Ionospheric Electron Density and Conductance Changes in the Auroral Zone During Substorms

Abstract

Substorm is the complicated global magnetospheric reconfiguration process of a few hours in duration, which includes intensification of large-scale magnetospheric convection, field-aligned currents, and auroral precipitation (Baker et al., 1996). All its manifestations are temporally variable and spatially structured. Although it is customary to distinguish three substorm phases (growth, expansion and recovery phases), the expansion phase shows the most violent changes and energy transformations in both the magnetosphere and ionosphere. Particularly during that time period, explosively enhanced earthward plasma flows bring accelerated particles and magnetic flux into the nightside inner magnetosphere, producing the magnetic field dipolarization and injecting energetic plasma (e.g., Gabrielse et al., 2019). Drifting around the Earth, this energetic plasma precipitates into the ionosphere. Energetic electron precipitations (EEP, with energies above a few tens keV) produce ionization in the D-and E-regions; auroral electron and proton precipitations modify E and F region. These changes are of large practical importance: The enhanced and structured ionization in the high-latitude ionosphere deeply affects many aspects of important human activities, including navigation, radio communications, etc., which needs modeling, prediction, and monitoring of these changes (see recent detailed discussion of these aspects in Fiori et al., 2020). Existing ionospheric models, such as NeQuick and IRI (Radicella, 2009;Bilitza et al., 2017; etc.), cannot reproduce the ionospheric response on substorm timescale. Assessing the substorm effects on high-latitude ionization is an important step in developing ionospheric models and operational tools.One approach to model and predict the ionization changes is to characterize the variable auroral particle precipitation spectra. Being observed on many low altitude polar spacecraft for a few decades, these observations provide a basis for statistical empirical models of precipitation (e.g., Hardy et al., 1987;

Substorm‐Time Ground dB/dt Variations Controlled by Interplanetary Shock Impact Angles: A Statistical Study

“…The Fukushima theorem (Fukushima, 1994) states that, in all regions below the ionosphere, magnetic fields generated from field-aligned currents and their corresponding Pedersen currents cancel each other out. However, this theorem is only valid for the ionosphere with constant conductance, which is not the case during storms and substorms when conductances can vary by a few siemens (Stepanov et al, 2021). More details of the use of the SECS technique to obtain dB/dt variations can be found elsewhere (Weygand, 2021;Weygand et al, 2011Weygand et al, , 2012.…”

“Obstanovka” experiment on determining spacecraft surface charging aboard the International Space Station

“…In many papers, e.g., [McPherron and Chu, 2018;Stepanov et al, 2021], the mid-latitude positive magnetic bays, associated with "classical" sustorms, are interpreted as the effects of the appearance of the dipolarization process and the substorm West Travelling Surge (WTS) formation. The analysis of the satellites and ground data performed in [Safargaleev et al, 2020] fit to the near-tail current disruption scenario as a possible source of the dipolarization and WTS, associated with polar substorm onset.…”

The Key Role of Magnetic Curvature Scattering in Energetic Electron Precipitation During Substorms

“…A crucial element of substorm injections is the energetic electron precipitation (EEP) into the ionosphere (e.g., Gabrielse et al., 2019; Gkioulidou et al., 2012; Sergeev et al., 2020). Depending on their energy, precipitating electrons can penetrate down to the E/D‐layer (below 80 km, see Nikolaev et al., 2021; Oyama et al., 2017; Stepanov et al., 2021), where they can impact ionospheric chemistry (Mironova et al., 2019; Seppälä et al., 2015; Verronen et al., 2021), lead to mesospheric ozone loss (Chapman‐Smith et al., 2023), increase local conductance (Yu et al., 2018), and contribute to large‐scale ionosphere disturbances (Lyons et al., 2021; Nishimura et al., 2021).…”