In addition to clarifying morphological structures of the Earth's radiation belts, it has also been a major achievement of the Van Allen Probes mission to understand more thoroughly how highly ...relativistic and ultrarelativistic electrons are accelerated deep inside the radiation belts. Prior studies have demonstrated that electrons up to energies of 10 megaelectron volts (MeV) can be produced over broad regions of the outer Van Allen zone on timescales of minutes to a few hours. It often is seen that geomagnetic activity driven by strong solar storms (i.e., coronal mass ejections, or CMEs) almost inexorably leads to relativistic electron production through the intermediary step of intense magnetospheric substorms. In this study, we report observations over the 6‐year period 1 September 2012 to 1 September 2018. We focus on data about the relativistic and ultrarelativistic electrons (E≥5 MeV) measured by the Relativistic Electron‐Proton Telescope sensors on board the Van Allen Probes spacecraft. This work portrays the radiation belt acceleration, transport, and loss characteristics over a wide range of geomagnetic events. We emphasize features seen repeatedly in the data (three‐belt structures, “impenetrable” barrier properties, and radial diffusion signatures) in the context of acceleration and loss mechanisms. We especially highlight solar wind forcing of the ultrarelativistic electron populations and extended periods when such electrons were absent. The analysis includes new display tools showing spatial features of the mission‐long time variability of the outer Van Allen belt emphasizing the remarkable dynamics of the system.
Key Points
Essential factors are plentiful substorm “seed particles” and high‐speed (V > 500 km/s) solar wind forcing
The entire relativistic electron population can be wiped out in a few hours by shock wave impact but can rapidly be replenished
Very long intervals have been observed without multimegaelectron volt electrons in the outer belt due to low solar wind driving
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The first in situ measurements of electric and magnetic fields in the near‐Sun environment (< 0.25 AU from the Sun) will be made by the FIELDS instrument suite on the Solar Probe Plus mission. The ...Digital Fields Board (DFB) is an electronics board within FIELDS that performs analog and digital signal processing, as well as digitization, for signals between DC and 60 kHz from five voltage sensors and four search coil magnetometer channels. These nine input signals are processed on the DFB into 26 analog data streams. A specialized application‐specific integrated circuit performs analog to digital conversion on all 26 analog channels simultaneously. The DFB then processes the digital data using a field programmable gate array (FPGA), generating a variety of data products, including digitally filtered continuous waveforms, high‐rate burst capture waveforms, power spectra, cross spectra, band‐pass filter data, and several ancillary products. While the data products are optimized for encounter‐based mission operations, they are also highly configurable, a key design aspect for a mission of exploration. This paper describes the analog and digital signal processing used to ensure that the DFB produces high‐quality science data, using minimal resources, in the challenging near‐Sun environment.
Key Points
The DFB provides analog and digital processing for the FIELDS instrument on Solar Probe Plus
The DFB produces a range of time‐ and spectral‐domain data products
The DFB is optimized for a near‐Sun mission of discovery
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
While the recent Van Allen Probes mission has provided a wealth of trapped particle measurements, questions still arise from analysis of their data. In particular, 10–100s of keV electrons exhibit ...dynamics not well understood with current data. Injections of 33–80 keV electrons can occur during both storm and quiet times as shown by Van Allen Probes data. However, due to the Probes' orbit, they can not distinguish precipitation during these events, necessary to quantify injection rates. Analysis of a Low Earth Orbit (LEO) mission measuring these electron populations found enhancements not explained with current injection sources. Future measurements including the quasi‐trapped and precipitating populations are necessary to resolve these dynamics. We present the Medium Energy Electron Telescope to resolve these uncertainties surrounding 10–100s of keV electrons in the inner belt. This solid‐state particle telescope is optimized for these measurements in the high‐flux inner belt environment, with flight heritage from prior instruments. However, novel instrument design is required to measure these populations at fine energy resolution and fit the instrument into a 1U volume, including that of the detectors, electronics, instrument housing, and collimator components. The design is guided by Geant4 analysis and consideration for expected fluxes using the AE9 and AP9 models for a LEO mission and associated tradeoffs are discussed. We develop 59 energy channels with fine nominal resolution (<20%) for 30–800 keV electrons and show proton measurement capabilities for 1.1–>60 MeV populations. Instrument saturation and proton contamination are quantified by analysis of the instrument's response.
Key Points
Medium Energy Electron Telescope is a solid‐state particle telescope designed to measure 30–800 keV electrons with fine energy resolution, and 1.1–>60 MeV protons
Geant4‐guided instrument design includes consideration for collimator geometry, material, teeth, and the expected flux environment
Count rates are quantified for proving viability of science measurements, including proton contamination effects and instrument saturation
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The Relativistic Electron-Proton Telescope (REPT) instruments were designed to measure ∼2 to >18 MeV electrons and ∼18 to > 115 MeV protons as part of the science payloads onboard the dual Radiation ...Belt Storm Probes (RBSP) spacecraft. The REPT instruments were turned on and configured in their science acquisition modes about 2 days after the RBSP launch on 30 August 2012. The REPT-A and REPT-B instruments both operated flawlessly until mission cessation in 2019. This paper reviews briefly the REPT instrument designs, their operational performance, relevant mode changes and trending over the course of the mission, as well as pertinent background effects (and recommended corrections). A substantial part of this paper highlights discoveries and significant advancement of our understanding of physical-processes obtained using REPT data. We do this for energetic electrons primarily in the outer Van Allen belt and for energetic protons in the inner Van Allen zone. The review also describes several ways in which REPT data were employed for important space weather applications. The paper concludes with assessments of ways that REPT data might further be exploited to continue to advance radiation belt studies. The paper also discusses the pressing and critical need for the operational continuation of REPT-like measurements both for science and for space situational awareness.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The Van Allen Probes mission operations materialized through a distributed model in which operational responsibility was divided between the Mission Operations Center (MOC) and separate instrument ...specific SOCs. The sole MOC handled all aspects of telemetering and receiving tasks as well as certain scientifically relevant ancillary tasks. Each instrument science team developed individual instrument specific SOCs proficient in unique capabilities in support of science data acquisition, data processing, instrument performance, and tools for the instrument team scientists. In parallel activities, project scientists took on the task of providing a significant modeling tool base usable by the instrument science teams and the larger scientific community. With a mission as complex as Van Allen Probes, scientific inquiry occurred due to constant and significant collaboration between the SOCs and in concert with the project science team. Planned cross-instrument coordinated observations resulted in critical discoveries during the seven-year mission. Instrument cross-calibration activities elucidated a more seamless set of data products. Specific topics include post-launch changes and enhancements to the SOCs, discussion of coordination activities between the SOCs, SOC specific analysis software, modeling software provided by the Van Allen Probes project, and a section on lessons learned. One of the most significant lessons learned was the importance of the original decision to implement individual team SOCs providing timely and well-documented instrument data for the NASA Van Allen Probes Mission scientists and the larger magnetospheric and radiation belt scientific community.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
6.
The constitution, progressivism and reform Hoxie, R Gordon; Whitehead, John C; Green, Marshall ...
Presidential studies quarterly,
07/1990, Volume:
XX, Issue:
3
Journal Article
Peer reviewed
Full text
Available for:
BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NMLJ, NUK, ODKLJ, OILJ, PNG, PRFLJ, SAZU, SBCE, SBMB, UL, UM, UPUK
PDF
