation at other locations away from the PSD peak. Our simulation results, together with previous studies, suggest that local acceleration by chorus waves is a robust and ubiquitous process and plays a critical role in accelerating injected seed electrons with convective energies (~100 keV) to highly relativistic energies (several MeV). Li, W.; Thorne, R.; Ma, Q.; Ni, B.; Bortnik, J.; Baker, D.; Spence, H.; Reeves, G.; Kanekal, S.; Green, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Blake, J.; Fennell, J.; Claudepierre, S.; Published by: Journal of Geophysical Research: Space Physics Published on: 06/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.610.1002/2014JA019945 |
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Chorus acceleration of radiation belt relativistic electrons during March 2013 geomagnetic storm The recent launching of Van Allen probes provides an unprecedent opportunity to investigate variations of the radiation belt relativistic electrons. During the 17\textendash19 March 2013 storm, the Van Allen probes simultaneously detected strong chorus waves and substantial increases in fluxes of relativistic (2 - 4.5 MeV) electrons around L = 4.5. Chorus waves occurred within the lower band 0.1\textendash0.5fce (the electron equatorial gyrofrequency), with a peak spectral density \~10-4 nT2/Hz. Correspondingly, relativistic electron fluxes increased by a factor of 102\textendash103 during the recovery phase compared to the main phase levels. By means of a Gaussian fit to the observed chorus spectra, the drift and bounce-averaged diffusion coefficients are calculated and then used to solve a 2-D Fokker-Planck diffusion equation. Numerical simulations demonstrate that the lower-band chorus waves indeed produce such huge enhancements in relativistic electron fluxes within 15 h, fitting well with the observation. Xiao, Fuliang; Yang, Chang; He, Zhaoguo; Su, Zhenpeng; Zhou, Qinghua; He, Yihua; 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: 05/2014 YEAR: 2014 DOI: 10.1002/2014JA019822 |
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Chorus waves play an important role in energetic electron dynamics in the inner magnetosphere. In this work, we present a new hybrid code, DAWN, to simulate the generation of chorus waves. The DAWN code is unique in that it models cold electrons using linearized fluid equations and hot electrons using particle-in-cell techniques. The simplified fluid equations can be solved with robust and simple algorithms. We demonstrate that discrete chorus elements can be generated using the code. Waveforms of the generated element show amplitude modulation or \textquotedblleftsubpackets,\textquotedblright and the frequency sweep rate of the generated element is found to be consistent with that of observed chorus waves. Using the DAWN code, we then investigate the variation of wave intensity (inline image) with respect to linear growth rates on the equatorial plane. Previous observations showed that the change in linear growth rates of whistler waves modulated by external processes such as density modulations is usually small (inline image), while the variation of the wave intensity is large (inline image). Using a chosen set of background plasma parameters, we demonstrate that a small change (inline image) in linear growth rates can lead to significant variation (inline image) of wave intensity only in the transition from the broadband whistler wave generation regime to the chorus wave generation regime. Our results demonstrate the importance of including nonlinear dynamics of chorus generation in understanding the whistler wave intensity modulation process in the inner magnetosphere. Published by: Journal of Geophysical Research: Space Physics Published on: 05/2014 YEAR: 2014 DOI: 10.1002/2014JA019820 chorus excitation; plasma simulation; whistler intensity modulation |
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In situ observations of Pc1 pearl pulsations by the Van Allen Probes We present in situ observations of Pc1 pearl pulsations using the Van Allen Probes. These waves are often observed using ground-based magnetometers, but are rarely observed by orbiting satellites. With the Van Allen Probes, we have seen at least 14 different pearl pulsation events during the first year of operations. These new in situ measurements allow us to identify the wave classification based on local magnetic field conditions. Additionally, by using two spacecraft, we are able to observe temporal changes in the region of observation. The waves appear to be generated at an overall central frequency, as often observed on the ground, and change polarization from left- to right-handedness as they propagate into a region where they are resonant with the crossover frequency (where R- and L-mode waves have the same phase velocity). By combining both in situ and ground-based data, we have found that the region satisfying electromagnetic ion cyclotron wave generation conditions is azimuthally large while radially narrow. The observation of a similar modulation period on the ground as in the magnetosphere contradicts the bouncing wave packet mechanism of generation. Paulson, K.; Smith, C.; Lessard, M.; Engebretson, M.; Torbert, R.; Kletzing, C.; Published by: Geophysical Research Letters Published on: 04/2014 YEAR: 2014 DOI: 10.1002/2013GL059187 |
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Global statistics of the amplitude distributions of hiss, lightning-generated, and other whistler mode waves from terrestrial VLF transmitters have been obtained from the EXOS-D (Akebono) satellite in the Earth\textquoterights plasmasphere and fitted as functions of L and latitude for two geomagnetic activity ranges (Kp<3 and Kp>3). In particular, the present study focuses on the inner zone L∈[1.4,2] where reliable in situ measurements were lacking. Such statistics are critically needed for an accurate assessment of the role and relative dominance of each type of wave in the dynamics of the inner radiation belt. While VLF waves seem to propagate mainly in a ducted mode at L\~1.5\textendash3 for Kp<3, they appear to be substantially unducted during more disturbed periods (Kp>3). Hiss waves are generally the most intense in the inner belt, and lightning-generated and hiss wave intensities increase with geomagnetic activity. Lightning-generated wave amplitudes generally peak within 10\textdegree of the equator in the region L<2 where magnetosonic wave amplitudes are weak for Kp<3. Based on this statistics, simplified models of each wave type are presented. Quasi-linear pitch angle and energy diffusion rates of electrons by the full wave model are then calculated. Corresponding electron lifetimes compare well with decay rates of trapped energetic electrons obtained from Solar Anomalous and Magnetospheric Particle Explorer and other satellites at L∈[1.4,2]. Agapitov, O.; Artemyev, A.; Mourenas, D.; Kasahara, Y.; Krasnoselskikh, V.; Published by: Journal of Geophysical Research: Space Physics Published on: 04/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.410.1002/2014JA019886 Inner radiation belt; Van Allen Probes; Wave-particle interaction |
