The Radiation Belt Storm Probes (RBSP)-Energetic Particle, Composition, and Thermal Plasma (ECT) suite contains an innovative complement of particle instruments to ensure the highest quality ...measurements ever made in the inner magnetosphere and radiation belts. The coordinated RBSP-ECT particle measurements, analyzed in combination with fields and waves observations and state-of-the-art theory and modeling, are necessary for understanding the acceleration, global distribution, and variability of radiation belt electrons and ions, key science objectives of NASA’s Living With a Star program and the Van Allen Probes mission. The RBSP-ECT suite consists of three highly-coordinated instruments: the Magnetic Electron Ion Spectrometer (MagEIS), the Helium Oxygen Proton Electron (HOPE) sensor, and the Relativistic Electron Proton Telescope (REPT). Collectively they cover, continuously, the full electron and ion spectra from one eV to 10’s of MeV with sufficient energy resolution, pitch angle coverage and resolution, and with composition measurements in the critical energy range up to 50 keV and also from a few to 50 MeV/nucleon. All three instruments are based on measurement techniques proven in the radiation belts. The instruments use those proven techniques along with innovative new designs, optimized for operation in the most extreme conditions in order to provide unambiguous separation of ions and electrons and clean energy responses even in the presence of extreme penetrating background environments. The design, fabrication and operation of ECT spaceflight instrumentation in the harsh radiation belt environment ensure that particle measurements have the fidelity needed for closure in answering key mission science questions. ECT instrument details are provided in companion papers in this same issue.
In this paper, we describe the science objectives of the RBSP-ECT instrument suite on the Van Allen Probe spacecraft within the context of the overall mission objectives, indicate how the characteristics of the instruments satisfy the requirements to achieve these objectives, provide information about science data collection and dissemination, and conclude with a description of some early mission results.
The HOPE mass spectrometer of the Radiation Belt Storm Probes (RBSP) mission (renamed the Van Allen Probes) is designed to measure the
in situ
plasma ion and electron fluxes over 4
π
sr at each RBSP ...spacecraft within the terrestrial radiation belts. The scientific goal is to understand the underlying physical processes that govern the radiation belt structure and dynamics. Spectral measurements for both ions and electrons are acquired over 1 eV to 50 keV in 36 log-spaced steps at an energy resolution Δ
E
FWHM
/
E
≈15 %. The dominant ion species (H
+
, He
+
, and O
+
) of the magnetosphere are identified using foil-based time-of-flight (TOF) mass spectrometry with channel electron multiplier (CEM) detectors. Angular measurements are derived using five polar pixels coplanar with the spacecraft spin axis, and up to 16 azimuthal bins are acquired for each polar pixel over time as the spacecraft spins. Ion and electron measurements are acquired on alternate spacecraft spins. HOPE incorporates several new methods to minimize and monitor the background induced by penetrating particles in the harsh environment of the radiation belts. The absolute efficiencies of detection are continuously monitored, enabling precise, quantitative measurements of electron and ion fluxes and ion species abundances throughout the mission. We describe the engineering approaches for plasma measurements in the radiation belts and present summaries of HOPE measurement strategy and performance.
Observations of solar wind from both large polar coronal holes (PCHs) during Ulysses' third orbit showed that the fast solar wind was slightly slower, significantly less dense, cooler, and had less ...mass and momentum flux than during the previous solar minimum (first) orbit. In addition, while much more variable, measurements in the slower, in‐ecliptic wind match quantitatively with Ulysses and show essentially identical trends. Thus, these combined observations indicate significant, long‐term variations in solar wind output from the entire Sun. The significant, long‐term trend to lower dynamic pressures means that the heliosphere has been shrinking and the heliopause must be moving inward toward the Voyager spacecraft. In addition, our observations suggest a significant and global reduction in the mass and energy fed in below the sonic point in the corona. The lower supply of mass and energy may result naturally from a reduction of open magnetic flux during this period.
The last solar minimum, which extended into 2009, was especially deep and prolonged. Since then, sunspot activity has gone through a very small peak while the heliospheric current sheet achieved ...large tilt angles similar to prior solar maxima. The solar wind fluid properties and interplanetary magnetic field (IMF) have declined through the prolonged solar minimum and continued to be low through the current mini solar maximum. Compared to values typically observed from the mid-1970s through the mid-1990s, the following proton parameters are lower on average from 2009 through day 79 of 2013: solar wind speed and beta (~11%), temperature (~40%), thermal pressure (~55%), mass flux (~34%), momentum flux or dynamic pressure (~41%), energy flux (~48%), IMF magnitude (~31%), and radial component of the IMF (~38%). These results have important implications for the solar wind's interaction with planetary magnetospheres and the heliosphere's interaction with the local interstellar medium, with the proton dynamic pressure remaining near the lowest values observed in the space age: ~1.4 nPa, compared to ~2.4 nPa typically observed from the mid-1970s through the mid-1990s. The combination of lower magnetic flux emergence from the Sun (carried out in the solar wind as the IMF) and associated low power in the solar wind points to the causal relationship between them. Our results indicate that the low solar wind output is driven by an internal trend in the Sun that is longer than the ~11 yr solar cycle, and they suggest that this current weak solar maximum is driven by the same trend.
