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.

Common solar wind drivers behind magnetic storm-magnetospheric substorm dependency

The dynamical relationship between magnetic storms and magnetospheric substorms is one of the most controversial issues of contemporary space research. Here, we address this issue through a causal inference approach to two corresponding indices in conjunction with several relevant solar wind variables. We find that the vertical component of the interplanetary magnetic field is the strongest and common driver of both storms and substorms. Further, our results suggest, at least based on the analyzed indices, that there is no statistical evidence for a direct or indirect dependency between substorms and storms and their statistical association can be explained by the common solar drivers. Given the powerful statistical tests we performed (by simultaneously taking into account time series of indices and solar wind variables), a physical mechanism through which substorms directly or indirectly drive storms or vice versa is, therefore, unlikely.