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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 |
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Space weather forecasting critically depends upon availability of timely and reliable observational data. It is therefore particularly important to understand how existing and newly planned observational assets perform during periods of severe space weather. Extreme space weather creates challenging conditions under which instrumentation and spacecraft may be impeded or in which parameters reach values that are outside the nominal observational range. This paper analyzes existing and upcoming observational capabilities for forecasting, and discusses how the findings may impact space weather research and its transition to operations. A single limitation to the assessment is lack of information provided to us on radiation monitor performance, which caused us not to fully assess (i.e., not assess short term) radiation storm forecasting. The assessment finds that at least two widely spaced coronagraphs including L4 would provide reliability for Earth-bound CMEs. Furthermore, all magnetic field measurements assessed fully meet requirements. However, with current or even with near term new assets in place, in the worst-case scenario there could be a near-complete lack of key near-real-time solar wind plasma data of severe disturbances heading toward and impacting Earth\textquoterights magnetosphere. Models that attempt to simulate the effects of these disturbances in near real time or with archival data require solar wind plasma observations as input. Moreover, the study finds that near-future observational assets will be less capable of advancing the understanding of extreme geomagnetic disturbances at Earth, which might make the resulting space weather models unsuitable for transition to operations. Posner, A.; Hesse, M.; St. Cyr, O.; Published by: Space Weather Published on: 04/2014 YEAR: 2014 DOI: 10.1002/swe.v12.410.1002/2013SW001007 Assessment; Space Hardware; SWx Forecasting; Van Allen Probes |
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The relativistic electrons in the inner radiation belt have received little attention in the past due to sparse measurements and unforgiving contamination from the inner belt protons. The high-quality measurements of the Magnetic Electron Ion Spectrometer instrument onboard Van Allen Probes provide a great opportunity to investigate the dynamics of relativistic electrons in the low L region. In this letter, we report the newly unveiled pitch angle distribution (PAD) of the energetic electrons with minima at 90\textdegree near the magnetic equator in the inner belt and slot region. Such a PAD is persistently present throughout the inner belt and appears in the slot region during storms. One hypothesis for 90\textdegree minimum PADs is that off 90\textdegree electrons are preferentially heated by chorus waves just outside the plasmapause (which can be at very low L during storms) and/or fast magnetosonic waves which exist both inside and outside the plasmasphere. Zhao, H.; Li, X.; Blake, J.; Fennell, J.; Claudepierre, S.; Baker, D.; Jaynes, A.; Malaspina, D.; Kanekal, S.; Published by: Geophysical Research Letters Published on: 04/2014 YEAR: 2014 DOI: 10.1002/2014GL059725 |
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Quantifying the radiation belt seed population in the 17 March 2013 electron acceleration event We present phase space density (PSD) observations using data from the Magnetic Electron Ion Spectrometer instrument on the Van Allen Probes for the 17 March 2013 electron acceleration event. We confirm previous results and quantify how PSD gradients depend on the first adiabatic invariant. We find a systematic difference between the lower-energy electrons ( Boyd, A.; Spence, H.; Claudepierre, S.; Fennell, J.; Blake, J.; Baker, D.; Reeves, G.; Turner, D.; Published by: Geophysical Research Letters Published on: 04/2014 YEAR: 2014 DOI: 10.1002/2014GL059626 |
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RadFET Dosimeters in the Belt: the Van Allen Probes on Day 365 Van Allen Probes A and B, launched more than a year ago (in August 2012), carried 16 p-channel metal-oxide-semiconductor Radiation-sensitive Field Effect Transistors (RadFET)s into an orbit designed by NASA to probe the heart of the trapped-radiation belts. Nearly 350 days of in situ measurements from the Engineering Radiation Monitor (ERM) (1) demonstrated strong variations of dose rates with time, (2) revealed a critical correlation between the ERM RadFET dosimeters and the ERM Faraday cup data on charged particles, and (3) permitted the mapping of the belts by measuring variation with orbit altitude. This paper provides an update on early results given in a NSREC2012 paper along with details and discussion of the RadFET dosimetry data analyzed . Holmes-Siedle, A.G.; Maurer, R.; Peplowski, P.; Published by: IEEE Transactions on Nuclear Science Published on: 04/2014 |
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RadFET Dosimeters in the Belt: the Van Allen Probes on Day 365 Van Allen Probes A and B, launched more than a year ago (in August 2012), carried 16 p-channel metal-oxide-semiconductor Radiation-sensitive Field Effect Transistors (RadFET)s into an orbit designed by NASA to probe the heart of the trapped-radiation belts. Nearly 350 days of in situ measurements from the Engineering Radiation Monitor (ERM) (1) demonstrated strong variations of dose rates with time, (2) revealed a critical correlation between the ERM RadFET dosimeters and the ERM Faraday cup data on charged particles, and (3) permitted the mapping of the belts by measuring variation with orbit altitude. This paper provides an update on early results given in a NSREC2012 paper along with details and discussion of the RadFET dosimetry data analyzed . Holmes-Siedle, A.; Goldsten, J.; Maurer, R.; Peplowski, P.; Published by: IEEE Transactions on Nuclear Science Published on: 04/2014 YEAR: 2014 DOI: 10.1109/TNS.2014.2307012 |
