Electron distribution function formation in regions of diffuse aurora

Abstract

The precipitation of high‐energy magnetospheric electrons (E ∼ 600 eV–10 KeV) in the diffuse aurora contributes significant energy flux into the Earth's ionosphere. To fully understand the formation of this flux at the upper ionospheric boundary, ∼700–800 km, it is important to consider the coupled ionosphere‐magnetosphere system. In the diffuse aurora, precipitating electrons initially injected from the plasma sheet via wave‐particle interaction processes degrade in the atmosphere toward lower energies and produce secondary electrons via impact ionization of the neutral atmosphere. These precipitating electrons can be additionally reflected upward from the two conjugate ionospheres, leading to a series of multiple reflections through the magnetosphere. These reflections greatly influence the initially precipitating flux at the upper ionospheric boundary (700–800 km) and the resultant population of secondary electrons and electrons cascading toward lower energies. In this paper, we present the solution of the Boltzman‐Landau kinetic equation that uniformly describes the entire electron distribution function in the diffuse aurora, including the affiliated production of secondary electrons (E < 600 eV) and its energy interplay in the magnetosphere and two conjugated ionospheres. This solution takes into account, for the first time, the formation of the electron distribution function in the diffuse auroral region, beginning with the primary injection of plasma sheet electrons via both electrostatic electron cyclotron harmonic waves and whistler mode chorus waves to the loss cone, and including their subsequent multiple atmospheric reflections in the two magnetically conjugated ionospheres. It is demonstrated that magnetosphere‐ionosphere coupling is key in forming the electron distribution function in the diffuse auroral region.

The Magnetosphere‐Ionosphere Electron Precipitation Dynamics and Their Geospace Consequences During the 17 March 2013 Storm

“…As was shown by Khazanov et al (2015Khazanov et al ( -2018, these processes greatly influence the total precipitating flux at the upper ionospheric boundary (around about 800 km). The precipitating and SEs can also reflect back into the magnetosphere and then undergo multiple reflections at the magnetic conjugate points.…”

“…The STET code models all sources and collisional processes of electrons as they travel along a magnetic field line through the magnetosphere and ionosphere (Khazanov et al, 2015;Khazanov, Himwich, et al, 2016;Khazanov et al, 2017b) with participation of both magnetically conjugate regions. It simulates nonsteady formation of electron distribution functions kinetically along 1-D in space and 2-D in velocity space (energy and pitch angle).…”

“…Khazanov (2011) and Khazanov et al (2014Khazanov et al ( , 2015Khazanov et al ( , 2017b; ; Khazanov, Himwich, et al, (2016) provide extensive details on the current version of the STET code. Khazanov (2011) and Khazanov et al (2014Khazanov et al ( , 2015Khazanov et al ( , 2017b; ; Khazanov, Himwich, et al, (2016) provide extensive details on the current version of the STET code.…”

“…As has been shown by Khazanov et al (2014) about 15-40% of the total aurora energy returns back to the magnetosphere and the conjugate ionosphere. As discussed by Khazanov et al (2015), , 2017a, the first step in such simulations is initiation of electron precipitation from the Earth's plasma sheet via wave-particle interactions (WPIs) into both magnetically conjugate points (e.g., as is simulated by Chen, Lemon, Guild, et al, 2015). As discussed by Khazanov et al (2015), , 2017a, the first step in such simulations is initiation of electron precipitation from the Earth's plasma sheet via wave-particle interactions (WPIs) into both magnetically conjugate points (e.g., as is simulated by Chen, Lemon, Guild, et al, 2015).…”

“…Collisionless processes dominate in the inner magnetosphere, whereas collisional interactions are important in the ionosphere, and Khazanov et al (2018) have emphasized that first-principle simulations of precipitating electron fluxes in both regimes are required to understand spatial and temporal variations of ionospheric conductance and related electric fields. The second step is to account for multiple atmospheric reflections of electrons between the ionosphere and magnetosphere at the two magnetically conjugate points, as treated in the SuperThermal Electron Transport (STET) model (Khazanov et al, 2015(Khazanov et al, , 2017a(Khazanov et al, , 2017b(Khazanov et al, , 2018Khazanov, Himwich, et al, 2016). The second step is to account for multiple atmospheric reflections of electrons between the ionosphere and magnetosphere at the two magnetically conjugate points, as treated in the SuperThermal Electron Transport (STET) model (Khazanov et al, 2015(Khazanov et al, , 2017a(Khazanov et al, , 2017b(Khazanov et al, , 2018Khazanov, Himwich, et al, 2016).…”