Topside Equatorial Ionospheric Plasma Density, Temperature, Composition, and Drifts Measurements at Jicamarca Under June Solstice, Moderate Solar Flux Conditions

Abstract

State parameter profiles in the equatorial topside ionosphere were measured in June, 2023, and late July and early August, 2025, at the Jicamarca Radio Observatory. The measurements combined multiple radar pulsing schemes and analysis methods. In 2025, for the first time, plasma drifts were measured concurrently with electron densities, electron and ion temperatures, and ion composition by exploiting a new electronic beam steering capability. Significant quiet-time day-to-day variability is evident across all measurements. In this study, variability in the vertical drifts is considered as a source of variability in the other plasma state parameters. Topside temperatures and the midday temperature depression in particular are examined for sensitivity to vertical drifts. While predictions obtained from the SAMI2-PE model, which includes energetic electron transport, exhibit reasonable agreement with observations overall, they do not account for topside variability. Some limitations of the measurements and the model along with strategies for improvement and further study are discussed.