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 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.