Characterization of the ionospheric perturbation degree at mid-scales with Swarm's NeGIX and TEGIX

Abstract

Since their launch in November 2013, the European Space Agency's (ESA) Swarm mission has delivered unprecedented data products and services that have significantly enhanced our understanding of solar, magnetospheric, thermospheric, ionospheric, and atmospheric processes, as well as their coupling and impact on human-made technological systems. Currently, the Swarm Product Data Handbook includes 68 Level 1 and Level 2 data products derived from Swarm measurements, along with over 20 additional products obtained from other spacecraft and distributed via the Swarm Data, Innovation, and Science Cluster (DISC).

Recently, two novel data products have been added to the Swarm family: the electron density gradient ionospheric index (NeGIX) and the total electron content gradient ionospheric index (TEGIX). These products implement a temporal and spatial combination of measurements from Swarm A and Swarm C along their near-polar, parallel orbits. NeGIX and TEGIX enable the investigation of ionospheric plasma irregularities and perturbations at mid-scales, on the order of 100 km, not only along the meridional transit direction of the Swarm satellites but also along the longitudinal (zonal) direction. Consequently, the space-based observations from Swarm, combined with the methodologies of NeGIX and TEGIX, provide new insights into several important topics in space weather research. Indeed, initial studies using these products have demonstrated their effectiveness in applications such as scintillation modeling, characterizing ionospheric plasma bubbles, and monitoring ionospheric indices in combination with ground-based observations.

In this work, we provide a comprehensive assessment of the capabilities of NeGIX and TEGIX to characterize the ionospheric state under both quiet and stormy geomagnetic conditions. We examine several of the most intense geomagnetic events from solar cycles 24 and 25. Furthermore, with over ten years of Swarm data available, a climatological analysis of the ionosphere has been conducted using these newly-developed indices. Such analysis forms a foundation for future modeling and combined studies, while also supporting the development of improved proxies for characterizing ionospheric behavior and enabling their practical use in navigation, communication, and remote sensing systems.