The effects of the May 2024 Mother’s Day superstorm over the Mediterranean sector: from data to public communication

On 8 May 2024, the solar active region AR13664 started producing a series of solar X flares and releasing multiple Interplanetary Coronal Mass Ejections (ICMEs) that proved to be geoeffective.The resulting geomagnetic storm had its Storm Sudden Commencement (SSC) on 10 May 2024 and it is, to date, the strongest since the November 2003 geomagnetic storm.The May 2024 storm, named hereafter Mother's Day storm, peaked at a Dst of -412 nT and stands out as a "standard candle" for storms affecting the modern era technologies prone to Space Weather threats.Moreover, the recovery phase showed almost no signatures of substorms, making Mother's Day storm as a perfect example of storm.Despite the plethora of interesting modifications to the near-Earth environment that are still under investigation, in this paper we concentrate on the Space Weather effects over the Mediterranean sector, with a focus on Italy.In fact, the Istituto Nazionale di Geofisica e Vulcanologia manages in the Mediterranean area dense network of GNSS receivers (including scintillation receivers), ionosondes and magnetometers, which allows for a detailed characterization of the modifications induced by the storm.Concerning the geomagnetic field, observatories located in Italy recorded a SSC with a rise time of only 3 minutes and a maximum variation of around 600 nT.The most notable effect observed in the ionosphere over the Mediterranean is a significant decrease in plasma density on 11 May following the arrival of the disturbance, resulting in a pronounced negative ionospheric storm visible on both fo F2 and Total Electron Content.Another negative effect is recorded on 13 May, while no signatures of positive storm phases are to be reported.These ionospheric negative phases are to be most likely ascribed to the effect of the neutral equatorward meridional winds resulting in a decrease of the [O]/[N 2 ] ratio.The IRI UP IONORING data-assimilation procedure, recently developed to nowcast the critical frequency fo F2 of the F2 layer over Italy, proved to be rather reliable for this extreme event, being characterised just by an overestimation during the main phase of the storm, when the electron density and the height of the F region, respectively, decreased increased significantly.Relevant outcomes of the work include findings related to the Rate of TEC change Index (ROTI), which shows high and unusual spatially distributed values on the nights of 10 and 11 May.The ROTI enhancements on 10 May might be linked