May 2024 severe geomagnetic storm suppressed mid-latitude ionospheric E-region formation mechanism

The Ionospheric E-region is primarily formed during the day through the photoionization of molecular oxygen and molecular nitrogen. During the severe geomagnetic storm on May 2024, this paper reports that, over the mid-latitudes, this formation mechanism was significantly disrupted causing large-scale suppression of day-time E-region electron density (Ne). Merging radio occultation (RO) data from the COSMIC-2 mission, the Spire RO mission and the FengYun-3 satellites showed a 30% reduction in day-time E-region Ne over mid-latitudes. The Thermosphere Ionosphere Electrodynamics – General Circulation Model (TIE-GCM) simulates this reduction albeit at a weaker magnitude. Model diagnostics show that the geomagnetic storm generated a lower thermospheric circulation that pushed air with low molecular oxygen density down into the E-region which lowered the production of Ne thereby reducing day-time Ne values. This suggests that a severe geomagnetic storm can suppress an important E-region formation mechanism.