Abstract When particles from the radiation belts impinge on the atmosphere, they can be absorbed into the atmosphere or deflected back into the magnetosphere. The deflection of particles back into the magnetosphere is known as backscatter, and it is a key link connecting the atmosphere to the magnetosphere—involving collisions with atmospheric neutrals, magnetic mirroring, the production of secondary emissions, and energy transfer from the particle to the atmosphere. Backscatter is both a feedback mechanism to magnetospheric precipitation drivers and an indirect measure of atmospheric energy absorption, making it an important process to quantify and understand. In this work, we use data from the Electron Fields and Losses INvestigation (ELFIN) satellites to quantify backscatter rates. We find that backscatter rates vary between during periods of loss cone filling and during periods without loss cone filling. We then compare the ELFIN backscatter data to the results of an updated and improved Monte Carlo‐based simulation and find excellent agreement with ELFIN‐measured backscatter rates. Finally, we use our improved Monte Carlo model to characterize the pitch angle and energy dependence of backscatter and the pitch angle distributions of backscattered electrons, finding results consistent with previous modeling efforts.
Abstract Dispersionless injection, involving sudden, simultaneous flux enhancements of energetic particles over a broad range of energy, is a characteristic signature of the particles that are experiencing a significant acceleration and/or rapid inward transport process. To provide clues to the physical processes that lead to the acceleration and transport of energetic ions in the dispersionless injection region, we conduct superposed epoch analyses of 75 dispersionless injection events identified by Van Allen Probes with focus on the species‐ and azimuthal angle‐ ( φ ) dependent signatures of ∼50–600 keV ions inside geosynchronous orbit. Our analysis shows that, on average, the light (hydrogen and helium) ion fluxes undergo a rapid, transient enhancement, while the heavy (oxygen) ion fluxes exhibit a more gradual, persisting enhancement. Such a species‐dependent behavior could be explained in terms of different gyro‐radius of the ion species. For events where the proton injection onset is 30–60 s earlier than the electron one, proton fluxes initially increase at small φ values (i.e., tailward guiding centers) and then at larger φ values (earthward ones). The initial signatures suggest a result of the earthward transport of injected protons, as seen at the explosive growth phase. For events where both electron and proton fluxes increase simultaneously, on the other hand, proton fluxes isotropically increase with no significant φ dependence. Such an isotropic proton flux enhancement may imply a local process in which charged protons are rapidly accelerated to higher energies at the spacecraft location.
AbstractThe paper contains a detailed analysis of the formation of an auroral spiral based on hitherto not published observations by the all‐sky camera in Kilpisjärvi, Northern Finland. We conclude that spirals appearing during a substorm form by a modification of the interface between tail and magnetosphere, the location of the generator current of the westward electrojet. Driven by the arriving flow bursts, this current is subject to ruptures by the appearance of a sequence of hook‐like structures. These structures can move eastward with speeds up to 3 km/s. The propagation is attributed to a constructive magnetic fracture process driven from behind by the power of the arriving flow bursts. Poleward bending and extension of a hook‐like structure, followed by a turning to the west and then equatorward, is the first step in spiral formation. It becomes the primary spiral arm, if a poleward arm grows out of weaker auroral structures, poleward and eastward of it. We suggest that the upward field‐aligned currents related to the bright spiral arms are largely balanced by adjacent downward currents. The electric fields associated with the connecting Pedersen currents are consistent with the counter‐clockwise motion. An important additional ingredient in the observed configuration is an eastward directed flow field, which is the generator of an additional upward current and possibly crucial for the spiral formation. Electric field data from literature throw confusing light on the propagation of a spiral, whether like a vessel in the ocean or by incorporating the magnetic flux ahead of it.
Abstract In situ measurements of the solar wind have been available for almost 60 years, and in that time plasma physics simulation capabilities have commenced and ground‐based solar observations have expanded into space‐based solar observations. These observations and simulations have yielded an increasingly improved knowledge of fundamental physics and have delivered a remarkable understanding of the solar wind and its complexity. Yet there are longstanding major unsolved questions. Synthesizing inputs from the solar wind research community, nine outstanding questions of solar wind physics are developed and discussed in this commentary. These involve questions about the formation of the solar wind, about the inherent properties of the solar wind (and what the properties say about its formation), and about the evolution of the solar wind. The questions focus on (1) origin locations on the Sun, (2) plasma release, (3) acceleration, (4) heavy‐ion abundances and charge states, (5) magnetic structure, (6) Alfven waves, (7) turbulence, (8) distribution‐function evolution, and (9) energetic‐particle transport. On these nine questions we offer suggestions for future progress, forward looking on what is likely to be accomplished in near future with data from Parker Solar Probe, from Solar Orbiter, from the Daniel K. Inouye Solar Telescope (DKIST), and from Polarimeter to Unify the Corona and Heliosphere (PUNCH). Calls are made for improved measurements, for higher‐resolution simulations, and for advances in plasma physics theory.
