A New Mechanism for Early-Time Plasmaspheric Refilling: The Role of Charge Exchange Reactions in the Transport of Energy and Mass Throughout the Ring Current-Plasmasphere System

Cold H⁺ produced via charge exchange reactions between ring current ions and exospheric neutral hydrogen constitutes an additional source of cold plasma that further contributes to the plasmasphere and affects the plasma dynamics in the Earth's magnetosphere system; however, its production and associated effects on the plasmasphere dynamics have not been fully assessed and quantified. In this study, we perform numerical simulations mimicking an idealized three-phase geomagnetic storm to investigate the role of heavy ion composition in the ring current (O⁺ vs. N⁺) and exospheric neutral hydrogen density in the production of cold H⁺ via charge exchange reactions. It is found that ring current heavy ions produce more than 50% of the total cold H⁺ via charge exchange reactions, and energetic N⁺ is more efficient in producing cold H⁺ via charge exchange reactions than O⁺. Furthermore, the density structure of the cold H⁺ is highly dependent on the mass of the parent ion; that is, cold H⁺ deriving from charge exchange reactions involving energetic O⁺ with neutral hydrogen, populates the lower L-shells, while cold H⁺ deriving from charge exchange reactions involving energetic N⁺ with neutral hydrogen populates the higher L-shells. In addition, the density of cold H⁺ produced via charge exchange reactions involving N⁺ can be peak at values up to one order of magnitude larger than the local plasmaspheric density, suggesting that solely considering the supply of cold plasma from the ionosphere to the plasmasphere can lead to a significant underestimation of plasmasphere density.

Charge-State-Dependent Energization of Suprathermal Ions During Substorm Injections Observed by MMS in the Magnetotail

Understanding the energization processes and constituent composition of the plasma and energetic particles injected into the near-Earth region from the tail is an important component of understanding magnetospheric dynamics. In this study, we present multiple case studies of the high-energy (≳40 keV) suprathermal ion populations during energetic particle enhancement events observed by the Energetic Ion Spectrometer (EIS) on NASA's Magnetospheric Multiscale (MMS) mission in the magnetotail. We present results from correlation analysis of the flux response between different energy channels of different ion species (hydrogen, helium, and oxygen) for multiple cases. We demonstrate that this technique can be used to infer the dominant charge state of the heavy ions, despite the fact that charge is not directly measured by EIS. Using this technique, we find that the energization and dispersion of suprathermal ions during energetic particle enhancements concurrent with (or near) fast plasma flows are ordered by energy per charge state (E/q) throughout the magnetotail regions examined (~7 to 25 Earth radii). The ions with the highest energies (≳300 keV) are helium and oxygen of solar wind origin, which obtain their greater energization due to their higher charge states. Additionally, the case studies show that during these injections the flux ratio of enhancement is also well ordered by E/q. These results expand on previous results which showed that high-energy total ion measurements in the magnetosphere are dominated by high-charge-state heavy ions and that protons are often not the dominant species above ~300 keV.

Energization of the Ring Current by Substorms

The substorm process releases large amounts of energy into the magnetospheric system, although where the energy is transferred to and how it is partitioned remains an open question. In this study, we address whether the substorm process contributes a significant amount of energy to the ring current. The ring current is a highly variable region, and understanding the energization processes provides valuable insight into how substorm-ring current coupling may contribute to the generation of storm conditions and provide a source of energy for wave driving. In order to quantify the energy input into the ring current during the substorm process, we analyze Radiation Belt Storm Probes Ion Composition Experiment and Helium Oxygen Proton Electron ion flux measurements for H+, O+, and He+. The energy content of the ring current is estimated and binned spatially for L and magnetic local time. The results are combined with an independently derived substorm event list to perform a statistical analysis of variations in the ring current energy content with substorm phase. We show that the ring current energy is significantly higher in the expansion phase compared to the growth phase, with the energy enhancement persisting into the substorm recovery phase. The characteristics of the energy enhancement suggest the injection of energized ions from the tail plasma sheet following substorm onset. The local time variations indicate a loss of energetic H+ ions in the afternoon sector, likely due to wave-particle interactions. Overall, we find that the average energy input into the ring current is ∼9% of the previously reported energy released during substorms.

The plasma environment inside geostationary orbit: A Van Allen Probes HOPE survey

The two full precessions in local time completed by the Van Allen Probes enable global specification of the near-equatorial inner magnetosphere plasma environment. Observations by the Helium-Oxygen-Proton-Electron (HOPE) mass spectrometers provide detailed insight into the global spatial distribution of electrons, H+, He+, and O+. Near-equatorial omnidirectional fluxes and abundance ratios at energies 0.1-30 keV are presented for 2 ≤ L ≤ 6 as a function of L shell, magnetic local time (MLT), and geomagnetic activity. We present a new tool built on the UBK modeling technique for classifying plasma sheet particle access to the inner magnetosphere. This new tool generates access maps for particles of constant energy for more direct comparison with in situ measurements, rather than the traditional constant μ presentation typically associated with UBK. We present for the first time inner magnetosphere abundances of O+ flux relative to H+ flux as a function of Kp, L, MLT, and energy. At L = 6, the O+/H+ ratio increases with increasing Kp, consistent with previous results. However, at L < 5 the O+/H+ ratio generally decreases with increasing Kp. We identify a new "afternoon bulge" plasma population enriched in 10 keV O+ and superenriched in 10 keV He+ that is present during quiet/moderate geomagnetic activity (Kp < 5) at ~1100-2000 MLT and L shell 2-4. Drift path modeling results are consistent with the narrow energy and approximate MLT location of this enhancement, but the underlying physics describing its formation, structure, and depletion during higher geomagnetic activity are currently not understood.

CIR versus CME drivers of the ring current during intense magnetic storms

Ninety intense magnetic storms (minimum Dst value of less than −100 nT) from solar cycle 23 (1996–2005) were simulated using the hot electron and ion drift integrator (HEIDI) model. All 90 storm intervals were run with several electric fields and nightside plasma boundary conditions (five run sets). Storms were classified according to their solar wind driver, including corotating interaction regions (CIRs) and interplanetary coronal mass ejections (ICMEs). Data-model comparisons were made against the observed Dst index (specifically, Dst*) and dayside hot-ion measurements from geosynchronous orbiting spacecraft. It is found that the data-model goodness-of-fit values are different for CIR-driven storms relative to ICME-driven storms. The results are also different for the same storm category for different boundary conditions. None of the CIR-driven events was overpredicted by HEIDI, while the dayside comparisons were comparable for the different drivers. The results imply that the outer magnetosphere is responding differently to the two kinds of solar wind drivers, even though the resulting storm size might be similar. That is, for ICME-driven events, magnetospheric currents inside of geosynchronous orbit dominate the Dst perturbation, while for CIR-driven events, currents outside of this boundary have a systematically larger contribution.

On atmospheric loss of oxygen ions from earth through magnetospheric processes

In Earth's environment, the observed polar outflow rate for O(+) ions, the main source of oxygen above gravitational escape energy, corresponds to the loss of approximately 18% of the present-day atmospheric oxygen over 3 billion years. However, part of this apparent loss can actually be returned to the atmosphere. Examining loss rates of four escape routes with high-altitude spacecraft observations, we show that the total oxygen loss rate inferred from current knowledge is about one order of magnitude smaller than the polar O(+) outflow rate. This disagreement suggests that there may be a substantial return flux from the magnetosphere to the low-latitude ionosphere. Then the net oxygen loss over 3 billion years drops to approximately 2% of the current atmospheric oxygen content.