At suprathermal energies, interplanetary electrons commonly exhibit a magnetic field‐aligned beam referred to as the strahl. The finite strahl width is a consequence of competition between magnetic ...focusing as the interplanetary field weakens with distance from the Sun, and particle scattering acting to broaden the strahl along its propagation path. We present a statistical survey of the strahl using ACE Solar Wind Electron, Proton, and Alpha Monitor (SWEPAM) measurements from 1998 to 2002. A systematic fitting algorithm was applied to pitch angle distributions to identify unidirectional or counterstreaming strahl features and to quantify beam widths and intensities. The analysis indicated that a strahl is present ≥75% of the time, while counterstreaming strahls were observed about 10% of the time. The strahl width ranges from 5° to 90°; importantly, the strahl cannot be characterized by any typical width. Within counterstreaming intervals the strahl peak intensity anticorrelates with beam width while the integrated fluxes of the two simultaneously observed strahls are similar, within a factor of 2 for 75% of counterstreaming periods. Observations are consistent with a model in which integrated strahl flux leaving the corona varies over a limited range, but the degree of beam scattering along the propagation path to 1 AU varies widely. The difference between two concurrent counterstreaming strahls is likely due to different scattering profiles along the different legs of a closed field line loop, both rooted in similar coronal regions. Narrow strahls (<20°) are strongly associated with counterstreaming intervals, as well as high‐speed streams. Strahl width can either increase or decrease with energy.
Key Points
Strahl varies widely and cannot be characterized by any typical width
Strahl peak intensity anticorrelates with the beam width
Very narrow strahls are associated with counterstreaming intervals
Enabled by the comprehensive measurements from the Magnetic Electron Ion Spectrometer (MagEIS), Helium Oxygen Proton Electron mass spectrometer (HOPE), and Radiation Belt Storm Probes Ion Composition ...Experiment (RBSPICE) instruments onboard Van Allen Probes in the heart of the radiation belt, the relative contributions of ions with different energies and species to the ring current energy density and their dependence on the phases of geomagnetic storms are quantified. The results show that lower energy (<50 keV) protons enhance much more often and also decay much faster than higher‐energy protons. During the storm main phase, ions with energies <50 keV contribute more significantly to the ring current than those with higher energies; while the higher‐energy protons dominate during the recovery phase and quiet times. The enhancements of higher‐energy proton fluxes as well as energy content generally occur later than those of lower energy protons, which could be due to the inward radial diffusion. For the 29 March 2013 storm we investigated in detail that the contribution from O+ is ~25% of the ring current energy content during the main phase and the majority of that comes from <50 keV O+. This indicates that even during moderate geomagnetic storms the ionosphere is still an important contributor to the ring current ions. Using the Dessler‐Parker‐Sckopke relation, the contributions of ring current particles to the magnetic field depression during this geomagnetic storm are also calculated. The results show that the measured ring current ions contribute about half of the Dst depression.
Key Points
<50 keV ions contribute more to the ring current than those of higher energies at storm main phase
Flux increase of >50 keV protons usually occurs at recovery phase (could be due to radial diffusion)
Even during moderate storms <50 keV O+ still contributes significantly to the ring current energy
The source of O+ in the storm time ring current Kistler, L. M.; Mouikis, C. G.; Spence, H. E. ...
Journal of geophysical research. Space physics,
June 2016, 2016-06-00, 20160601, Letnik:
121, Številka:
6
Journal Article
Recenzirano
Odprti dostop
A stretched and compressed geomagnetic field occurred during the main phase of a geomagnetic storm on 1 June 2013. During the storm the Van Allen Probes spacecraft made measurements of the plasma ...sheet boundary layer and observed large fluxes of O+ ions streaming up the field line from the nightside auroral region. Prior to the storm main phase there was an increase in the hot (>1 keV) and more isotropic O+ ions in the plasma sheet. In the spacecraft inbound pass through the ring current region during the storm main phase, the H+ and O+ ions were significantly enhanced. We show that this enhanced inner magnetosphere ring current population is due to the inward adiabatic convection of the plasma sheet ion population. The energy range of the O+ ion plasma sheet that impacts the ring current most is found to be from ~5 to 60 keV. This is in the energy range of the hot population that increased prior to the start of the storm main phase, and the ion fluxes in this energy range only increase slightly during the extended outflow time interval. Thus, the auroral outflow does not have a significant impact on the ring current during the main phase. The auroral outflow is transported to the inner magnetosphere but does not reach high enough energies to affect the energy density. We conclude that the more energetic O+ that entered the plasma sheet prior to the main phase and that dominates the ring current is likely from the cusp.
