Example of electron density recordings by the Swarm satellites of a plasma depletion event at low latitudes. In the top frame, the plasma variations are plotted over magnetic latitude; in the bottom frame, they are showing versus the E-layer footprint of the fluxtube (ApexLat). Low-latitude fluxtubes do not reach satellite heights. In the bottom panel, the magnetic longitude difference (ΔMLon) between the Swarm A/C and Swarm B observations is shown.