Michael H. Denton

On Geostationary Operational Environmental Satellites (GOES) 8–15 (1996–2020), the Energetic Particle Sensor (EPS) included three integral electron channels, with nominal lower energies of 0.6 MeV (E1), 2 MeV (E2) and 4 MeV (E3). The 2 MeV channel has received more attention than the other two channels, because it is used by the NOAA Space Weather Prediction Center for its radiation belt real‐time alerts, and because the characterizations of E1 and E3 were ambiguous, due in part to processing changes between GOES‐12 and ‐13. This paper reports the first cross‐calibration of EPS E1 and E3 with the new Magnetospheric Particle Sensor—High Energy (MPS‐HI) (first flown on GOES‐16). It is based on observations from 2019, when GOES‐15 and ‐17 were separated by 0.6 hr local time on average. The channel response functions ( sr vs. energy) were used three ways: in a bowtie analysis using the method used for the GOES‐17 calibrations; in forward‐model analyses to predict rates for comparison with observations; and in a spectral inversion for comparison of differential energy spectra from the two instruments. The results show that the GOES 13–15 characterizations were more accurate than the GOES 8–12 characterizations, and the bowtie characterization of E3 is still more accurate, while the GOES 13–15 characterization of E1 should continue to be used. The EPS E1 bias with respect to MPS‐HI is 69%. In the E3 energy range, the EPS fluxes are lower than MPS‐HI, from a factor of 2 at 3 MeV to a factor of 5 at 4.4 MeV.

Spacecraft surface charging in the inner magnetosphere often occurs in the pre‐midnight to the dawn sector when electron fluxes of tens of keV increase. Inner magnetosphere ring current models can be used to simulate/predict the spacecraft surface charging environment, with their outer boundary conditions specified either based on observations or provided by other models, such as MHD models. In the latter approach, using MHD quantities, the flux spectrum at the outer boundary is commonly assumed to follow a Kappa or Maxwellian distribution function. Such a method however often departs greatly from the realistic spectrum at E < tens of keV, a crucial energy range in the surface charging anomaly. In order to achieve a better representation of the surface charging environment, we propose to combine the MHD‐parameterized flux spectrum with an empirical electron flux model of E < 40 keV to set the electron flux boundary condition. Results indicate that as opposed to the case where the MHD‐parameterized flux distribution is solely used at the model boundary, simulations with the new boundary condition yields a more intense surface charging environment. The integrated electron flux between 10 < E < 50 keV, a measure of the severity of the surface charging environment, is significantly enhanced by 1‐2 orders of magnitude, leading to a much better agreement with Van Allen Probes measurements. This study hence demonstrates a reasonable solution to the setting of outer boundary conditions for inner magnetosphere models and is recommended for coupled geospace circulation models.

Satellite surface charging often occurs in the inner magnetosphere from the pre-midnight to the dawn sector when electron fluxes of  hundreds of eV to tens of keV are largely enhanced. Inner magnetosphere ring current models can be used to simulate/predict the satellite surface charging environment, with their flux outer boundary conditions specified either based on observations or provided by other models, such as MHD models. In the latter approach, the flux spectrum at the outer boundary is usually assumed to follow a Kappa or Maxwellian distribution, which however often departs greatly from, or underestimates, the realistic distribution below tens of keV, the energy range that is crucial in the spacecraft surface charging anomaly. This study aims to optimize the electron flux boundary condition of the inner magnetosphere ring current model to achieve a better representation of the surface charging environment. The MHD-parameterized flux spectrum is combined with an empirical electron flux model that specifies the < 40 keV electron flux spectrum. New simulation results indicate that the surface charging environment, monitored by an integrated electron flux between 10<E<50 keV, is significantly enhanced by 1-2 orders of magnitude as opposed to the case in which Kappa/Maxwellian distribution is used at the outer boundary. The new results therefore show better agreement with Van Allen Probes measurements. The improved boundary condition also impacts the auroral precipitation, which may change the conductivity and circulated dynamics. 

Challenges faced in the quantitative use of long-term radiation belt data sets include establishing their relative accuracy and correcting for on-orbit degradation. An existing empirical model of energetic plasmas (0.001–40 keV) in geosynchronous orbit has been extended in energy to several hundred keV by incorporating observations from the Geostationary Operational Environmental Satellite (GOES) 13 and 15 magnetospheric electron detector (MAGED) and magnetospheric proton detector (MAGPD). In order to ensure the accuracy of this energy range extension, the following steps were taken: (1) removing noise bursts; (2) intra-calibrating the nine solid state telescopes comprising each MAGED or MAGPD; (3) cross-calibrating GOES 13 and 15; and (4) cross-calibrating magnetospheric plasma analyzer (MPA) and GOES fluxes, the necessary final step in augmenting an MPA-based model with GOES data. The MAGED and MPA electron fluxes were demonstrated to agree well at the energy (40 keV) where they overlap, while the MAGPD proton fluxes exhibited a severe long-term degradation compared to MPA. This problem is related to the well-known long-term degradation of the proton fluxes from the similar medium energy proton and electron detector (MEPED) proton telescopes on the POES and Metop satellites in low-Earth orbit. Results of this on-orbit calibration work are used to reconsider long-standing hypotheses about the cause of degradation in similar proton telescopes.