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Simulations from our newly expanded ring current-atmosphere interactions model with self-consistent magnetic field (RAM-SCB), now valid out to 9 RE, are compared for the first time with Van Allen Probes observations. The expanded model reproduces the storm time ring current buildup due to the increased convection and inflow of plasma from the magnetotail. It matches Magnetic Electron Ion Spectrometer (MagEIS) observations of the trapped high-energy (>50 keV) ion flux; however, it underestimates the low-energy (<10 keV) Helium, Oxygen, Proton, and Electron (HOPE) observations. The dispersed injections of ring current ions observed with the Energetic particle, Composition, and Thermal plasma (ECT) suite at high (>20 keV) energy are better reproduced using a high-resolution convection model. In agreement with Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations, RAM-SCB indicates that the large-scale magnetic field is depressed as close as \~4.5 RE during even a moderate storm. Regions of electromagnetic ion cyclotron instability are predicted on the duskside from \~6 to \~9 RE, indicating that previous studies confined to geosynchronous orbit may have underestimated their scattering effect on the energetic particles. Jordanova, V.; Yu, Y.; Niehof, J.; Skoug, R.; Reeves, G.; Kletzing, C.; Fennell, J.; Spence, H.; Published by: Geophysical Research Letters Published on: 04/2014 YEAR: 2014 DOI: 10.1002/2014GL059533 |
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Van Allen Probes observations of direct wave-particle interactions Quasiperiodic increases, or \textquotedblleftbursts,\textquotedblright of 17\textendash26 keV electron fluxes in conjunction with chorus wave bursts were observed following a plasma injection on 13 January 2013. The pitch angle distributions changed during the burst events, evolving from sinN(α) to distributions that formed maxima at α = 75\textendash80\textdegree, while fluxes at 90\textdegree and <60\textdegree remained nearly unchanged. The observations occurred outside of the plasmasphere in the postmidnight region and were observed by both Van Allen Probes. Density, cyclotron frequency, and pitch angle of the peak flux were used to estimate resonant electron energy. The result of ~15\textendash35 keV is consistent with the energies of the electrons showing the flux enhancements and corresponds to electrons in and above the steep flux gradient that signals the presence of an Alfv\ en boundary in the plasma. The cause of the quasiperiodic nature (on the order of a few minutes) of the bursts is not understood at this time. Fennell, J.; Roeder, J.; Kurth, W.; Henderson, M.; Larsen, B.; Hospodarsky, G.; Wygant, J.; Claudepierre, J.; Blake, J.; Spence, H.; Clemmons, J.; Funsten, H.; Kletzing, C.; Reeves, G.; Published by: Geophysical Research Letters Published on: 03/2014 YEAR: 2014 DOI: 10.1002/2013GL059165 |
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Analytic expressions for ULF wave radiation belt radial diffusion coefficients We present analytic expressions for ULF wave-derived radiation belt radial diffusion coefficients, as a function of L and Kp, which can easily be incorporated into global radiation belt transport models. The diffusion coefficients are derived from statistical representations of ULF wave power, electric field power mapped from ground magnetometer data, and compressional magnetic field power from in situ measurements. We show that the overall electric and magnetic diffusion coefficients are to a good approximation both independent of energy. We present example 1-D radial diffusion results from simulations driven by CRRES-observed time-dependent energy spectra at the outer boundary, under the action of radial diffusion driven by the new ULF wave radial diffusion coefficients and with empirical chorus wave loss terms (as a function of energy, Kp and L). There is excellent agreement between the differential flux produced by the 1-D, Kp-driven, radial diffusion model and CRRES observations of differential electron flux at 0.976 MeV\textemdasheven though the model does not include the effects of local internal acceleration sources. Our results highlight not only the importance of correct specification of radial diffusion coefficients for developing accurate models but also show significant promise for belt specification based on relatively simple models driven by solar wind parameters such as solar wind speed or geomagnetic indices such as Kp. Ozeke, Louis; Mann, Ian; Murphy, Kyle; Rae, Jonathan; Milling, David; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2014 YEAR: 2014 DOI: 10.1002/2013JA019204 |
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We expanded our previous work on L* neural networks that used empirical magnetic field models as the underlying models by applying and extending our technique to drift shells calculated from a physics-based magnetic field model. While empirical magnetic field models represent an average, statistical magnetospheric state, the RAM-SCB model, a first-principles magnetically self-consistent code, computes magnetic fields based on fundamental equations of plasma physics. Unlike the previous L* neural networks that include McIlwain L and mirror point magnetic field as part of the inputs, the new L* neural network only requires solar wind conditions and the Dst index, allowing for an easier preparation of input parameters. This new neural network is compared against those previously trained networks and validated by the tracing method in the International Radiation Belt Environment Modeling (IRBEM) library. The accuracy of all L* neural networks with different underlying magnetic field models is evaluated by applying the electron phase space density (PSD)-matching technique derived from the Liouville\textquoterights theorem to the Van Allen Probes observations. Results indicate that the uncertainty in the predicted L* is statistically (75\%) below 0.7 with a median value mostly below 0.2 and the median absolute deviation around 0.15, regardless of the underlying magnetic field model. We found that such an uncertainty in the calculated L* value can shift the peak location of electron phase space density (PSD) profile by 0.2 RE radially but with its shape nearly preserved. Yu, Yiqun; Koller, Josef; Jordanova, Vania; Zaharia, Sorin; Friedel, Reinhard; Morley, Steven; Chen, Yue; Baker, Daniel; Reeves, Geoffrey; Spence, Harlan; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.310.1002/2013JA019350 |
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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 |
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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 |
