Journal Article•
The Electric Field and Waves Instruments on the Radiation Belt Storm Probes Mission
TL;DR: In this paper, the Van Allen Probes were used to measure three dimensional quasi-static and low frequency electric fields and waves associated with the acceleration of energetic charged particles in the inner magnetosphere of the Earth.
Abstract: The Electric Fields and Waves (EFW) Instruments on the two Radiation Belt Storm Probe (RBSP) spacecraft (recently renamed the Van Allen Probes) are designed to measure three dimensional quasi-static and low frequency electric fields and waves associated with the major mechanisms responsible for the acceleration of energetic charged particles in the inner magnetosphere of the Earth. For this measurement, the instrument uses two pairs of spherical double probe sensors at the ends of orthogonal centripetally deployed booms in the spin plane with tip-to-tip separations of 100 meters. The third component of the electric field is measured by two spherical sensors separated by ∼15 m, deployed at the ends of two stacer booms oppositely directed along the spin axis of the spacecraft. The instrument provides a continuous stream of measurements over the entire orbit of the low frequency electric field vector at 32 samples/s in a survey mode. This survey mode also includes measurements of spacecraft potential to provide information on thermal electron plasma variations and structure. Survey mode spectral information allows the continuous evaluation of the peak value and spectral power in electric, magnetic and density fluctuations from several Hz to 6.5 kHz. On-board cross-spectral data allows the calculation of field-aligned wave Poynting flux along the magnetic field. For higher frequency waveform information, two different programmable burst memories are used with nominal sampling rates of 512 samples/s and 16 k samples/s. The EFW burst modes provide targeted measurements over brief time intervals of 3-d electric fields, 3-d wave magnetic fields (from the EMFISIS magnetic search coil sensors), and spacecraft potential. In the burst modes all six sensor-spacecraft potential measurements are telemetered enabling interferometric timing of small-scale plasma structures. In the first burst mode, the instrument stores all or a substantial fraction of the high frequency measurements in a 32 gigabyte burst memory. The sub-intervals to be downloaded are uplinked by ground command after inspection of instrument survey data and other information available on the ground. The second burst mode involves autonomous storing and playback of data controlled by flight software algorithms, which assess the “highest quality” events on the basis of instrument measurements and information from other instruments available on orbit. The EFW instrument provides 3-d wave electric field signals with a frequency response up to 400 kHz to the EMFISIS instrument for analysis and telemetry (Kletzing et al. Space Sci. Rev. 2013).
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University of California1, University of Minnesota2, Centre national de la recherche scientifique3, University of Colorado Boulder4, Goddard Space Flight Center5, Swedish Institute of Space Physics6, Queen Mary University of London7, University of New Hampshire8, Imperial College London9, University of Maryland, College Park10, Johns Hopkins University Applied Physics Laboratory11, United States Naval Research Laboratory12, University of Michigan13, Southwest Research Institute14, University of Chicago15, Praxis16, University of California, Los Angeles17
TL;DR: The scientific objectives targeted by the SPP/FIELDS instrument, the instrument design itself, and the instrument concept of operations and planned data products are described.
Abstract: NASA’s Solar Probe Plus (SPP) mission will make the first in situ measurements of the solar corona and the birthplace of the solar wind. The FIELDS instrument suite on SPP will make direct measurements of electric and magnetic fields, the properties of in situ plasma waves, electron density and temperature profiles, and interplanetary radio emissions, amongst other things. Here, we describe the scientific objectives targeted by the SPP/FIELDS instrument, the instrument design itself, and the instrument concept of operations and planned data products.
540 citations
TL;DR: The expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum are described and described.
Abstract: The twin Van Allen Probe spacecraft, launched in August 2012, carry identical scientific payloads. The Electric and Magnetic Field Instrument Suite and Integrated Science suite includes a plasma wave instrument (Waves) that measures three magnetic and three electric components of plasma waves in the frequency range of 10 Hz to 12 kHz using triaxial search coils and the Electric Fields and Waves triaxial electric field sensors. The Waves instrument also measures a single electric field component of waves in the frequency range of 10 to 500 kHz. A primary objective of the higher-frequency measurements is the determination of the electron density ne at the spacecraft, primarily inferred from the upper hybrid resonance frequency fuh. Considerable work has gone into developing a process and tools for identifying and digitizing the upper hybrid resonance frequency in order to infer the electron density as an essential parameter for interpreting not only the plasma wave data from the mission but also as input to various magnetospheric models. Good progress has been made in developing algorithms to identify fuh and create a data set of electron densities. However, it is often difficult to interpret the plasma wave spectra during active times to identify fuh and accurately determine ne. In some cases, there is no clear signature of the upper hybrid band, and the low-frequency cutoff of the continuum radiation is used. We describe the expected accuracy of ne and issues in the interpretation of the electrostatic wave spectrum.
