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.
Using tens to hundreds of keV proton and electron flux measurements and simultaneous magnetic field measurements from three Geostationary Operational Environmental Satellites GOES‐13 (75°W), GOES‐14 ...(105°W), and GOES‐15 (135°W), we investigate proton and electron injections and their relationship to the substorm current wedge at geosynchronous altitude. Proton and electron injection processes occur only in the initial formation of the substorm current wedge, the width of which is less than 2 hr in local time in the premidnight region, for moderate substorms. Proton injections are closely related to the formation of a substorm current wedge at geosynchronous altitude, and thus the onset of a substorm, even before local dipolarization in the magnetic field. Proton injections take place only under the western upward field‐aligned currents of the current wedge. Electron injections in the energy range of <100 keV are tightly coupled with local dipolarization in the magnetic field, and these take place mostly in the central region of the current wedge, extending in the region under the western upward field‐aligned currents.
Key Points
Particle injections proceed during the initial formation of a substorm current wedge at geosynchronous altitude
Particle injections occur in the limited extent in the premidnight region, the width of which is less than 2 hr in local time
Proton injections occur even prior to local dipolarization, while electron injections are tightly coupled with local dipolarization in the magnetic field
Observations from the recent Whole Heliosphere Interval (WHI) solar minimum campaign are compared to last cycle's Whole Sun Month (WSM) to demonstrate that sunspot numbers, while providing a good ...measure of solar activity, do not provide sufficient information to gauge solar and heliospheric magnetic complexity and its effect at the Earth. The present solar minimum is exceptionally quiet, with sunspot numbers at their lowest in 75 years and solar wind magnetic field strength lower than ever observed. Despite, or perhaps because of, a global weakness in the heliospheric magnetic field, large near‐equatorial coronal holes lingered even as the sunspots disappeared. Consequently, for the months surrounding the WHI campaign, strong, long, and recurring high‐speed streams in the solar wind intercepted the Earth in contrast to the weaker and more sporadic streams that occurred around the time of last cycle's WSM campaign. In response, geospace and upper atmospheric parameters continued to ring with the periodicities of the solar wind in a manner that was absent last cycle minimum, and the flux of relativistic electrons in the Earth's outer radiation belt was elevated to levels more than three times higher in WHI than in WSM. Such behavior could not have been predicted using sunspot numbers alone, indicating the importance of considering variation within and between solar minima in analyzing and predicting space weather responses at the Earth during solar quiet intervals, as well as in interpreting the Sun's past behavior as preserved in geological and historical records.
The effects of solar radiation storms at Earth are felt across a number of technology‐based industries. Energetic particles present during these storms impact electrical components on spacecraft, ...disrupt high frequency radio communications, and pose a radiation risk for passengers and crew on polar flight routes, as well as for astronauts. An essential aspect of space weather forecasting is therefore to predict the occurrence and properties of a solar proton event before it occurs. In this study, we review radiation storm products issued by the National Oceanic and Atmospheric Administration's Space Weather Prediction Center (SWPC) during Solar Cycles 23 and 24. These include three‐day probabilistic proton event forecasts and short‐term Warning and Alert hazard products. We present performance metrics and forecast skill scores for SWPC probabilistic forecasts and Warning products, which can be used as a benchmark for assessing the performance of radiation storm forecast models.
Plain Language Summary
Energetic events occurring at the Sun, such as solar flares and coronal mass ejections, can accelerate protons, electrons and ions to high energies. These energetic particles can travel towards Earth where they are observed as a solar radiation storm. These storms can impact a number of technology‐based systems and industries. For example, the energetic particles present during these storms impact electrical components on spacecraft, disrupt high frequency radio communications, and pose a radiation risk for passengers and crew on polar flight routes, as well as for astronauts. An essential aspect of space weather forecasting is therefore to predict the occurrence and properties of a solar proton event before it occurs. The National Oceanic and Atmospheric Administration Space Weather Prediction Center (SWPC) issues space weather forecasts for solar radiation storms. In this study, we compare these forecasts with observations to determine how accurate the forecasts were. In particular the paper reviews forecasts between January 1996 and December 2019, a time period covering the last two Solar Cycles. The results of this paper can be used to test new forecasting models to determine if they would be capable of improving SWPC forecasts.
