Rare opportunity to compare topside in-situ electron densities from Swarm satellites with ionosonde

The ESA Swarm mission comprises a constellation of three identical satellites (Swarm A, B and C) at low-altitude polar orbits operating since 2014. The initial orbit heights were at around 465km (Swarm A and C) and 520 (Swarm B) at an inclination of 87.35° for Swarm A/C and 87.75° for Swarm B. The mission has provided a long-term in-situ electron density dataset from Langmuir Probes from each of these three satellites. Since the constellation operates in the topside ionosphere it is impossible to compare these electron density values with the established Bottomside electron density profile monitoring techniques such as ionosondes which are considered as the most widely used ground-based instruments for ionospheric monitoring. However occasionally, during severe geomagnetic storms, due to the dramatic uplift of the F-region, the altitude scope of ionosondes can be extended to cover the orbit altitude of such satellite missions as Swarm. Such an example was the geomagnetic storm on May 10-13, 2024 known as the Mother’s Day geomagnetic superstorm. In this study, we attempt a comparison based on a limited dataset of electron density values from ionosondes at Swarm orbit altitude to examine the level of agreement between these two techniques.