428 citations
University of Alberta1, Moscow State University2, University of California, Los Angeles3, Massachusetts Institute of Technology4, Skolkovo Institute of Science and Technology5, University of Colorado Boulder6, University of Minnesota7, Los Alamos National Laboratory8, University of New Hampshire9, University of Iowa10
TL;DR: In this paper, 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 was studied.
Abstract: 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 >07 MeV electrons nor reductions in Van Allen Probe 90° 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° For the first time, from both observational and modeling perspectives, we show evidence of EMIC waves triggering ultrarelativistic (~2–8 MeV) electron loss but which is confined to pitch angles below around 45° and not affecting the core distribution
313 citations
147 citations
TL;DR: Simulation results show that combined acceleration by chorus and magnetosonic waves can successfully explain the electron flux evolution both in the energy and butterfly pitch angle distribution and provides a great support for the mechanism of wave-driven butterfly distribution of relativistic electrons.
Abstract: Van Allen radiation belts consist of relativistic electrons trapped by Earth's magnetic field. Trapped electrons often drift azimuthally around Earth and display a butterfly pitch angle distribution of a minimum at 90° further out than geostationary orbit. This is usually attributed to drift shell splitting resulting from day-night asymmetry in Earth's magnetic field. However, direct observation of a butterfly distribution well inside of geostationary orbit and the origin of this phenomenon have not been provided so far. Here we report high-resolution observation that a unusual butterfly pitch angle distribution of relativistic electrons occurred within 5 Earth radii during the 28 June 2013 geomagnetic storm. Simulation results show that combined acceleration by chorus and magnetosonic waves can successfully explain the electron flux evolution both in the energy and butterfly pitch angle distribution. The current provides a great support for the mechanism of wave-driven butterfly distribution of relativistic electrons.
144 citations
References
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TL;DR: The Electric and Magnetic Field Instrument and Integrated Science (EMFISIS) investigation on the NASA Radiation Belt Storm Probes (now named the Van Allen Probes) mission provides key wave and very low frequency magnetic field measurements to understand radiation belt acceleration, loss, and transport.
Abstract: The Electric and Magnetic Field Instrument and Integrated Science (EMFISIS) investigation on the NASA Radiation Belt Storm Probes (now named the Van Allen Probes) mission provides key wave and very low frequency magnetic field measurements to understand radiation belt acceleration, loss, and transport. The key science objectives and the contribution that EMFISIS makes to providing measurements as well as theory and modeling are described. The key components of the instruments suite, both electronics and sensors, including key functional parameters, calibration, and performance, demonstrate that EMFISIS provides the needed measurements for the science of the RBSP mission. The EMFISIS operational modes and data products, along with online availability and data tools provide the radiation belt science community with one the most complete sets of data ever collected.
1,060 citations
TL;DR: In this paper, the minimum electron energy for cyclotron resonant interaction with various electromagnetic waves was calculated for conditions representative of storm-times, and the possibility of electron stochastic energization to relativisitic energies (≥ 1 MeV) via resonant waveparticle interactions during a magnetic storm was explored.
Abstract: The possibility of electron stochastic energization to relativisitic energies (≥ 1 MeV) via resonant wave-particle interactions during a magnetic storm is explored. The minimum electron energy Emin for cyclotron resonant interaction with various electromagnetic waves is calculated for conditions representative of storm-times. Since Emin > 1 MeV for resonance with L-mode ion cyclotron waves, intense stormtime EMIC waves could contribute to relativistic electron loss, but not acceleration. Inside the plasmapause whistler mode waves, and highly oblique magnetosonic waves near the lower hybrid frequency, can resonate with electrons over the important energy range from ∼ 100 keV to ∼ 1 MeV. In low density regions outside the plasmapause, the whistler, RX, LO and Z modes can resonate with electrons over a similar energy range. These waves have the potential to contribute to the stochastic acceleration of electrons up to relativistic energies during magnetic storms.
