Search for: All records

Abstract 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. 

Abstract Observations from past space missions report on the significant abundance of N⁺, in addition to those of O⁺, outflowing from the terrestrial ionosphere and populating the near‐Earth region. However, instruments on board current space missions lack the mass resolution to distinguish between the two, and often the role of N⁺in regulating the magnetosphere dynamics, is lumped together with that of O⁺ions. For instance, our understanding regarding the role of electromagnetic ion cyclotron (EMIC) waves in controlling the loss and acceleration of radiation belt electrons and ring current ions has been based on the contribution of He⁺and O⁺ions only. We report the first observations by Van Allen Probes of linearly polarized N⁺EMIC waves, which confirm the presence of N⁺in the terrestrial magnetosphere, and open up new avenues to particle energization, loss, and transport mechanisms, based on the altered magnetospheric plasma composition. 

Abstract Charged particles are observed to be injected into the inner magnetosphere from the 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 earthward transport of plasma and magnetic flux from the magnetotail, especially during geomagnetic activities. In order to include the effect of the inductive electric field 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. 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 the strength of the ring current. 

Abstract The escape of heavy ions from the Earth atmosphere is a consequence 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⁺and 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 production 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. 

This paper reviews a few important concepts and findings pertaining to the ring current research. Also briefly overviewed are the sources and losses of ring current ions. Recent challenges in modeling and observations of the ring current are presented, as is a brief discussion on open questions.