This study presents a comprehensive analysis of the 1.5 years’ worth of OGO 6 BIMS data, focusing on the density profiles of ionospheric oxygen and nitrogen ions across various environmental parameters, including solar activity, geomagnetic activity, seasons, latitude, altitude, and magnetic local time. While the abundances of both O+ and N+ decrease monotonically with increasing altitude, the two species follow significantly different power laws, such that nN+ decreases at a slower rate (1/x) than nO+ (1/x2). This leads to a linear increase in the nN+/nO+ ratio with altitude. The average nN+/nO+ ratio reaches its maximum in the midnight sector, whereas the average densities of both oxygen and nitrogen ions peak on the day side. The peak in oxygen ion density leads that of nitrogen ion by 30º in longitude. These differences are most likely due to the different spatio-temporal scales for production and loss for those two ion species. The nN+/nO+ ratio displays a strong seasonal dependence, reaching its highest values during the summer season.

The inductive component of the magnetospheric electric field, which is associated with the temporal change of magnetic field, provides an additional means of local plasma energization and transport in addition to the electrostatic counterpart. This study examines the detailed response of the inner magnetosphere to inductive electric fields and the associated electric-driven convection corresponding to different solar wind conditions. A novel modeling capability is employed to self-consistently simulate the electromagnetic and plasma environment of the entire magnetospheric cavity. The explicit separation of the electric field by source (inductive vs. electrostatic) and subsequent implementation of inductive effects in the ring current model allow us to investigate, for the first time, the effect of the inductive electric field on the kinetics and evolution of the ring current system. The simulation results presented in this study demonstrate that the inductive component of the electric field is capable of providing an additional source for long-lasting plasma drifts, which in turn significantly alter the trajectories of both thermal and energetic particles. Such changes in the plasma drift, which arise due to the inductive electric fields, further reshape the storm-time ring current morphology and alter the degree of the ring current asymmetry, as well as the timing and the peak of the ion pressure. The total ion energy is increasing at a faster rate than the supply of energetic ions to the ring current, suggesting that the inductive electric field provides effective and accumulative local energization for the trapped ring current population without confining additional particles.

Ionospheric outflow supplies nearly all of the heavy ions observed within the magnetosphere, as well as a significant fraction of the proton density. While much is known about upflow and outflow energization processes, the full global pattern of outflow and its evolution is only known statistically or through numerical modeling. Because of the dominant role of heavy ions in several key physical processes, this unknown nature of the full outflow pattern leads to significant uncertainty in understanding geospace dynamics, especially surrounding storm intervals. That is, global models risk not accurately reproducing the main features of intense space storms because the amount of ionospheric outflow is poorly specified and thus magnetospheric composition and mass loading could be ill-defined. This study defines a potential mission to observe ionospheric outflow from several platforms, allowing for a reasonable and sufficient reconstruction of the full outflow pattern on an orbital cadence. An observing system simulation experiment is conducted, revealing that four well-placed satellites are sufficient for reasonably accurate outflow reconstructions. The science scope of this mission could include the following: reveal the global structure of ionospheric outflow; relate outflow patterns to geomagnetic activity level; and determine the spatial and temporal nature of outflow composition. The science objectives could be focused to be achieved with minimal instrumentation (only a low-energy ion spectrometer to obtain outflow reconstructions) or with a larger scientific scope by including contextual instrumentation. Note that the upcoming Geospace Dynamics Constellation mission will observe upwelling but not ionospheric outflow.

Both in situ measurements and numerical simulations show that the charge exchange collisions between energetic ring current ions (>10keV) and cold ambient neutral atoms of the upper atmosphere and exosphere (<1eV) can be a major loss process of the ring current ions. Owing to the high volume of energetic ion source injected from the ion plasma sheet during storm time under strong convection strength, there can be a significant rate of occurrence of charge exchange collision in the inner magnetosphere, therefore contributing a significant amount of inner magnetospheric cold proton populations. Due to the different charge exchange cross sections among different reactions, cold protons are generated at different rates from different energetic ion species. In this study, both qualitative and quantitative assessments on the production and evolution of charge-exchange byproduct cold protons are performed via numerical simulations, showing that the production and evolution of the cold H+ populations can be primarily driven by the plasma sheet conditions combined with the magnetospheric convection, while having the potential to affect the dynamics of the plasmasphere and facilitate the early-stage local plasmaspheric refilling. Furthermore, the energetic heavy ions composition plays an important role determining the cold H+ contribution structure from the energetic ring current ions.

