Ionospheric Connections (ICON) Ion Velocity Meter (IVM) Observations of the Equatorial Ionosphere at Solar Minimum

Abstract

The Ionospheric CONnections (ICON) mission has been continuously operating during the period from January 2020 to December 2021 providing simultaneous measurements of the thermal plasma properties near 600 km altitude and the neutral atmosphere and ionosphere in the altitude range 100 km to 500 km at low and middle latitudes. During this period of extremely low to moderately low solar activity, the evolving properties of the topside ionospheric density, composition, temperature and drift velocity at the satellite location are described using measurements from the Ion Velocity Meter (IVM). In the early months of 2020, the very low solar activity and relatively high abundance of H⁺ in the total plasma density present a challenge to a robust description of the full local time distribution of the topside ion drifts. However, the quality of measurements of the ionospheric composition and temperature are not impacted by low solar activity conditions and changes in the O⁺ and H⁺ concentrations and their effects on the energy balance in the topside can be investigated as solar activity changes. As the relative abundance of O⁺ increases, the susceptibility of the ion drift determination to the local plasma environment around the spacecraft is reduced and a more robust determination of the ion drift at all local times is possible. From October 2020 onward, the relationships between the topside ionospheric dynamics and the ionospheric density and temperature can be investigated and the relationships between the plasma drifts and the underlying neutral wind drivers can be established.