Height‐Integrated Ionospheric Conductances Parameterized By Interplanetary Magnetic Field and Substorm Phase

Abstract

An understanding of ionospheric conductances is important for models of large-scale dynamics in the Earth's magnetosphere. We parameterize height-integrated Pedersen and Hall conductances in the ionosphere, derived from images of auroral emissions obtained by the Defense Meteorological Satellite Programme low-altitude orbiting spacecraft, under different interplanetary and solar wind conditions. For the dayside, conductances are parameterized by interplanetary magnetic field clock angle and magnitude, and by season. These dayside conductances are compared to distributions of field-aligned currents determined from measurements of the Active Magnetosphere and Planetary Electrodynamic Response Experiment. We use these currents to spatially determine a return flow region. We find that the return flow regions exhibit marginally larger conductances than those observed in the polar cap. Conductances in summer exceed those in winter for both the return flow and polar cap regions, on average by a factor of 1.2. On the nightside, we track changes in height-integrated conductance across the Southern Hemisphere polar regions during an average substorm, following a substorm onset list derived from the SuperMAG database. Mean conductances peak approximately 0.75 hr after substorm onset, with maximum conductances seen in the 23 hr magnetic local time sector. Plain Language Summary Low-altitude spacecraft are able to build up images of aurora in the polar regions with low temporal resolution. Using a combination of these images taken in different wavebands, and after applying a model of atmospheric conditions, we can derive parameters such as ionospheric conductance, integrated along the line of sight from the spacecraft. Knowledge of conductances in the high-latitude polar regions is important for our understanding of the large-scale dynamics of the Earth's magnetosphere. We divide our results into two sections. The first section explores conductances in the dayside Northern Hemisphere under the effects of the incoming solar wind and interplanetary magnetic field. We compare these conductances to large-scale patterns of ionospheric currents derived from a separate constellation of satellites. The currents can be used to define certain polar regions, and we compare conductances between these regions. The second section examines conductances under different phases of a substorm, when the magnetosphere is rearranged under the influence of particular driving conditions in the incoming solar wind. The behavior of the conductances is consistent with known patterns of substorm progression, and we show that peak conductances are seen half an hour after substorm onset.

Testing the electrodynamic method to derive height-integrated ionospheric conductances

“…The formulas described by Chapman and Bartels (1940), Haines (1988), and Haines and Torta (1994) were used to derive the "ionospheric equivalent current function" (Kamide et al, 1981;Richmond and Kamide, 1988). A detailed description of the process is provided by Weimer (2019), which includes the separation of the magnetic effects into their internal and external sources.…”

“…The SuperDARN statistical model Greenwald, 1996, 2005) was used to help constrain the fit of E ⊥ . Ground-based magnetometer data were used to construct a map of the divergence-free ionospheric current, J df , using a spherical cap harmonic analysis (SCHA) (Haines, 1988) and the techniques described by Chapman and Bartels (1940) and Backus (1986). The curl-free current, J cf , was derived from magnetic field measurements on the DMSP, Iridium, and Ørsted satellites.…”

Formation of Alfvén Wave Ducts by Magnetotail Flow Bursts

“…The Pedersen conductance in the model ionosphere is taken to be a uniform constant value of 10 S with the Hall conductance setting to zero. Average Pedersen conductance varies with F10.7 (Sheng et al., 2017) and IMF and substorm phase (Carter et al., 2020). A relatively high value of constant Pedersen conductance was chosen for this run because this run is more similar to a substorm, and the Pedersen conductance during geomagnetic activities is typically larger than that during quiet times (e.g., Lam et al., 2019; Lester et al., 1996).…”

Universal Time Variations in the Magnetosphere and the Effect of CME Arrival Time: Analysis of the February 2022 Event that Led to the Loss of Starlink Satellites

“…However, there are a number of points that need to be considered about effects of variations in this solar-EUV-induced conductivity in the polar cap and auroral oval. Much of the energy dissipation during geomagnetic storms takes place in the auroral ovals, caused by the Pedersen currents that connect the Region 1 and Region 2 field-aligned currents and where conductivity is dominated by auroral precipitation rather than being generated by solar EUV (Carter et al, 2020). This greatly reduces the significance of the solar EUV generated conductivity to energy deposition during geomagnetic storms.…”