George V. Khazanov, Viviane Pierrard, Qianli Ma
et al.
AbstractPlasmasphere plays an important role in the magnetospheric physics, defining many important inputs to the ionosphere from the middle to the auroral latitudes. Among them are electron thermal heat fluxes resulting from the Coulomb interaction of superthermal electrons (SE) and cold plasmaspheric electrons. These fluxes define the electron temperature at the upper ionospheric altitudes and are the input to the global ionospheric modeling networks. As was previously found from the calculation of lower energy SE and thermal heat fluxes, the knowledge of field‐aligned cold plasma distribution in the plasmasphere is a very sensitive parameter that introduces the most uncertainties in the calculation of these values. To verify the previously used SuperThermal Electron Transport code assumptions regarding plasmaspheric field‐aligned density structure ∼[B(s)/Bo]a, we used the latest version of 3D plasmaspheric model developed by Pierrard, Botek, and Darrouzet (2021, https://doi.org/10.3389/fspas.2021.681401). Such an assumption is found to be very reasonable in the calculations of electron thermal heat fluxes entering upper ionospheric altitudes and the associated electron temperature formation for the two selected dayside and nightside electron precipitation events driven by whistler‐mode wave activity.
AbstractJupiter's magnetic field is tilted by ∼10° with respect to the planet's spin axis, and as a result the Jovian plasma sheet passes over the Galilean satellites at the jovigraphic equator twice per planetary rotation period. The plasma and magnetic field conditions near Ganymede's magnetosphere therefore change dramatically every ∼5 hr, creating a unique magnetosphere‐magnetosphere interaction, and on longer time scales as evidenced by orbit‐to‐orbit variations. In this paper, we summarize the typical magnetic field conditions and their variability near Ganymede's orbit as observed by the Galileo and Juno spacecraft. We fit Juno data from orbit 34, which included the spacecraft's close Ganymede flyby in June 2021, to a current sheet model and show that the magnetospheric conditions during orbit 34 were very close to the historical average. Our results allow us to infer the upstream conditions at the time of the Juno Ganymede flyby.
AbstractA novel multispacecraft solar wind monitor is developed, which expands on the forecasting ability of OMNI by giving spatially resolved predictions. The prediction algorithm ingests all the data from the current fleet of three L1 monitors, allowing gradients in the solar wind to be resolved on scale sizes similar to the magnetosphere. Understanding structure of the solar wind is vital to determine the global magnetospheric configuration, which is important in both real time as a space‐weather product and data users wanting to know upstream conditions when interpreting observations. The model is validated by comparing the predictions with other spacecraft observing the solar wind in situ. We perform a statistical study with thousands of hours of magnetospheric multiscale observations in the solar wind, comparing the prediction accuracy of the multispacecraft monitor to all of the OMNIWeb single‐spacecraft monitors. The multispacecraft monitor shows improvement over all three of the single‐spacecraft predictions for 44% of the cases and also outperforms both ACE and Wind, which are the primary magnetic field contributors to the OMNI IMF prediction, 55% of the time. We propose that the realistic structure of the solar wind that is resolved with multiple solar wind monitors could be vitally important to implement as upstream conditions in global magnetospheric simulations.
AbstractThis paper discusses my recollections concerning the origins of space radio and plasma wave research at the University of Iowa. My career in space research started when I was hired as a freshman engineering student by Prof. James A. Van Allen in April 1958, shortly after his discovery of Earth's radiation belts with Explorer 1, the first U.S. satellite. My early work mainly involved digital data system designs for the University of Iowa “Injun” series of satellites, the first satellites completely designed and constructed at a university. It was on Injun 3 that, at the suggestion of Prof. Brian J. O'Brien, I developed one of the very first radio and plasma wave instruments ever flown on a spacecraft. This instrument made the first pioneering studies of a wide variety of space radio and plasma wave phenomena, such as whistlers, chorus, and auroral hiss. These early studies were soon followed by somewhat similar NASA‐funded Iowa radio and plasma wave instruments that were used to explore Earth's magnetosphere with the Injun‐5, S3‐A, Hawkeye, IMP, and ISEE satellites, the solar wind with the Helios 1 and 2 spacecraft, and the outer planets and interstellar space with the Voyager 1 and 2 spacecraft. My discussions of this very early era in space research, and the key people involved, are limited to the time period before roughly 1980.