The roles of heavy ions have long been an important subject in the magnetospheric physics since the first discovery of O+ ions in the magnetosphere as it hinted to the connection between the ionospheric and magnetospheric plasma. Albeit limited, several observations show the importance of ionospheric N+ and molecular ions, including NO+, N2+ and O2+, in the high-altitude ionosphere and magnetosphere. However, the mechanisms responsible for accelerating the ionospheric heavy ions from eV to keV energies are still largely unknown. Developed from the Polar Wind Outflow Model (PWOM), the Seven Ion Polar Wind Outflow Model (7iPWOM) solves the gyrotropic transport equations for all relevant species (e-, H+, He+, N+, O+, N2+, NO+ and O2+) along open magnetic field lines and therefore, has the capability to assess the role of heavy ions in the supersonic ionospheric outflow. However, the hydrodynamic approach is limited to the region where collisions are important. For the altitudes above the collision-dominated region, the hydrodynamic solution becomes increasingly inadequate. Thus, the 7iPWOM applies a kinetic particle-in-cell (PIC) approach that enables the inclusion of wave-particle interactions (WPI) and Coulomb collisions. The simulation results showed that the N+ ions play a key role in the polar wind solution under all conditions. The mechanisms responsible for the energization of outflowing N+ ions are different than those of O+, not only in the collision-dominated region but also at high-altitudes. This means that the local heating sources to O+ and N+ in the polar wind, even in small amounts, can lead to plasma instability and could possibly affect the large-scale transport properties. In addition, the relative abundance of molecular ions, and how they change the polar wind solution, reveals the link between lower thermosphere and the ionosphere. Therefore, tracking the molecular ions helps understand how the “fast ion outflow” acquires sufficient energy in such a short time scale, compared with the dissociative recombination lifetime of the molecular ions, and assess the role of molecular ions in the overall dynamics of the polar wind outflow.

Nitrogen is the most abundant element in the Earth’s atmosphere. Around 78% N2; and 21% O2; form the air we breathe and expand into high-altitude atmosphere, the thermosphere, and eventually the ionosphere. The neutral molecules in the ionosphere are ionized by solar radiation, and some of them break up into atoms, and others become charged particles. The ionospheric ions with sufficient energy can flow out into space, and the abundances of these outflowing ionospheric ions highly impact the near-Earth plasma properties. Studies focused on outflowing O+ ions have been conducted for many years. However, the contribution of N+ to the outflow solution is still largely unknown due to the instrumental limitations. We developed a first-principled physics model to understand how N+ and molecular ions, including NO+, N2+, and O2+, acquire the sufficient energy to escape Earth’s atmosphere. This study reveals the importance of N+ ions in the high-altitude polar ionosphere, from few hundred kilometers to thousands of kilometers in the space, and examines the possible mechanisms to accelerate and removed them from Earth’s atmosphere.

Changes in the heavy ion composition in the terrestrial ionosphere and magnetosphere can have significant impact on particle dynamics in the Earth’s magnetosphere-ionosphere system. Most instruments flying in space, such as MMS and Van Allen Probes, lack the possibility to distinguish N+ from O+ due to their close masses. However, observations of N+ both in the ionosphere and magnetosphere indicate that N+ is a constant companion of O+ , especially during the storm time. Because N+ originates from the Earth’s ionosphere, we further develop the Polar Wind Outflow Model (PWOM) to investigate the behavior and acceleration mechanisms of heavy ions in Earth’s ionosphere. The PWOM solves the particle dynamics of O+, H+ and He+ in the ionospheric outflow and the modified PWOM can further simulate the behavior of N+ and N2+ in Earth’s polar wind. The escape of heavy ions from the Earth atmosphere is consequences of energization and transport mechanisms, including photo ionization, electron precipitation, ion-electron-neutral chemistry and collisions. The modified PWOM is coupled with a two-stream model of superthermal electrons (GLobal airglow, or GLOW) to deal with attenuated radiation, electron beam energy dissipation, and secondary electron impact. In this study, we show that during various solar conditions, the ion-electron-neutral densities in the ionospheric outflow show significant difference when we consider N+ ions in the polar wind. Furthermore, we will compare the simulation results of the modified PWOM with observation data for validation.

