Comparative analysis of ground- and space-based ionospheric indices for monitoring the perturbation degree of the ionosphere

Abstract

Ionospheric indices play a crucial role in monitoring and understanding the dynamic behavior of the ionosphere. By examining the temporal and spatial variability of Total Electron Content (TEC) or electron density, we can detect and characterize ionospheric perturbations across various scales. Beyond their scientific value, these indices also help assess the potential impact of space weather on the availability, accuracy, and functionality of modern radio systems used for telecommunications, navigation, and remote sensing.

Several ionospheric proxies have proven effective in estimating the degree of ionospheric perturbations at medium and large scales. However, indices such as the Rate of TEC Index (ROTI), the Disturbance Ionosphere indeX Spatial Gradient (DIXSG), the Gradient Ionosphere indeX (GIX), and the Sudden Ionospheric Disturbance indeX (SIDX) primarily rely on ground-based GNSS measurements, which are limited to observation sites mostly located in populated regions. In contrast, space-based measurements offer global coverage. In this context, ESA’s Swarm satellites have been providing high-quality data and services for more than a decade, enriching our understanding of space weather phenomena and their impact on human activities. The Swarm Ionospheric Bubble Index (IBI) detects sub-kilometer plasma bubbles in magnetic field measurements, while the Ionospheric Plasma IRregularities Index (IPIR) uses Langmuir Probe measurements along satellite tracks to estimate electron density gradients at scales of up to 100 km. Additionally, the newly developed TEC Gradient Index (TEGIX) and Electron Density Gradient Index (NeGIX) complement Swarm’s data products, enabling the estimation of spatial horizontal gradients at scales of approximately 100 km. The relevance of Swarm data products is further enhanced by recent efforts to provide them with a near-real-time Fast Track latency.

In this work, we present a comparative analysis using some of the ground- and space-based indices mentioned above and examine their potential to characterize the perturbation degree of the ionosphere. By comparing their performance, we aim to determine how strongly the indices correlate with one another and whether one can substitute another. For example, Swarm products may be used to estimate ionospheric perturbations for GNSS operators and users over oceans or in regions with limited ground-based data availability. The analysis is applied to events of strongly perturbed geomagnetic conditions, such as the Mother’s Day storm of 2024 and the St. Patrick’s Day storm of 2015, as well as to quiet conditions with little indication of ionospheric gradients. Although our results show a strong correlation between the ground- and space-based indices for the selected periods and regions, their overall performance and applicability require further analysis, which will be discussed in more detail during this presentation.

Such complimentary studies are essential for advancing space weather science and improving monitoring and forecasting capabilities. They also help in developing effective mitigation strategies and enhancing the resilience of technological systems against the effects of space weather.