Ionospheric observations and modelling results over the African-European sector during the 23-25 March 2023 geomagnetic storm

We present results of ionospheric changes during the March 23-24, 2023 geomagnetic storm using observational and modelling data over the African-European sector. This paper investigates the effect of the storm main phase's "slowing down" by about 3 h due to the impact of the decreased solar wind dynamic pressure on ionospheric electron density in low latitudes. Ionosonde and Swarm observational results show that mid latitudes were characterised by negative storm effects which have been partly attributed to thermospheric composition changes. We investigate the capability of the models in reproducing the long-lived negative storm effect during the main and recovery phases over mid-latitudes in northern and southern hemispheres. Considered models were Thermosphere Ionosphere Electrodynamics General Circulation Model (TIE-GCM) and the three-dimensional storm time empirical model (3D-NNstorm) constructed based on radio occultation and ionosonde data. In terms of correlation coefficient values, TIE-GCM and 3D-NNstorm models' performance in estimating maximum electron density of the F2 layer (NmF2) ranged between similar to 0.48-0.64 and 0.64-0.88, respectively, with lower performance observed at low latitudes for both models. In response to the sudden drop in solar wind dynamic pressure that impacted the Earth's magnetosphere at 1440 UT during the storm main-phase on 23 March 2023, we show that the low-latitude ionosphere experienced a decrease in total electron content (TEC) for over 2 h which may likely be due to the reversal of electric field from eastward to westward that led to downward vertical E & times; B drift.