How Magnetically Conjugate Atmospheres and the Magnetosphere Participate in the Formation of Low‐Energy Electron Precipitation in the Region of Diffuse Aurora

Abstract

The electron precipitation in the region of the diffuse aurora should be considered as a two‐step process (Khazanov et al., 2017, https://doi.org/10.1002/2016GL072063). The first one is the interaction of plasma sheet electrons with electrostatic electron cyclotron and/or whistler waves, moving those electrons into the loss cone to precipitate in both magnetically conjugate atmospheres. The second step is the interaction of these electrons with the ionosphere and atmosphere via their elastic and nonelastic collisions and reflection (backscatter) of degraded electrons back to magnetosphere and conjugate ionospheres. This paper presents the results of a newly developed scenario of nonsteady‐state electron precipitation dynamics that accounts for magnetosphere‐ionosphere‐atmosphere energy interplay over the entire energy range of the plasma sheet electron population and their affiliated secondary electrons. It also studies how both magnetically conjugate auroral regions work together with the magnetosphere in the formation of electron precipitation in the region of the diffuse aurora with the energy range coverage from 1 eV up to 10 keV.

ASHLEY: A New Empirical Model for the High‐Latitude Electron Precipitation and Electric Field

“…The strong low‐energy tail shown in the ASHLEY‐A energy spectrum (Figure 8a) is frequently seen in observations (e.g., Evans, 1974; Fung & Hoffman, 1988; Hardy et al., 1985; McIntosh & Anderson, 2014; Wing et al., 2019) and its sources are considerably complex since the electron precipitation is not a simple one‐way transport of electrons from the magnetosphere to the ionosphere (Khazanov & Glocer, 2020 and references therein). For example, if a field‐aligned potential drop is present, the upgoing electrons without sufficient kinetic energy to overcome such potential drop will be reflected downward and subsequently are observed as downward precipitation flux (Evans, 1994; Evans & Moore, 1979; Richards, 2013).…”

“…For example, if a field-aligned potential drop is present, the upgoing electrons without sufficient kinetic energy to overcome such potential drop will be reflected downward and subsequently are observed as downward precipitation flux (Evans, 1994;Evans & Moore, 1979;Richards, 2013). In addition, it is also possible that the upgoing superthermal electrons from the conjugate hemisphere contribute to the formation of the low-energy tail (Khazanov & Glocer, 2020). Meier et al (1989) developed an empirical formula (hereafter, M89 formula) to account for the low-energy tail which was later used in the model developed by Strickland et al (1993).…”

“…Nevertheless, it was found that a Maxwellian spectrum may significantly underestimate the soft electron precipitation when comparing with the energy spectrum from measurements, sometimes by orders of magnitude (e.g., McIntosh & Anderson, 2014;Wing et al, 2019). However, additional types of energy spectra different from a Maxwellian spectrum have been included in recently developed electron precipitation models (e.g., Newell et al, 2009Newell et al, , 2014Zhang et al 2015), soft electron precipitations may still be underestimated owing to deficient precipitation spectral identification techniques (Wing et al, 2019) and incomplete inclusion of soft electron precipitations from different sources (Khazanov & Glocer, 2020). Therefore, to better specify the altitudinal distribution of Joule heating in GCMs and improve the GCM accuracy, it is critical to develop a new electron precipitation model that can better specify the soft electron precipitations.…”

The Precipitated Electrons in the Region of Diffuse Aurora Driven by Ionosphere‐Thermosphere Collisional Processes

“…(1999, 2009), LBC and UBC wave emissions can last for several hours, continuously pushing plasmasheet electrons into the loss cone with the follow up MI energy interplay as shown in Figure 1a. From the other side, as demonstrated by Khazanov and Glocer (2020), it takes only several minutes for the precipitating primary electron flux of magnetospheric origin to reach a steady‐state condition at ionospheric altitudes. Therefore, such a continuous pumping of electron precipitation into both the magnetically conjugate ionospheres and the follow up of particle interchange between conjugate ionospheres and the magnetosphere create a unique situation where electron energy fluxes can build up and exceed that which is instantaneously provided by the magnetosphere alone.…”

“…This terminology has been accepted for a long time and still remains very useful in auroral studies. The electrons of the ionospheric origin, it should be noted, not only include the secondary electron population that is born in the local hemisphere, but are also contributed to by the IT collisional processes in the magnetically conjugate hemisphere and loss cone trap zones energy interchange (Khazanov et al., 2017) that form the lower energy (10 s of eV) precipitating electron population at ionospheric altitudes (Khazanov & Glocer, 2020) as well as the thermal electron conductivity fluxes that maintain the electron temperature gradient in the topside ionosphere (Khazanov et al., 2020).…”