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Cosmic ray physics in space: from fundamental physics to applications One hundred years after their discovery by Victor Hess, cosmic rays are nowadays subject of intense research from space-based detectors, able to perform for the first time high precision measurement of their composition and spectra as well as of isotropy and time variability. On May 2011, the alpha magnetic spectrometer (AMS-02) has been installed on the International Space Station, to measure with high accuracy the cosmic ray properties searching for rare events which could be an indication of the nature of dark matter or presence of nuclear antimatter. AMS-02 is the result of nearly two decades of effort of an international collaboration, involving in particular Chinese and Italian scientists, to design and build a state of the art detector capable to perform high precision cosmic rays measurement. In this paper, I will briefly report on the first results of AMS-02 as well as about two cosmic rays researches related researches which are spinoffs of the AMS technology development: utilization of superconductivity in space to develop magnetic shields capable to protect the astronauts from the intense dose of radiation collected during an interplanetary mission and study of the lithospheric\textendashmagnetospheric interactions linking seismology to cosmic rays in the context of the Sino-Italian collaboration on the China seismo-electromagnetic satellite. Published by: Rendiconti Lincei Published on: 03/2014 YEAR: 2014 DOI: 10.1007/s12210-014-0293-1 Anti matter; Cosmic rays; Dark matter; Seismology; Space research; Superconductivity; Van Allen Belts |
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Cost and risk analysis of small satellite constellations for earth observation Distributed Space Missions (DSMs) are gaining momentum in their application to Earth science missions owing to their ability to increase observation sampling in spatial, spectral, temporal and angular dimensions. Past literature from academia and industry have proposed and evaluated many cost models for spacecraft as well as methods for quantifying risk. However, there have been few comprehensive studies quantifying the cost for multiple spacecraft, for small satellites and the cost risk for the operations phase of the project which needs to be budgeted for when designing and building efficient architectures. This paper identifies the three critical problems with the applicability of current cost and risk models to distributed small satellite missions and uses data-based modeling to suggest changes that can be made in some of them to improve applicability. Learning curve parameters to make multiple copies of the same unit, technological complexity based costing and COTS enabled small satellite costing have been studied and insights provided. Nag, Sreeja; LeMoigne, Jacqueline; de Weck, Olivier; Published by: Published on: 03/2014 YEAR: 2014 DOI: 10.1109/AERO.2014.6836396 |
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The Johns Hopkins University Applied Physics Laboratory (JHU/APL) is dedicated to solving critical challenges as set forth by the National Aeronautics and Space Administration and the Department of Defense. JHU/APL participates fully in the nation\textquoterights formulation of space science and exploration priorities, providing the needed science, engineering, and technology, including the production and operation of unique spacecraft, instruments, and subsystems. Liggett, William; Handiboe, Jon; Theus, Eugene; Hartka, Ted; Navid, Hadi; Published by: Published on: 03/2014 YEAR: 2014 DOI: 10.1109/AERO.2014.6836273 |
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We study the effect of electromagnetic ion cyclotron (EMIC) waves on the loss and pitch angle scattering of relativistic and ultrarelativistic electrons during the recovery phase of a moderate geomagnetic storm on 11 October 2012. The EMIC wave activity was observed in situ on the Van Allen Probes and conjugately on the ground across the Canadian Array for Real-time Investigations of Magnetic Activity throughout an extended 18 h interval. However, neither enhanced precipitation of >0.7 MeV electrons nor reductions in Van Allen Probe 90\textdegree pitch angle ultrarelativistic electron flux were observed. Computed radiation belt electron pitch angle diffusion rates demonstrate that rapid pitch angle diffusion is confined to low pitch angles and cannot reach 90\textdegree. For the first time, from both observational and modeling perspectives, we show evidence of EMIC waves triggering ultrarelativistic (~2\textendash8 MeV) electron loss but which is confined to pitch angles below around 45\textdegree and not affecting the core distribution. Usanova, M.; Drozdov, A.; Orlova, K.; Mann, I.; Shprits, Y.; Robertson, M.; Turner, D.; Milling, D.; Kale, A.; Baker, D.; Thaller, S.; Reeves, G.; Spence, H.; Kletzing, C.; Wygant, J.; Published by: Geophysical Research Letters Published on: 03/2014 YEAR: 2014 DOI: 10.1002/2013GL059024 |
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Event-specific chorus wave and electron seed population models in DREAM3D using the Van Allen Probes The DREAM3D diffusion model is applied to Van Allen Probes observations of the fast dropout and strong enhancement of MeV electrons during the October 2012 \textquotedblleftdouble-dip\textquotedblright storm. We show that in order to explain the very different behavior in the two \textquotedblleftdips,\textquotedblright diffusion in all three dimensions (energy, pitch angle, and L*) coupled with data-driven, event-specific inputs, and boundary conditions is required. Specifically, we find that outward radial diffusion to the solar wind-driven magnetopause, an event-specific chorus wave model, and a dynamic lower-energy seed population are critical for modeling the dynamics. In contrast, models that include only a subset of processes, use statistical wave amplitudes, or rely on inward radial diffusion of a seed population, perform poorly. The results illustrate the utility of the high resolution, comprehensive set of Van Allen Probes\textquoteright measurements in studying the balance between source and loss in the radiation belt, a principal goal of the mission. Tu, Weichao; Cunningham, G.; Chen, Y.; Morley, S.; Reeves, G.; Blake, J.; Baker, D.; Spence, H.; Published by: Geophysical Research Letters Published on: 03/2014 YEAR: 2014 DOI: 10.1002/2013GL058819 |
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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 |
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Optimization of deep-space Ka-band link schedules Downlink scheduling methods that minimize either contact time or data latency are described. For deep-space missions these two methods yield very different schedules. Optimal scheduling algorithms are straightforward for ideal mission scenarios. In practice, additional schedule requirements preclude a tractable optimal algorithm. In lieu of an optimal solution, an iterative sub-optimal algorithm is described. These methods are motivated in part by a need to balance mission risk, which increases with data latency, and mission cost, which increases with contact time. Cost is reduced by delaying downlink contacts until higher data rates are available. Previous work described optimization of individual Ka-band contacts in the presence of time-varying and statistical link parameters. The present study builds on previous work by using a downlink capacity profile to optimize the downlink schedule over the duration of a mission. The downlink schedule for the NASA mission Solar Probe Plus is used as a case study. Adams, Norman; Copeland, David; Mick, Alan; Pinkine, Nickalaus; Published by: Published on: 03/2014 YEAR: 2014 DOI: 10.1109/AERO.2014.6836351 optimisation; scheduling; space communication links; statistical analysis |