574 citations
TL;DR: The three-axis electric field instrument (EFI) for the NASA THEMIS mission is described in this article, where the authors describe the design, performance, and on-orbit operation of the EFI.
Abstract: The design, performance, and on-orbit operation of the three-axis electric field instrument (EFI) for the NASA THEMIS mission is described. The 20 radial wire boom and 10 axial stacer boom antenna systems making up the EFI sensors on the five THEMIS spacecraft, along with their supporting electronics have been deployed and are operating successfully on-orbit without any mechanical or electrical failures since early 2007. The EFI provides for waveform and spectral three-axis measurements of the ambient electric field from DC up to 8 kHz, with a single, integral broadband channel extending up to 400 kHz. Individual sensor potentials are also measured, providing for on-board and ground-based estimation of spacecraft floating potential and high-resolution plasma density measurements. Individual antenna baselines are 50- and 40-m in the spin plane, and 6.9-m along the spin axis.
480 citations
TL;DR: In this paper, the authors modeled the formation of a new electron radiation belt at about or = 25 that resulted from the Storm Sudden Commencement (SSC) of March 24, 1991 as observed by the Combined Release and Radiation Effects Satellite (CRRES) satellite.
Abstract: We model the rapid (about 1 min) formation of a new electron radiation belt at L about or = 25 that resulted from the Storm Sudden Commencement (SSC) of March 24, 1991 as observed by the Combined Release and Radiation Effects Satellite (CRRES) satellite Guided by the observed electric and magnetic fields, we represent the time-dependent magnetospheric electric field during the SSC by an asymmetric bipolar pulse that is associated with the compression and relaxation of the Earth's magnetic field We follow the electrons using a relativistic guiding center code The test-particle simulations show that electrons with energies of a few MeV at L greater than 6 were energized up to 40 MeV and transported to L about or = 25 during a fraction of their drift period The energization process conserves the first adiabatic invariant and is enhanced due to resonance of the electron drift motion with the time-varying electric field Our simulation results, with an initial W(exp -8) energy flux spectra, reproduce the observed electron drift echoes and show that the interplanetary shock impacted the magnetosphere between 1500 and 1800 MLT
407 citations
TL;DR: In this article, a sine-wave parametric model with a variable amplitude was used to analyze the lower band of chorus below one half of the electron cyclotron frequency, measured at a radial distance of 4.4 Earth's radii, within a 2000 km long source region located close to the equator.
Abstract: We discuss chorus emissions measured by the four Cluster spacecraft at close separations during a geomagnetically disturbed period on 18 April 2002. We analyze the lower band of chorus below one half of the electron cyclotron frequency, measured at a radial distance of 4.4 Earth's radii, within a 2000 km long source region located close to the equator. The characteristic wave vector directions in this region are nearly parallel to the field lines and the multipoint measurement demonstrates the dynamic character of the chorus source region, changing the Poynting flux direction at time scales shorter than a few seconds. The electric field waveforms of the chorus wave packets (forming separate chorus elements on power spectrograms) show a fine structure consisting of subpackets with a maximum amplitude above 30 mV/m. To study this fine structure we have used a sine-wave parametric model with a variable amplitude. The subpackets typically start with an exponential growth phase, and after reaching the saturation amplitude they often show an exponential decay phase. The duration of subpackets is variable from a few milliseconds to a few tens of milliseconds, and they appear in the waveform randomly, with no clear periodicity. The obtained growth rate (ratio of the imaginary part to the real part of the wave frequency) is highly variable from case to case with values obtained between a few thousandths and a few hundredths. The same chorus wave packets simultaneously observed on the different closely separated spacecraft appear to have a different internal subpacket structure. The characteristic scale of the subpackets can thus be lower than tens of kilometers in the plane perpendicular to the field line, or hundreds of kilometers parallel to the field line (corresponding to a characteristic time scale of few milliseconds during the propagation of the entire wave packet). Using delays of time-frequency curves obtained on different spacecraft, we have found the same propagation direction as obtained from the simultaneous Poynting flux calculations. The delays roughly correspond to the whistler-mode group velocity estimated from the cold plasma theory. We have also observed delays corresponding to antiparallel propagation directions for two neighboring chorus wave packets, less than 0.1 s apart.
395 citations