Key Points
For Solar Cycle 24, Space Weather Prediction Center day 1 probabilistic proton forecasts have a Brier Skill Score of 0.25 over persistence
The ≥10 MeV proton Warnings have a Probability of Detection (POD) of 91% and a False Alarm Ratio (FAR) of 24% with a median lead time of 88 min
The ≥100 MeV proton Warnings have a POD of 53% and a of FAR 38% with a median lead time of 10 min
We investigate how relativistic electrons are lost from the Earth's magnetosphere in order to better understand the dynamic variability of the radiation belts. We identify 52 events where the >2 MeV ...electron flux at geostationary orbit decreases rapidly and use a superposed epoch analysis of multispacecraft data to characterize the accompanying solar wind and geomagnetic conditions and examine the relevance of potential loss mechanisms. The results show that the flux decrease events follow a common sequence. The electron flux is reduced first in the dusk sector concurrent with the stretching of the magnetic field to a more tail‐like configuration. The extreme stretching at dusk is caused by the formation of a partial ring current driven by changing solar wind conditions. We investigate three possible causes of the ensuing flux decrease: adiabatic electron motion in response to the changing magnetic field topology, drift out the magnetopause boundary, and precipitation into the atmosphere. The analysis reveals that the flux depletion is likely due to enhanced precipitation into the atmosphere, but the exact cause of the enhanced precipitation is still uncertain.
The National Oceanic and Atmospheric Administration's Space Weather Prediction Center (NOAA/SWPC) issues several solar radiation storm products: the long standing proton Warnings and Alerts that are ...based on particle intensity levels observed by the Geostationary Operational Environmental Satellites; and the more recent International Civil Aviation Organization (ICAO) radiation advisories which specify effective dose rates at aviation flight levels. SWPC ICAO advisories are supported by the U.S. Federal Aviation Administration (FAA) CARI‐7A model. In this paper we use CARI‐7A modeling results for the Ground Level Enhancement 69 (GLE69) solar radiation storm which occurred on the 20th of January 2005 to demonstrate the ICAO advisory format. For the onset and peak of GLE69, we find that a severe (SEV) radiation advisory would have been issued for altitudes above 32,000 ft, for polar and mid latitude regions of the northern and southern hemisphere. At lower altitudes, down to 25,000 ft, the moderate (MOD) radiation threshold would have been exceeded. In total, 10 ICAO radiation advisories would have been issued over 6.5 hr. From the retrospective modeling of GLE69, and feedback from users, we identify ways in which the ICAO advisories should be improved.
Plain Language Summary
The National Oceanic and Atmospheric Administration's Space Weather Prediction Center (NOAA/SWPC) issues products related to solar radiation storms, defined as periods when the number of energetic particles in space are elevated because of enhanced solar activity. Traditionally these products have been based on observations by NOAA's Geostationary Operational Environmental Satellite, indicating the intensity of the storm outside the Earth's atmosphere. New advisories for the International Civil Aviation Organization (ICAO) alert operators when the radiation environment at aviation flight levels is enhanced. At SWPC, ICAO radiation advisories are supported by the U.S. Federal Aviation Administration CARI‐7A model. We present CARI‐7A modeling results for a solar radiation storm which occurred on the 20th of January 2005. At the peak of the storm, we find that radiation advisories would have been issued down to 25,000 ft, for polar and mid latitude regions of the northern and southern hemisphere. The issued advisories would have been updated periodically to keep forecast users informed as to which flight levels were impacted. In total, SWPC would have been issuing ICAO radiation advisories for 6.5 hr. The results identify several ways in which the ICAO advisory format could be improved to prevent people receiving unnecessary warnings.
Key Points
Radiation advisories for the International Civil Aviation Organization (ICAO) provide regional information for users
During GLE69 the ICAO SEVERE radiation threshold was exceeded in the polar and mid latitude bands down to 32,000 ft
Based on the current format, large geographic regions are likely to receive unnecessary ICAO radiation advisories
Since 1998, the GOES system has made eastward and westward observations of multi‐MeV solar proton fluxes. The gyrocenters of the fluxes observed looking westward (eastward) lie outside (inside) ...geostationary orbit. Due to this “east‐west effect,” eastward observations of 4.2–82 MeV protons vary with respect to their westward equivalents. At times of high solar wind dynamic pressure (Pdyn > 10 nPa), the “inside” and “outside” fluxes are approximately equal. As Pdyn decreases to ∼1 nPa and the ring current decreases, the “inside” fluxes decrease as much as an order of magnitude with respect to the “outside” fluxes. Under low Pdyn, the “inside” fluxes exhibit short‐lived (1–3 hr) increases, sometimes to the levels of the “outside” fluxes, during periods of enhanced AE index activity. This association suggests that magnetotail topologies associated with substorms enhance the access of solar protons to lower L shells under low Pdyn.