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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 |
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We have recently conducted a statistical survey on pitch angle distributions of energetic electrons trapped in the Earth\textquoterights outer radiation belt, and a new empirical model was developed based upon survey results. This model\textemdashrelativistic electron pitch angle distribution (REPAD)\textemdashaims to present statistical pictures of electron equatorial pitch angle distributions, instead of the absolute flux levels, as a function of energy, L shell, magnetic local time, and magnetic activity. To quantify and facilitate this statistical survey, we use Legendre polynomials to fit long-term in situ directional fluxes observed near the magnetic equator from three missions: CRRES, Polar, and LANL-97A. As the first of this kind of model, REPAD covers the whole outer belt region, providing not only the mean and median pitch angle distributions in the area but also error estimates of the average distributions. Preliminary verification and validation results demonstrate the reliable performance of this model. Usage of REPAD is mainly to predict the full pitch angle distribution of fluxes along a given magnetic field line, or even on a given drift shell, based upon one single unidirectional or omnidirectional flux measurement anywhere on that field line. This can be particularly useful for data assimilation, which usually has large tolerance on data errors. In addition, relatively small variations in pitch angle distributions measured at L shell between ~ 4 and 5 justify the assumption of fixed pitch angle distributions at GPS equatorial crossings (L ~ 4.2) used in our previous studies. Chen, Yue; Friedel, Reiner; Henderson, Michael; Claudepierre, Seth; Morley, Steven; Spence, Harlan; Published by: Journal of Geophysical Research: Space Physics Published on: 03/2014 YEAR: 2014 DOI: 10.1002/jgra.v119.310.1002/2013JA019431 Earth\textquoterights outer radiation belt; energetic electrons; Pitch-angle distributions |
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We have recently conducted a statistical survey on pitch angle distributions of energetic electrons trapped in the Earth\textquoterights outer radiation belt, and a new empirical model was developed based upon survey results. This model\textemdashrelativistic electron pitch angle distribution (REPAD)\textemdashaims to present statistical pictures of electron equatorial pitch angle distributions, instead of the absolute flux levels, as a function of energy, L shell, magnetic local time, and magnetic activity. To quantify and facilitate this statistical survey, we use Legendre polynomials to fit long-term in situ directional fluxes observed near the magnetic equator from three missions: CRRES, Polar, and LANL-97A. As the first of this kind of model, REPAD covers the whole outer belt region, providing not only the mean and median pitch angle distributions in the area but also error estimates of the average distributions. Preliminary verification and validation results demonstrate the reliable performance of this model. Usage of REPAD is mainly to predict the full pitch angle distribution of fluxes along a given magnetic field line, or even on a given drift shell, based upon one single unidirectional or omnidirectional flux measurement anywhere on that field line. This can be particularly useful for data assimilation, which usually has large tolerance on data errors. In addition, relatively small variations in pitch angle distributions measured at L shell between ~ 4 and 5 justify the assumption of fixed pitch angle distributions at GPS equatorial crossings (L ~ 4.2) used in our previous studies. Chen, Y.; Friedel, R.; Henderson, M.; Claudepierre, S.; Morley, S.; Spence, H.; Published by: Journal of Geophysical Research Published on: 03/2014 YEAR: 2014 DOI: 10.1002/2013JA019431 |
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Resonant scattering of energetic electrons by unusual low-frequency hiss We quantify the resonant scattering effects of the unusual low-frequency dawnside plasmaspheric hiss observed on 30 September 2012 by the Van Allen Probes. In contrast to normal (~100\textendash2000 Hz) hiss emissions, this unusual hiss event contained most of its wave power at ~20\textendash200 Hz. Compared to the scattering by normal hiss, the unusual hiss scattering speeds up the loss of ~50\textendash200 keV electrons and produces more pronounced pancake distributions of ~50\textendash100 keV electrons. It is demonstrated that such unusual low-frequency hiss, even with a duration of a couple of hours, plays a particularly important role in the decay and loss process of energetic electrons, resulting in shorter electron lifetimes for ~50\textendash400 keV electrons than normal hiss, and should be carefully incorporated into global modeling of radiation belt electron dynamics during periods of intense injections. Ni, Binbin; Li, Wen; Thorne, Richard; Bortnik, Jacob; Ma, Qianli; Chen, Lunjin; Kletzing, Craig; Kurth, William; Hospodarsky, George; Reeves, Geoffrey; Spence, Harlan; Blake, Bernard; Fennell, Joseph; Claudepierre, Seth; Published by: Geophysical Research Letters Published on: 03/2014 YEAR: 2014 DOI: 10.1002/2014GL059389 |
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A scripting framework for automated flight SW testing: Van Allen Probes lessons learned This paper summarizes the lessons learned from implementing and utilizing an automated flight software test framework for the Van Allen Probes mission. This includes a recommended list of features/characteristics that a test framework should support. This paper also presents two test scripting design patterns that are useful for constructing an automated regression test suite. These design patterns are intended for non-object-oriented scripting environments - which is typical of space mission ground systems. A process flow is described for developing and utilizing an automated test scripting framework for future missions based upon the design patterns presented herein. Published by: Published on: 03/2014 YEAR: 2014 DOI: 10.1109/AERO.2014.6836164 Automated flight software; Automated flight SW testing; Van Allen Probes |
