Technical Article

New Swarm products NeGIX and TEGIX for monitoring horizontal ionospheric gradients

¹ Institute for Solar-Terrestrial Physics, German Aerospace Center (DLR), Kalkhorstweg 53, 17235 Neustrelitz, Germany
² Swedish Institute of Space Physics (IRF), Box 537, 751 21, Uppsala, Sweden
³ Division of Geomagnetism and Geospace, Technical University of Denmark (DTU), Centrifugevej 356, 2800 Kgs. Lyngby, Denmark

^* Corresponding author: andres.cahuasqui@dlr.de

Received: 4 April 2025
Accepted: 18 September 2025

Abstract

The detection, monitoring, and characterization of ionospheric perturbations are key areas of space weather research due to their significant impact on man-made technological systems. The European Space Agency’s (ESA) Swarm mission has provided high-quality data and services for more than 11 years, enriching our understanding of solar, magnetospheric, thermospheric, ionospheric, and atmospheric processes, as well as their coupling and effects on human activities. As part of the Swarm Data, Innovation, and Science Cluster (DISC) project “Monitoring Ionospheric GRAdients at Swarm (MIGRAS)”, we have developed two novel Swarm data products to study the state and dynamics of the ionosphere at Swarm height and medium scales – in the order of 100 km. We introduce and validate the electron density spatial gradient index, NeGIX, and the total electron content (TEC) gradient index, TEGIX. We leverage the near-polar, parallel orbits of Swarm A and C to combine data with a resolution of 0.5° in latitude along the satellite tracks. NeGIX uses electron density measurements from the Langmuir Probe experiment onboard Swarm A and C, while TEGIX uses Precise Orbit Determination (POD) data from the Swarm TEC product. We validate these indices for both quiet and perturbed geomagnetic conditions, and further comparison is made with the Swarm Ionospheric Plasma IRregularities (IPIR) product and the ground-based Gradient Ionosphere indeX (GIX). The zonal component of the NeGIX and TEGIX gradients, and particularly their meridional component, clearly identify ionospheric perturbations in the selected case studies. These indices have a high potential for detecting ionospheric perturbations during storm events and provide valuable information about their dynamical evolution. It is expected that NeGIX and TEGIX may essentially support ionospheric research, practical applications, and low-latency monitoring services.