Swarm and Digisonde observations on September 17, 2015 (a) the topside scale-height at Swarm altitude calculated with the α-C-SD model, the Swarm electron density Ne and the Swarm irregularity indices gradient ED at 20 km, 50 km and 100 km during the 90 s of the satellite pass over the Digisonde from 19:11:19 UTC to 19:12:37 UTC. (b) The Digisonde electron density profile and the reconstructed topside electron density with the α-C-SD model in a red color trace; the green color trace represents the insitu Swarm ED observed during the Swarm pass over the Digisonde.