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Signature modeling for LWIR spectrometer Hyperspectral longwave infrared (LWIR) is used for a variety of targets such as gases and solids with the advantage of day or night data collections. A longwave infrared system must have the ability to convert the radiance data it measures to emissivity prior to running a detection algorithm, commonly called a temperature-emissivity separation (TES) algorithm. Key parts of this TES algorithm are accounting for the reflected down-welling radiation from the atmosphere, upwelling background radiance removal, and most importantly determining the temperature of the material. Accounting for these environmental conditions allows for the data to be processed in emissivity to be used in the detection algorithm. The processed data also allows a baseline to determine where key features exist in the signatures collected. In this paper a new method is introduced to process field collected signatures gathered using the Design \& Prototypes microFTIR Model 102. The issue addressed here is calculating the collected signature from radiance to emissivity using a new technique for estimating the surface temperature of the collected sample. The key component of the TES was created to ensure the collected spectra are processed in emissivity space at a quality that is suitable for the detection library on air and ground LWIR systems. Firpi, Alexer; Oxenrider, Jason; Ramachandran, Vignesh; Mitchell, Herbert; Tzeng, Nigel; Rodriguez, Benjamin; Published by: Published on: 03/2014 YEAR: 2014 DOI: 10.1109/AERO.2014.6836439 hyperspectral imaging; infrared imaging; infrared spectrometers; radiance data conversion |
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Software controlled memory scrubbing for the Van Allen Probes Solid State Recorder (SSR) memory The Van Allen Probes mission which was designed and built by the Johns Hopkins University, Applied Physics Laboratory (APL) is also being operated by the APL mission operations team in Laurel, Maryland. The two Van Allen Probes spacecraft have been successfully collecting data on orbit since they were launched on August 30, 2012. These twin probes are providing unprecedented insight into the physical dynamics of the Earth\textquoterights radiation belts and are giving scientists the data they need to make predictions of changes in this critical region of space, by sampling the harsh radiation belt environment where major space weather activity occurs and many spacecraft operate.[1] Shortly after launch, radiation induced anomalies were reported on both spacecraft and investigated by the hardware and software engineering teams. The most significant of these anomalies was associated with single-event effects experienced by the spacecraft Solid State Recorder (SSR) memory. The radiation effects resulted in correctable memory errors but with a secondary effect of data corruption within the SSR. The investigation into these anomalies ultimately identified a subtle hardware design defect, which was reproducible in a controlled ground test environment. This paper details the nature of the memory upsets and hardware mitigation interactions, and the effect these had on the spacecraft science and housekeeping data. It also describes the subsequent investigation and testing to uncover the hardware shortcomings and the implementation and upload of modified flight software to the operational spacecraft. Lastly this paper will provide on-orbit performance data for the SSR since the modified software was made active. Altogether, this will provide insight into not only the challenges of designing for the harsh radiation environment, but also into the need for flexibility when designing systems. Published by: Published on: 03/2014 YEAR: 2014 DOI: 10.1109/AERO.2014.6836406 |
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Space science: Near-Earth space shows its stripes Using some of the first scientific satellites put into orbit during the late 1950s, teams led by physicists James Van Allen in the United States and Sergei Vernov in the Soviet Union independently reported1, 2 on defined regions of radiation in near-Earth space. These regions came to be known as Earth\textquoterights radiation belts, and they represent the first major scientific discovery of the space age. However, despite decades of study, many questions in radiation-belt physics remain unanswered, mostly concerning the nature of the inner and outer belts, which are populated by electrons moving at near the speed of light. As society becomes ever more dependent on satellite-based technology, it is increasingly important to understand the variability in the radiation belts, because the highest-energy \textquotedblleftkiller electrons\textquotedblright3 can result in potentially fatal damage to sensitive spacecraft electronics4. On page 338 of this issue, Ukhorskiy et al.5 present observations and a model of a previously unexplained structured feature of the inner radiation belt, which they call zebra stripes. Published by: Nature Published on: 03/2014 YEAR: 2014 DOI: 10.1038/507308a |
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Spin stabilization design and testing of the Van Allen Probes This paper describes the design decisions taken and the mass properties tracking and testing flow chosen for the Van Allen Probes spacecraft and their deployable systems to achieve the coning angle requirements. Topics include a list of major requirements, a brief description of the error budget, a description of the tracking process of the spacecraft mass properties prior to test, a description of the spin balance and mass properties testing of the spacecraft core and deployable systems, and a presentation of the final mass properties and coning angle calculations of the fully deployed observatories. Launched August 30, 2012, the observed on-orbit, fully deployed configuration coning angles met the requirements, validating the spin balance and mass properties tracking, testing, and calculation methods chosen for the Van Allen Probes mission. Berman, Simmie; Cheng, Weilun; Borowski, Heather; Persons, David; Published by: Published on: 03/2014 YEAR: 2014 DOI: 10.1109/AERO.2014.6836234 |
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Observation and model results accumulated in the last decade indicate that substorms can promptly inject relativistic \textquoteleftkiller\textquoteright electrons (>=MeV) in addition to 10\textendash100 keV subrelativistic populations. Using measurements from Cluster, Polar, LANL, and GOES satellites near the midnight sector, we show in two events that intense electric fields, as large as 20 mV/m, associated with substorm dipolarization are associated with injections of relativistic electrons into the outer radiation belt. Enhancements of hundreds of keV electrons at dipolarization in the magnetotail can account for the injected MeV electrons through earthward transport. These observations provide evidence that substorm electric fields inject relativistic electrons by transporting magnetotail electrons into the outer radiation belt. In these two events, injected relativistic electrons dominated the substorm timescale enhancement of MeV electrons as observed at geosynchronous orbit. Dai, Lei; Wygant, John; Cattell, Cynthia; Thaller, Scott; Kersten, Kris; Breneman, Aaron; Tang, Xiangwei; Friedel, Reiner; Claudepierre, Seth; Tao, Xin; Published by: Geophysical Research Letters Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2014GL059228 radiation belt relativistic electrons; substorm dipolarization; substorm electric fields; substorm injection |
