Relation of the Plasmapause to the Midlatitude Ionospheric Trough, the Sub‐Auroral Temperature Enhancement and the Distribution of Small‐Scale Field Aligned Currents as Observed in the Magnetosphere by THEMIS, RBSP, and Arase, and in the Topside Ionosphere by Swarm

Abstract

The relation between the plasmapause (PP) and various ionospheric phenomena, such as the midlatitude ionospheric trough (MIT) has been studied for decades. More recently, it was found that the equatorward boundary of small‐scale field‐aligned currents (SSB) and the PP are also closely coupled. In spite of prolonged efforts many details of these relationships, as well as the mechanisms responsible for them remain poorly understood. ESA's Swarm mission in conjunction with magnetospheric missions (RBSP, Arase, and THEMIS) provides an unprecedented opportunity to study these relationships on a global scale and over an extended period. Swarm delivers observations of MIT, the associated sub‐auroral electron temperature enhancement (SETE), as well as SSB, while PP crossings can be inferred from in‐situ magnetospheric electron density measurements. In this study, we use 7 years of Swarm observations and PP positions from 2014 to 2017 to address some of the open questions. We confirm that MIT/SETE and PP are directly coupled, however only in the nighttime. Their correlation remains high after post‐dawn, however, with an increasing, MLT‐dependent time lag. Afternoon MIT observations were found conjugated with a plasmaspheric plume. The correlation between SSB and PP is also high and they intersect each other near MLT midnight. Our results confirm the scenario that the PP is formed on the night side, and propagates to the dayside by co‐rotating with the Earth and suggest that the plasma is transported from the depleted ionospheric/dense plasmaspheric stagnation region also westward/sunward forming the afternoon MIT/narrow plumes, respectively.

The evolving paradigm of the subauroral geospace

“…The MPF's polarization shorting approach, where the plasmapause separates the SAID from the "fresh," innermost border of PS electrons, provides a consistent explanation of the long-known statistical facts. First, since the main ionospheric trough is adjacent to the ionospheric footprint of the plasmapause (Yizengaw and Moldwin, 2005;Heilig et al, 2022), "fresh" SAID channels are mapped on the trough's poleward boundary. Then, the plasmasphere's shrinkage due to the increasing convection and erosion (Goldstein et al, 2003) makes the plasmapause move closer to Earth.…”

Sub‐Auroral Ion Drifts (SAID) Developed Over the Northern Winter Hemisphere at Dawn During 2016–2017

“…The resent study of Heilig et al. (2022) confirms the direct coupling of plasmapause and MIT/SETE and the formation of new plasmapause on the nightside in the 21‐06 magnetic local time (MLT) sector.…”

Stormtime Ring Current Heating of the Ionosphere and Plasmasphere

“…The CIMI simulation shows that direct heating of the ionosphere occurs only during the peak of the storm, after heat conduction has already elevated the ionosphere electron temperature relative to the No Heating case. Further observations and modeling are needed to explore these processes and to place them into the context of other observed phenomena at or near the plasmapause, such as sub‐auroral electron temperature enhancements (Heilig et al., 2022) and stable auroral red arcs (Cornwall et al., 1971; Mendillo et al., 2016).…”