Plot a) shows the map of the ionospheric irregularities measured around 23:10 UT of January14th over the European sector at latitudes between 45° and 80° N and longitudes between −15° and 25° E. The dark green line represents the trajectory of the Swarm Bravo satellite passing over Europe, from South to North, between 23:07 UT and 23:16 UT on January 14th. The light green line indicates the in-situ plasma density of Swarm Bravo, with a higher longitudinal positive deviation from the ground track, the higher the plasma density is. The other variables follow the same colour description as Figures 7 and 8. Plot b) shows the in-situ electron density measured by Swarm Bravo (red line) between 23:07 UT and 23:16 UT of January 14th over the European sector. The blue dots represent the ROTI values measured by the GNSS. The yellow band represents the enhancement of ROTI between 0.2 and 0.5 TECU/min due to the presence of the poleward boundary of the ionospheric trough.