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Substorm injected electrons (several\textendash100 s keV) produce whistler-mode chorus waves that are thought to have a major impact on the radiation belts by causing both energization and loss of relativistic electrons in the outer belt. High-altitude measurements, such as those from the Van Allen Probes, provide detailed wave measurements at a few points in the magnetosphere. But physics-based models of radiation-belt dynamics require knowledge of the global distribution of chorus waves. We demonstrate that time-dependent, global distributions of near-equatorial chorus wave intensities can be inferred from low-Earth-orbit (LEO) measurements of precipitating low-energy electrons. We compare in situ observations of near-equatorial chorus waves with LEO observations of precipitating electrons and derive a heuristic formula that relates, quantitatively, electron precipitation fluxes to chorus wave intensities. Finally, we demonstrate how that formula can be applied to LEO precipitation measurements and in situ Van Allen Probes wave measurements to provide global, data-driven inputs for radiation belt models. Chen, Yue; Reeves, Geoffrey; Friedel, Reiner; Cunningham, Gregory; Published by: Geophysical Research Letters Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2013GL059181 |
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Combining Time History of Events and Macroscale Interaction during Substorms (THEMIS) wave and particle observations and a quantitative calculation of linear wave growth rate, we demonstrate that magnetosonic (MS) waves can be locally excited by ion ring distributions in the Earth\textquoterights magnetosphere when the ion ring energy is comparable to the local Alfven energy. MS waves in association with ion ring distributions were observed by THEMIS A on 24 November 2010 in the afternoon sector, both outside the plasmapause where the wave spectrum varied with fLHR and inside the plasmapause where the wave frequency band remained nearly constant. Our plasma instability analysis in three different regions shows that higher and narrow frequency band MS waves are excited locally outside the plasmapause, and lower and broad frequency band MS waves are excited in the region where the density slightly increases. However, there is no evidence for wave excitation inside the plasmapause, and wave propagation from a distant source is needed to explain their existence. The simulation of the MS wave growth rate spectra during this event agrees reasonably well with the observed wave magnetic field power spectra. We also simulated a MS wave event on 19 October 2011 in the dusk sector and found that the ion ring distribution with an ion ring energy slightly higher than the local Alfven energy can excite the typical broad band MS waves outside the plasmapause. Ma, Qianli; Li, Wen; Chen, Lunjin; Thorne, Richard; Angelopoulos, Vassilis; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2013JA019591 magnetosonic waves; ring current; THEMIS observation; wave excitation |
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Photoelectron-mediated spacecraft potential fluctuations Electric field fluctuations such as those due to plasma waves in Earth\textquoterights magnetosphere may modulate photoelectrons emitted from spacecraft surface, causing fluctuations in spacecraft potential. We experimentally investigate such photoelectron-mediated spacecraft potential fluctuations. The photoelectric charge of a spacecraft model is found to increase with increasing applied electric field as more photoelectrons escape the spacecraft model surface and dissipates with a decrease in the electric field through collection of ambient plasma electrons. When the applied electric field is driven to oscillate at a frequency lower than the response frequency of the spacecraft model, the surface potential follows the electric field oscillations. The spacecraft model maintains an approximately constant potential if the electric field oscillations are driven at a much higher frequency. When a high-frequency electric field modulated by a low-frequency envelope is applied, rectified oscillations in the potential of the spacecraft model are observed. Our experimental results indicate that photoelectron-mediated wave rectifications must be taken into account when spacecraft potential fluctuations are used to infer plasma density structures. Wang, X.; Malaspina, D.; Ergun, R.; M., Hor\; Published by: Journal of Geophysical Research: Space Physics Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2013JA019502 chorus waves; electric field; Magnetosphere; photoelectrons; plasma density; spacecraft potential fluctuations |
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Quantifying hiss-driven energetic electron precipitation: A detailed conjunction event analysis We analyze a conjunction event between the Van Allen Probes and the low-altitude Polar Orbiting Environmental Satellite (POES) to quantify hiss-driven energetic electron precipitation. A physics-based technique based on quasi-linear diffusion theory is used to estimate the ratio of precipitated and trapped electron fluxes (R), which could be measured by the two-directional POES particle detectors, using wave and plasma parameters observed by the Van Allen Probes. The remarkable agreement between modeling and observations suggests that this technique is applicable for quantifying hiss-driven electron scattering near the bounce loss cone. More importantly, R in the 100\textendash300 keV energy channel measured by multiple POES satellites over a broad L magnetic local time region can potentially provide the spatiotemporal evolution of global hiss wave intensity, which is essential in evaluating radiation belt electron dynamics, but cannot be obtained by in situ equatorial satellites alone. Li, W.; Ni, B.; Thorne, R.; Bortnik, J.; Nishimura, Y.; Green, J.; Kletzing, C.; Kurth, W.; Hospodarsky, G.; Spence, H.; Reeves, G.; Blake, J.; Fennell, J.; Claudepierre, S.; Gu, X.; Published by: Geophysical Research Letters Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2013GL059132 |