AbstractSignificant steady but slow variability of radiation belt proton intensity, in the energy range ∼19–200 MeV and for L<2.4, has been observed in an empirical model derived from data taken by Van Allen Probes during 2013–2019. It is compared to predictions of a theoretical model based on measured initial and boundary conditions. Two aspects of the variability are considered in detail and require adjustments to model parameters. Observed inward transport of proton intensity maxima near L=1.9 and associated increasing intensity are caused in the model by inward radial diffusion from an external source while conserving the first two adiabatic invariants. The diffusion coefficient is constrained by these observations and is required to have increased near the start of 2015 by a factor ∼2. Observed decay of proton intensity at L<1.6 can be caused only in part by energy loss to free and bound electrons in the local plasma and neutral atmosphere. Another, unknown loss mechanism is required to match observed proton decay rates as a function of energy. Accounting for the expected influence of slow radial diffusion at low L, the additional loss should have a mean lifetime near 22 years, independent of L and energy in the range ∼19–70 MeV. Several candidate loss mechanisms are considered—added plasma or neutral density, elastic Coulomb scattering, plasma wave scattering, field‐line curvature scattering, and collision with orbital debris—but none are found viable.
AbstractFor the past decade, the Lyman‐alpha detectors on board National Aeronautics and Space Administration's Two Wide‐angle Imaging Neutral‐atom Spectrometers (TWINS) mission have obtained routine measurements of solar Lyman‐α photons (121.6 nm) resonantly scattered by atomic hydrogen (H) in the terrestrial exosphere. These data have been used to derive global three‐dimensional (3‐D) models of exospheric H density beyond 3 RE, which are needed to understand various aspects of aeronomy and heliophysics, such as atmospheric chemistry and energetics, magnetospheric energy dissipation, ion‐neutral coupling, and atmospheric evolution through gravitational escape. These empirical distributions are obtained through parametric fitting of assumed functional forms that have little observational justification, thus limiting confidence in conclusions drawn from analysis of the resulting exospheric structure. In this work, we present a new means of global 3‐D reconstruction of exospheric H density through tomographic inversion of the scattered H Lyman‐α emission. Our approach avoids the conventional dependence on ad hoc parametric formulations and, based on the case studies reported here, appears to enable a more accurate characterization of the global structure of the H density in the outer exosphere. We evaluate the bounds of technique feasibility using simulated TWINS data and report new geophysical insights gained from applying this promising new approach to an example of actual TWINS data.
Abstract The pH dependence of the steady state parameters of the glucose oxidase (EC 1.1.3.4, from Aspergillus niger) reaction was determined by O2-monitored experiments over the entire pH range from 3 to 10 at 25°, with d-glucose as substrate. The data were fitted to a three-parameter steady state rate equation and the significance of the steady state parameters was examined by stopped flow half-reaction and turnover measurements at the extremes of the pH range used. The major conclusions from these studies can be summarized as follows. 1. At low pH, in the presence of halide, the maximum turn-over number (kcat) is determined entirely by the rate of flavin reduction (k2) in the reductive half-reaction. Furthermore, substrate combines only with an unprotonated form of the oxidized enzyme and the reductive half-reaction can be represented as follows. H+ E0 (K1)/⇄/(H+) E0 + S (k1)/⇄/(k-1) E0 - S (k2)/→ Er + δ-lactone Since kcat and k2 are both specifically decreased by halides at low pH values, it is probable that the turnover rate in the low pH range is also limited by k2 in the absence of halide. The steady state absorption spectrum of E0 - S is indistinguishable from the spectrum of E0. This finding, together with the fact that removal of the 1-hydrogen from d-glucose is a ratelimiting process in flavin reduction is consistent with both a hydride transfer mechanism and with a flavin-glucose adduct mechanism in which this adduct is relatively unstable and never accumulates significantly as a kinetic intermediate. 2. The importance of k2 as a limiting first order process in turnover diminishes as the pH is raised. Thus, at pH 10 the major first order process in turnover is the breakdown of a species of oxidized enzyme, E'0, in the oxidative half-reaction. The rate of this process at pH 10.0 is 214 sec-1, whereas k2 has a value of 800 sec-1. 3. The reduced enzyme exists in two kinetically significant states of ionization, Er and Er-. The rapid reoxidation of Er with O2, to regenerate E0, is predominant at pH values less than 7. At pH values greater than 7, a much less rapid reaction of Er- with O2, leading to the formation of E'0-, becomes increasingly important. The species E'0- is unreactive with glucose and it is the conversion of a protonated form of E'0- to E0 which principally governs kcat at pH values greater than 7. We present a complete kinetic scheme describing the effects of pH and discuss the possible chemical significance of the species E'0.
The erd2 protein is the receptor responsible for recycling proteins bearing the carboxyl-terminal sequence KDEL (single-letter amino acid code) to the endoplasmic reticulum, following their loss from that organelle by the process of forward transport. To study the interaction of erd2p with the sequence KDEL we have reconstituted binding of erd2p to its ligand in vitro. Binding in vitro exhibits the same sequence specificity as retention of lumenal proteins in vivo and is strikingly sensitive to pH. Our results raise the possibility that erd2p-mediated sorting of lumenal endoplasmic reticulum proteins is facilitated by the pH differences between compartments of the secretory pathway.