Drivers of the variability of ionospheric plasma observed by the Swarm satellites

The ionosphere is a highly structured plasma that comprises electron density structures that span a wide range of spatial scale sizes. Time of day, season, solar cycle, geomagnetic activity, solar wind conditions, and location all affect large-scale structures, which can span tens to hundreds of kilometres in horizontal extent. While the processes that drive these structures are widely recognised, the relative importance of these processes remains unknown. These large scale structures can also cause smaller-scale anomalies, arising as a result of instability processes. These can affect trans-ionospheric radio transmissions, including those utilised by Global Navigation Satellite Systems (GNSS). The integrity, availability and precision of GNSS systems are all threatened by ionospheric influences. As a result, strategies that are able to anticipate the formation of plasma structures are urgently required.

Swarm is the European Space Agency’s first Earth Observation (EO) satellite constellation mission. Swarm A, Swarm B, and Swarm C were launched into Low Earth Orbit (LEO) in 2013. Their near-polar orbits allow them to sample all longitudes and local time sectors over the course of a year. A variety of data products have been generated to characterise the variability of the ionosphere at horizontal spatial scales of 100 km, 50 km and 20 km. The method of Generalised Linear Modelling is used to determine the primary driving factors of variability at these scale sizes and therefore the conditions at which the integrity and availability of trans-ionospheric radio signals are jeopardised. Statistical relationships between ionospheric features and driving mechanisms are identified at low, middle, auroral and polar latitudes. The differences between time sectors are examined and discussed alongside the physical explanations behind these changes.

This work is within the framework of the Swarm Variability of Ionospheric Plasma (Swarm-VIP) project, funded by ESA in the “Swarm+4D-Ionosphere” framework (ESA Contract No. 4000130562/20/I-DT).