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He ions contribute to Earth\textquoterights ring current energy and species population density and are important in understanding ion transport and charge exchange processes in the inner magnetosphere. He ion flux measurements made by the Van Allen Probes Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instrument are presented in this paper. Particular focus is centered on geomagnetically quiet intervals in late 2012 and 2013 that show the flux, L-shell, and energy (65 keV to 518 keV) morphology of ring current He ions between geomagnetic storm injection events. The overall He ion abundance during the first nine months of RBSPICE observations, the appearance of a persistent high energy, low L-shell He ion population, and the temporal evolution of this population all provide new insights into trapped ring current energy He ions. These data provide a unique resource that will be used to provide verifications of, and improvements to, models of He ion transport and loss in Earth\textquoterights ring current region. Gerrard, Andrew; Lanzerotti, Louis; Gkioulidou, Matina; Mitchell, Donald; Manweiler, Jerry; Bortnik, Jacob; Published by: Geophysical Research Letters Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2013GL059175 |
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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 |
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We simulate substorm injections observed by the Van Allen Probes during the 17 March 2013 storm using a self-consistent coupling between the ring current model RAM-SCB and the global MHD model BATS-R-US. This is a significant advancement compared to previous studies that used artificially imposed electromagnetic field pulses to mimic substorm dipolarization and associated inductive electric field. Several substorm dipolarizations and injections are reproduced in the MHD model, in agreement with the timing of shape changes in the AE/AL index. The associated inductive electric field transports plasma sheet plasma to geostationary altitudes, providing the boundary plasma source to the ring current model. It is found that impulsive plasma sheet injections, together with a large-scale convection electric field, are necessary to develop a strong ring current. Comparisons with Van Allen Probes observations show that our model reasonably well captures dispersed electron injections and the global Dst index. Yu, Yiqun; Jordanova, Vania; Welling, Dan; Larsen, Brian; Claudepierre, Seth; Kletzing, Craig; Published by: Geophysical Research Letters Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2014GL059322 ring current dynamics; self-consistent treatment of fields and plasma; Substorm Injections; Van Allen Probes |
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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 |
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\textquotedblleftSpacecraft Reveals Recent Geological Activity on the Moon\textquotedblright Through a content analysis of 200 \textquotedbllefttweets,\textquotedblright this study was an exploration into the distinct features of text posted to NASA\textquoterights Twitter site and the potential for these posts to serve as more engaging scientific text than traditional textbooks for adolescents. Results of the content analysis indicated the tweets and linked texts on the NASA Twitter site were constructed primarily as a form of \textquotedblleftadapted primary literature\textquotedblright where science texts created by scientists for other scientists are presented in a slightly modified format for the general public. Further, the content analysis revealed the majority of text posted was designed to cultivate scientific knowledge for novices. Findings of the content analysis are presented and implications for teaching scientific literacies to adolescents using the social media site Twitter are discussed. Published by: Journal of Adolescent \& Adult Literacy Published on: 02/2014 YEAR: 2014 DOI: 10.1002/jaal.2014.57.issue-510.1002/jaal.258 Adolescence; Content analyses; Content literacy; Digital/media literacies |
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Spatial localization and ducting of EMIC waves: Van Allen Probes and ground-based observations On 11 October 2012, during the recovery phase of a moderate geomagnetic storm, an extended interval (> 18 h) of continuous electromagnetic ion cyclotron (EMIC) waves was observed by Canadian Array for Real-time Investigations of Magnetic Activity and Solar-Terrestrial Environment Program induction coil magnetometers in North America. At around 14:15 UT, both Van Allen Probes B and A (65\textdegree magnetic longitude apart) in conjunction with the ground array observed very narrow (ΔL ~ 0.1\textendash0.4) left-hand polarized EMIC emission confined to regions of mass density gradients at the outer edge of the plasmasphere at L ~ 4. EMIC waves were seen with complex polarization patterns on the ground, in good agreement with model results from Woodroffe and Lysak (2012) and consistent with Earth\textquoterights rotation sweeping magnetometer stations across multiple polarization reversals in the fields in the Earth-ionosphere duct. The narrow L-widths explain the relative rarity of space-based EMIC occurrence, ground-based measurements providing better estimates of global EMIC wave occurrence for input into radiation belt dynamical models. Mann, I.; Usanova, M.; Murphy, K.; Robertson, M.; Milling, D.; Kale, A.; Kletzing, C.; Wygant, J.; Thaller, S.; Raita, T.; Published by: Geophysical Research Letters Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2013GL058581 |
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Storm time observations of plasmasphere erosion flux in the magnetosphere and ionosphere Plasmasphere erosion carries cold dense plasma of ionospheric origin in a storm-enhanced density plume extending from dusk toward and through the noontime cusp and dayside magnetopause and back across polar latitudes in a polar tongue of ionization. We examine dusk sector (20 MLT) plasmasphere erosion during the 17 March 2013 storm (Dst ~ -130 nT) using simultaneous, magnetically aligned direct sunward ion flux observations at high altitude by Van Allen Probes RBSP-A (at ~3.0 Re) and at ionospheric heights (~840 km) by DMSP F-18. Plasma erosion occurs at both high and low altitudes where the subauroral polarization stream flow overlaps the outer plasmasphere. At ~20 UT, RBSP-A observed ~1.2E12 m-2 s-1 erosion flux, while DMSP F-18 observed ~2E13 m-2 s-1 sunward flux. We find close similarities at high and low altitudes between the erosion plume in both invariant latitude spatial extent and plasma characteristics. Foster, J.; Erickson, P.; Coster, A.; Thaller, S.; Tao, J.; Wygant, J.; Bonnell, J; Published by: Geophysical Research Letters Published on: 02/2014 YEAR: 2014 DOI: 10.1002/2013GL059124 |