The Earth’s plasmasphere contains cold (~eV energy) dense (>100 cm-3) plasma of ionospheric origin. The primary ion constituents of the plasmasphere are H+ and He+, and a lower concentration of O+. The outer part of the plasmasphere, especially on the duskside of the Earth, drains away into the dayside outer magnetosphere when geomagnetic activity increases. Because of its high density and low temperature, this plasma has the potential to modify magnetic reconnection at the magnetopause. To investigate the effect of plasmaspheric material at the magnetopause, Magnetospheric Multiscale (MMS) data are surveyed to identify magnetopause crossings with the highest He+densities. Plasma wave, ion, and ion composition data are used to determine densities and mass densities of this plasmaspheric material and the magnetosheath plasma adjacent to the magnetopause. These measurements are combined with magnetic field measurements to determine how the highest density plasmaspheric material in the MMS era may affect reconnection at the magnetopause.

Electromagnetic ion cyclotron (EMIC) waves can act as a loss process for both ring current ions and radiation belt electrons, and the spatial and temporal characteristics of these waves are important for quantifying their effects on energetic particles. Here we utilize observations from multiple spacecraft to constrain the azimuthal and radial dimensions as well as the duration of an EMIC wave event occurring on the nightside of the inner magnetosphere on 7 July 2013. These combined observations reveal waves limited to a narrow radial extent but persisting ~10+ hr and spanning ~12 hr in local time. The solar wind conditions, geomagnetic activity, and plasma environment are also examined to better understand the conditions under which persistent nightside EMIC waves can occur. Relativistic electron phase space density profiles during this event reveal local minima concurrent with the wave activity, consistent with EMIC‐driven scattering and loss of radiation belt electrons.

When the interplanetary magnetic field is northward for a period of time, O⁺ from the high‐latitude ionosphere escapes along reconnected magnetic field lines into the dayside magnetopause boundary layer. Dual‐lobe reconnection closes these field lines, which traps O⁺ and mass loads the boundary layer. This O⁺ is an additional source of magnetospheric plasma that interacts with magnetosheath plasma through magnetic reconnection. This mass loading and interaction is illustrated through analysis of a magnetopause crossing by the Magnetospheric Multiscale spacecraft. While in the O⁺‐rich boundary layer, the interplanetary magnetic field turns southward. As the Magnetospheric Multiscale spacecraft cross the high‐shear magnetopause, reconnection signatures are observed. While the reconnection rate is likely reduced by the mass loading, reconnection is not suppressed at the magnetopause. The high‐latitude dayside ionosphere is therefore a source of magnetospheric ions that contributes often to transient reduction in the reconnection rate at the dayside magnetopause.

An existing empirical model of the electron fluxes at geosynchronous orbit is extended radially outward in the equatorial plane to ~6–20 Earth radii (R_E) using observations from the Research with Adaptive Particle Imaging Detectors (RAPID) instrument on the Cluster spacecraft. The new model provides electron flux predictions in the energy range ~45 eV to ~325 keV, as a function of local time and radial distance from the Earth, with geomagnetic activity parameterized by the Kp index. The model outputs include the mean and median electron fluxes along with the standard deviation and the 5th, 25th, 75th, and 95th percentiles for the given input conditions. The flux outputs from the model are tested against in‐sample observations from Cluster/RAPID and out‐of‐sample observations from Time History of Events and Macroscale Interactions during Substorms (THEMIS)/Solid State Telescope with good prediction efficiency during quiet and active intervals, as quantified by standard methods. This new model is intended to supplement current predictive capabilities in the magnetosphere for spacecraft operations, as well as providing the necessary boundary and/or input conditions for computational/physical models of the magnetospheric system when the necessary in situ observations are unavailable. While the new model can certainly not reproduce the rapid small‐scale fluctuations inherent in spacecraft observations, it does provide a coarse capability to predict the flux of electrons close to the equatorial plane, based on radial distance, energy, local time, and geomagnetic activity, in regions where no in situ assets are available.

A four‐plasma classification scheme is used to categorize the ACE solar wind data set into four types of plasma: (1) coronal‐hole‐origin plasma, (2) streamer‐belt‐origin plasma, (3) sector‐reversal‐region plasma, and (4) ejecta. The statistical properties of the solar wind fluctuations at 1 AU are analyzed for each of the four types of plasma in the years 1998–2008 using ACE magnetic field and plasma measurements. Between the four types of solar wind plasma there are subtle statistical differences in the spectral indices of (a) trace‐B, (b) trace‐v, (c) total energy, (d) magnetic intensity, and (e) plasma number density. Between the four types of plasma there are significant statistical differences (a) in the Elsässer inward and outward spectral indices, (b) in the outward imbalance, (c) in the Alfvénicity, (d) in the normalized vector‐B, vector‐v, magnetic intensity, and number density fluctuation amplitudes, (e) in the population of strong current sheets, (f) in the population of sudden velocity shears, (g) in the anisotropies of magnetic field and velocity fluctuations, and (h) in the parallel‐to‐B magnetic field fluctuation spectral index. It is argued that the four‐plasma categorization scheme is superior to a slow‐versus‐fast categorization for the study of turbulence and fluctuations in the solar wind.