A study of ionospheric variability through SWARM and ground-based observations to inform on the variability of radio propagation effects.

Radio waves are subject to a variety of propagation effects when traversing through the ionosphere.  These effects depend on the radio wave frequency as well as on the ionospheric conditions that determine the spatial distribution of plasma density along a given ray path. Ionospheric propagation effects can be determined at various orders of approximation of the Appleton-Hartree equation for the refractive index. These propagation effects vary according to the variability of the ionosphere, which is driven by complex combinations between factors such as solar and magnetic activities, 

This contribution discusses the variability of ionospheric conditions in relation to propagation effects. The ionospheric variability was estimated by using a diverse set of information: ionospheric and magnetic models, in-situ and ground observations.  

Within a timespan of a solar cycle, from November 2013 to November 2024, the European Space Agency's SWARM constellation has enabled unprecedented studies of Earth's Ionosphere and Magnetosphere through the provision of continuous, high temporal and spatial measurements of electron density and magnetic field parameters. In this work electron density and magnetic field in-situ SWARM observations are compared with the IRI model (Bilitza et al., 2017), the IGRF model (Thebault et al., 2015), and with ground observations. Ground-based observations, including electron density parameters recorded by GIRO ionosondes and magnetic field strength recorded by selected magnetometers, collected at geographically diverse locations were compared with SWARM’s in-situ measurements at different magnetic latitudes/longitudes, and under various ionospheric conditions over an entire solar cycle.

This analysis covered an entire solar cycle period and included an assessment of both active and quiet conditions (e.g., through the use of indices such as Kp). 

Initial comparisons between SWARM’s electron density in-situ measurements, GIRO ionosonde observations and the IRI model, as well as between SWARM’s magnetic field strength measurements, ground-based magnetometer data and the IGRF model, seem to suggest a higher ionospheric variability across different latitudes/longitudes, and geomagnetic conditions. The results indicate how a dataset such as offered by SWARM and other similar missions, in synergy with ground-based observations, can form a useful framework to improve the understanding of the ionospheric variability and the corresponding propagation effects.

 

[1] Bilitza, D., Shubin, V., Truhlik, V., Richards, P., Reinisch, B., & Huang, X. (2017). International Reference Ionosphere 2016: From ionospheric climate to real-time weather predictions. Space Weather, 15(2), 418–429.

[2] Thebault, E., Finlay, C. C., Beggan, C. D., Alken, P., Aubert, J., Barrois, O., … & Zhou, B. (2015). International Geomagnetic Reference Field: The 12th generation. Earth, Planets and Space, 67, 79.