Key Points
Auroral outflow during the storm main phase mainly impacts <1 keV plasma sheet population
The >1 keV (hot) more isotropic plasma sheet O+ population increases prior to the main phase
Inward transport of the hot O+ dominates the ring current; this O+ is likely from the cusp
We have obtained direct evidence for local magnetic reconnection in the solar wind using solar wind plasma and magnetic field data obtained by the Advanced Composition Explorer (ACE). The prime ...evidence consists of accelerated ion flow observed within magnetic field reversal regions in the solar wind. Here we report such observations obtained in the interior of an interplanetary coronal mass ejection (ICME) or at the interface between two ICMEs on 23 November 1997 at a time when the magnetic field was stronger than usual. The observed plasma acceleration was consistent with the Walen relationship, which relates changes in flow velocity to density‐weighted changes in the magnetic field vector. Pairs of proton beams having comparable densities and counterstreaming relative to one another along the magnetic field at a speed of ∼1.4VA, where VA was the local Alfven speed, were observed near the center of the accelerated flow event. We infer from the observations that quasi‐stationary reconnection occurred sunward of the spacecraft and that the accelerated flow occurred within a Petschek‐type reconnection exhaust region bounded by Alfven waves and having a cross section width of ∼4 × 105 km as it swept over ACE. The counterstreaming ion beams resulted from solar wind plasma entering the exhaust region from opposite directions along the reconnected magnetic field lines. We have identified a limited number (five) of other accelerated flow events in the ACE data that are remarkably similar to the 23 November 1997 event. All such events identified occurred at thin current sheets associated with moderate to large changes in magnetic field orientation (98°–162°) in plasmas characterized by low proton beta (0.01–0.15) and high Alfven speed (51–204 km/s). They also were all associated with ICMEs.
On 17 March 2013, the Van Allen Probes measured the H+ and O+ fluxes of the ring current during a large geomagnetic storm. Detailed examination of the pressure buildup during the storm shows large ...differences in the pressure measured by the two spacecraft, with measurements separated by only an hour, and large differences in the pressure measured at different local times. In addition, while the H+ and O+ pressure contributions are about equal during the main phase in the near‐Earth plasma sheet outside L = 5.5, the O+ pressure dominates at lower L values. We test whether adiabatic convective transport from the near‐Earth plasma sheet (L > 5.5) to the inner magnetosphere can explain these observations by comparing the observed inner magnetospheric distributions with the source distribution at constant magnetic moment, mu. We find that adiabatic convection can account for the enhanced pressure observed during the storm. Using a Weimer 1996 electric field we model the drift trajectories to show that the key features can be explained by variation in the near‐Earth plasma sheet population and particle access that changes with energy and L shell. Finally, we show that the dominance of O+ at low L shells is due partly to a near‐Earth plasma sheet that is preferentially enhanced in O+ at lower energies (5–10 keV) and partly due to the time dependence in the source combined with longer drift times to low L shells. No source of O+ inside L = 5.5 is required to explain the observations at low L shells.
Key Points
Adiabatic inward convection of the near‐Earth plasma sheet causes the ring current pressure enhancements
Pressure enhancements are dominated by the highest energies able to convect to low L shells
O+ rich source during main phase causes O+ dominance in lower L shells
RBSP‐ECT Combined Spin‐Averaged Electron Flux Data Product Boyd, A. J.; Reeves, G. D.; Spence, H. E. ...
Journal of geophysical research. Space physics,
November 2019, 2019-Nov, 2019-11-00, 20191101, Letnik:
124, Številka:
11
Journal Article
Recenzirano
Odprti dostop
We describe a new data product combining the spin‐averaged electron flux measurements from the Radiation Belt Storm Probes (RBSP) Energetic Particle Composition and Thermal Plasma (ECT) suite on the ...National Aeronautics and Space Administration's Van Allen Probes. We describe the methodology used to combine each of the data sets and produce a consistent set of spectra for September 2013 to the present. Three‐minute‐averaged flux spectra are provided spanning energies from 15 eV up to 20 MeV. This new data product provides additional utility to the ECT data and offers a consistent cross calibrated data set for researchers interested in examining the dynamics of the inner magnetosphere across a wide range of energies.
Key Points
A new combined electron flux data product for the Van Allen Probes mission is described
Results from cross calibration of the RBSP‐ECT instrument suite are presented
This data product represents the first ever complete electron spectra throughout the inner magnetosphere from tens of electron volts to tens of megaelectron volts
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