The question of how many satellites it would take to accurately map the spatial distribution of ionospheric outflow is addressed in this study. Given an outflow spatial map, this image is then reconstructed from a limited number virtual satellite pass extractions from the original values. An assessment is conducted of the goodness of fit as a function of number of satellites in the reconstruction, placement of the satellite trajectories relative to the polar cap and auroral oval, season and universal time (i.e., dipole tilt relative to the Sun), geomagnetic activity level, and interpolation technique. It is found that the accuracy of the reconstructions increases sharply from one to a few satellites, but then improves only marginally with additional spacecraft beyond ~4. Increased dwell time of the satellite trajectories in the auroral zone improves the reconstruction, therefore a high-but-not-exactly-polar orbit is most effective for this task. Local time coverage is also an important factor, shifting the auroral zone to different locations relative to the virtual satellite orbit paths. The expansion and contraction of the polar cap and auroral zone with geomagnetic activity influences the coverage of the key outflow regions, with different optimal orbit configurations for each level of activity. Finally, it is found that reconstructing each magnetic latitude band individually produces a better fit to the original image than 2-D image reconstruction method (e.g., triangulation). A high-latitude, high-altitude constellation mission concept is presented that achieves acceptably accurate outflow reconstructions.

Charged particles are observed to be injected into the inner magnetosphere region from plasma sheet, and energized up to high energies over short distance and time, during both geomagnetic storms and substorms. Numerous studies suggest that it is the short-duration and high-speed plasma flows, which are closely associated with the global effects of magnetic reconnection and inductive effects, rather than the slow and steady convection that control the Earth-ward plasma transport and magnetic flux from the magnetotail, especially during geomagnetic activities. In order to include the effect of inductive electric produced by the temporal change of magnetic field on the dynamics of ring current, we implemented both theoretical and numerical modifications to an inner magnetosphere kinetic model—Hot Electron-Ion Drift Integrator (HEIDI). New drift terms associated with the inductive electric field are incorporated into the calculation of bounce-averaged coefficients for the distribution function, and their numerical implementations and the associated effects on total drift and energization rate are discussed. Numerical simulations show that the local particle drifts are significantly altered by the presence of inductive electric fields, in addition to the changing magnetic gradient-curvature drift due to the distortion of magnetic field, and at certain locations, the inductive drift dominates both the potential and the magnetic gradient-curvature drift. The presence of a self consistent inductive electric field alters the overall particle trajectories, energization, and pitch angle, resulting in significant changes in the topology and strength of the ring current.

The escape of heavy ions from the Earth atmosphere is consequences of energization and transport mechanisms, including photoionization, electron precipitation, ion-electron-neutral chemistry and collisions. Numerous studies considered the outflow of O ions only, but ignored the observational record of outflowing N. In spite of 12% mass difference, N and O ions have different ionization potentials, ionospheric chemistry, and scale heights. We expanded the Polar Wind Outflow Model (PWOM) to include N as well as key molecular ions in the polar wind. We refer to this model expansion as the Seven Ion Polar Wind Outflow Model (7iPWOM), which involves expanded schemes for suprathermal electron impact and ion-electron-neutral chemistry and collisions. Numerical experiments, designed to probe the influence of season, as well as that of solar conditions, suggest that N is a significant ion species in the polar ionosphere and its presence largely improves the polar wind solution, as compared to observations.