We develop and test a methodology to determine the relativistic electron phase space density distribution in the vicinity of geostationary orbit by making use of the pitch‐angle resolved energetic ...electron data from three Los Alamos National Laboratory geosynchronous Synchronous Orbit Particle Analyzer instruments and magnetic field measurements from two GOES satellites. Owing to the Earth's dipole tilt and drift shell splitting for different pitch angles, each satellite samples a different range of Roederer L* throughout its orbit. We use existing empirical magnetic field models and the measured pitch‐angle resolved electron spectra to determine the phase space density as a function of the three adiabatic invariants at each spacecraft. Comparing all satellite measurements provides a determination of the global phase space density gradient over the range L* ∼ 6–7. We investigate the sensitivity of this method to the choice of the magnetic field model and the fidelity of the instrument intercalibration in order to both understand and mitigate possible error sources. Results for magnetically quiet periods show that the radial slopes of the density distribution at low energy are positive, while at high energy the slopes are negative, which confirms the results from some earlier studies of this type. We further show that the observed gradients near geosynchronous are generally small, making them very sensitive to both calibration and magnetic field model choice. This paper lays the foundation for this method for future applications to disturbed periods and for future inclusion of additional satellite data.
The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) on the Lunar Reconnaissance Orbiter (LRO) characterizes the radiation environment to be experienced by humans during future lunar ...missions. CRaTER measures the effects of ionizing energy loss in matter due to penetrating solar energetic protons (SEP) and galactic cosmic rays (GCR), specifically in silicon solid-state detectors and after interactions with tissue-equivalent plastic (TEP), a synthetic analog of human tissue. The CRaTER investigation quantifies the linear energy transfer (LET) spectrum in these materials through direct measurements with the lunar space radiation environment, particularly the interactions of ions with energies above 10 MeV, which penetrate and are detected by CRaTER. Combined with models of radiation transport through materials, CRaTER LET measurements constrain models of the biological effects of ionizing radiation in the lunar environment as well as provide valuable information on radiation effects on electronic systems in deep space. In addition to these human exploration goals, CRaTER measurements also provide new insights on the spatial and temporal variability of the SEP and GCR populations and their interactions with the lunar surface. We present here an overview of the CRaTER science goals and investigation, including: an instrument description; observation strategies; instrument testing, characterization, and calibration; and data analysis, interpretation, and modeling plans.
The Space Environment In‐Situ Suite on the Geostationary Operational Environmental Satellite (GOES)‐R series of satellites includes a new instrument for measuring radiation belt electrons and ...protons, the Magnetospheric Particle Sensor–High Energy (MPS‐HI). The MPS‐HI electron channels cover the energy range 50 keV to 4 MeV. The conversion of raw MPS‐HI electron telescope counts to fluxes is based on the so‐called bowtie technique. The goal of the bowtie analysis is to calculate for each energy channel an energy/geometric factor pair applicable to a wide range of energy spectra and for which the geometric factor error is minimized. Rather than using idealized analytical spectral functions, we use observed high‐resolution spectra from the cross‐calibrated Combined Release and Radiation Effects Satellite (CRRES) Medium Electron Sensor A and High Energy Electron Fluxmeter data set from the period 1990–1991, restricted to 6 < L < 8. One thousand randomly selected CRRES spectra are used to perform the bowtie analysis and determine the MPS‐HI channel energy/geometric factor characteristics. The results are used to convert the GOES‐16/‐17 MPS‐HI electron counts to fluxes. The same bowtie technique is used to calculate effective energies and geometric factors for the GOES‐13/‐14 Magnetospheric Electron Detector ME1‐ME5 (30–600 keV) electron channels. We compare the fluxes from the various spacecraft (GOES‐16/‐13, GOES‐17/‐14, and GOES‐16/‐17) over periods of several months to determine the applicability and utility of the bowtie analysis. Finally, we compare the GOES‐16/‐13 fluxes during 22 days of near conjunction. All comparisons show good agreement among the various satellite data sets.
Key Points
Development of a bowtie technique for the calibration of the GOES‐R satellite series SEISS MPS‐HI electron data
Cross‐satellite comparison of the electron data sets from various GOES satellites
Comparison of the >2‐MeV electron channel (used for space weather alerts by SWPC) with the analogous channel from older instruments
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