Ionosphere-thermosphere coupling during the 22–23 June 2015 geomagnetic storm: Swarm and FPI coordinated observations above the Oukaimeden observatory

We investigate the response of the ionosphere-thermosphere coupled system to the 22-23 June 2015 geomagnetic storm in the region above the Oukaimeden observatory in Morocco with a Fabry-Perot interferometer and the Swarm satellites. The measured thermospheric neutral winds are strong enough to have two direct consequences. First, they create a strong asymmetry in the equatorial ionisation crests on both sides of the magnetic equator (actually, they make the southern hemisphere crest disappear). This asymmetry is explained by the southerly thermospheric neutral wind that was blowing during the storm and is shown to be favoured by the season. Second, within the northern hemisphere ionisation crest, Swarm A and C detect km-size electron density structures. Those may be ascribed to gradient drift instability.