Significant Mid- and Low-Latitude Ionospheric Disturbances Characterized by Dynamic EIA, EPBs, and SED Variations During the 13-14 March 2022 Geomagnetic Storm

This work investigates mid-and low-latitude ionospheric disturbances over the American sector during a moderate but geo-effective geomagnetic storm on 13-14 March 2022 (pi-Day storm), using ground-based Global Navigation Satellite System total electron content data, ionosonde observations, and space-borne measurements from the Global-scale Observations of Limb and Disk (GOLD), Swarm, the Defense Meteorological Satellite Program (DMSP), and the Ionospheric Connection Explorer (ICON) satellites. Our results show that this modest but geo-effective storm created a number of large ionospheric disturbances, especially the dynamic multi-scale electron density gradient features in the storm main phase as follows: (a) The low-latitude equatorial ionization anomaly (EIA) exhibited a dramatic storm-time deformation and reformation, where the EIA crests evolved into a bright equatorial band for 1-2 hr and then quickly separated back into the typical double-crest structure with a broad crest width and deep equatorial trough. (b) Strong equatorial plasma bubbles (EPBs) occurred with an abnormally high latitude/altitude extension, reaching the geomagnetic latitude of similar to 30 degrees, corresponding to an Apex height of 2,600 km above the dip equator. (c) The midlatitude ionosphere experienced a conspicuous storm-enhanced density (SED) plume structure associated with the subauroral polarization stream (SAPS). This SED/SAPS feature showed an unusual temporal variation that intensified and diminished twice. These distinct mid-and low-latitude ionospheric disturbances could be attributed to the storm-time electrodynamic effect of electric field perturbation, along with contributions from neutral dynamics and thermospheric composition change.