The main objective of the TechTIDE project (warning and mitigation technologies for travelling ionospheric disturbances effects) is the development of an identification and tracking system for travelling ionospheric disturbances (TIDs) which will issue warnings of electron density perturbations over large world regions. The TechTIDE project has put in operation a real-time warning system that provides the results of complementary TID detection methodologies and many potential drivers to help users assess the risks and develop mitigation techniques tailored to their applications. The TechTIDE methodologies are able to detect in real time activity caused by both large-scale and medium-scale TIDs and characterize background conditions and external drivers, as an additional information required by the users to assess the criticality of the ongoing disturbances in real time. TechTIDE methodologies are based on the exploitation of data collected in real time from Digisondes, Global Navigation Satellite System (GNSS) receivers and Continuous Doppler Sounding System (CDSS) networks. The results are obtained and provided to users in real time. The paper presents the achievements of the project and discusses the challenges faced in the development of the final TechTIDE warning system.

Traveling ionospheric disturbances (TIDs) are the ionospheric signatures of atmospheric gravity waves. Their identification and tracking is important because the TIDs affect all services that rely on predictable ionospheric radio wave propagation. Although various techniques have been proposed to measure TID characteristics, their real‐time implementation still has several difficulties. In this contribution, we present a new technique, based on the analysis of oblique Digisonde‐to‐Digisonde “skymap” observations, to directly identify TIDs and specify the TID wave parameters based on the measurement of angle of arrival, Doppler frequency, and time of flight of ionospherically reflected high‐frequency radio pulses. The technique has been implemented for the first time for the Network for TID Exploration project with data streaming from the network of European Digisonde DPS4D observatories. The performance is demonstrated during a period of moderate auroral activity, assessing its consistency with independent measurements such as data from auroral magnetometers and electron density perturbations from Digisondes and Global Navigation Satellite System stations. Given that the different types of measurements used for this assessment were not made at exactly the same time and location, and that there was insufficient coverage in the area between the atmospheric gravity wave sources and the measurement locations, we can only consider our interpretation as plausible and indicative for the reliability of the extracted TID characteristics. In the framework of the new TechTIDE project (European Commission H2020), a retrospective analysis of the Network for TID Exploration results in comparison with those extracted from Global Navigation Satellite System total electron content‐based methodologies is currently being attempted, and the results will be the objective of a follow‐up paper.

On 10 May 2024 at 17 h:07 UTC, the simultaneous arrival of several solar coronal mass ejections (CMEs) generated the strongest geomagnetic storm of the last twenty years, with a minimum Dst = −412 nT, usually referred to as the Mother’s Day event. On 10 October 2024, the second strongest event of solar cycle 25 appeared with a Dst = −335 nT, preceded on 8 October by an event with a Dst = −153 nT. In the present work, with measurements of the vertical total electron content and with ionosonde observations from Europe, USA, and South Korea, we show that the ionization of the upper atmosphere shortly increased at the arrival of the CME for these different events, followed by a fast decrease at all latitudes. The ionization remained very low for more than a full day. While the recovery started at the beginning of the second day after the onset for both events in October, the sudden recovery in the middle of the second day on 12 May is much more unusual. The analysis of the observations at different latitudes and longitudes shows that the causes of the ionization variations during the superstorms were mainly due to strong perturbations in the ionospheric F layer, amplified by the plasmasphere’s influence on the vertical total electron content (VTEC). The erosion of the plasmasphere during these two strong events led to a plasmapause located at exceptionally low radial distances smaller than 2 Re (Earth’s radii) in the post-midnight sector and a rotating plume in the afternoon–dusk sector clearly visible in the BSPM plasmasphere model. It took several days after the storms to recover normal ionization rates.

This paper presents a review on the PECASUS service, which provides advisories on enhanced space weather activity for civil aviation. The advisories are tailored according to the Standards and Recommended Practices of the International Civil Aviation Organization (ICAO). Advisories are disseminated in three impact areas: radiation levels at flight altitudes, GNSS-based navigation and positioning, and HF communication. The review, which is based on the experiences of the authors from two years of running pilot ICAO services, describes empirical models behind PECASUS products and lists ground- and space-based sensors, providing inputs for the models and 24/7 manual monitoring activities. As a concrete example of PECASUS performance, its products for a post-storm ionospheric F2-layer depression event are analyzed in more detail. As PECASUS models are particularly tailored to describe F2-layer thinning, they reproduce observations more accurately than the International Reference Ionosphere model (IRI(STORM)), but, on the other hand, it is recognized that the service performance is much affected by the coverage of its input data. Therefore, more efforts will be directed toward systematic measuring of the availability, timeliness and quality of the data provision in the next steps of the service development.

In this work, we investigate various types of ionospheric disturbances observed over Europe following the earthquake that occurred in Turkey on 6 February 2023. By combining observations from Doppler sounding systems, ionosondes, and GNSS receivers, we are able to discern different types of disturbances, propagating with different velocities and through different mechanisms. We can detect co‐seismic ionospheric disturbances close to the epicenter, as well as ionospheric signatures of acoustic waves propagating as a consequence of propagating seismic waves. Unlike the vast majority of past ionospheric co‐seismic disturbance studies that are primarily based on Total Electron Content variations, reflecting disturbances propagating around the F‐region peak, the focus of the present study is the manifestation of disturbances at different ionospheric altitudes by exploiting complementary ionospheric remote sensing techniques. This is particularly highlighted through ionospheric earthquake‐related signatures established as specific ionogram deformations known as multiple‐cusp signatures which appear as additional cusps at the base of the F‐region attributed to electron density irregularities generated by Rayleigh surface waves that generate acoustic waves propagating up to the ionosphere. Therefore this study underlines the advantage that multi‐instrument investigations offer in identifying the propagation of earthquake‐related ionospheric disturbances at different ionospheric altitudes and distances from the earthquake epicenter.

This work investigates the ionospheric response to the March 2023 geomagnetic storm over American and Asian sectors from total electron content (TEC), rate of TEC index, ionospheric heights, Swarm plasma density, radio occultation profiles of Formosat-7/Cosmic-2 (F7/C2), Fabry-Perot interferometer driven neutral winds, and E region electric field. During the storm’s main phase, post-sunset equatorial plasma bubbles (EPBs) extend to higher latitudes in the western American longitudes, showing significant longitudinal differences in the American sector. Over the Indian longitudes, suppression of post-sunset irregularities is observed, attributed to the westward prompt penetration electric field (PPEF). At the early recovery phase, the presence of post-midnight/near-sunrise EPBs till post-sunrise hours in the American sector is associated with the disturbance of dynamo-electric fields (DDEF). Additionally, a strong consistency between F7/C2 derived amplitude scintillation (S4) ≥ 0.5 and EPB occurrences is observed. Furthermore, a strong eastward electric field induced an increase in daytime TEC beyond the equatorial ionization anomaly crest in the American region, which occurred during the storm’s main phase. Both the Asian and American sectors exhibit negative ionospheric storms and inhibition of ionospheric irregularities at the recovery phase, which is dominated by the disturbance dynamo effect due to equatorward neutral winds. A slight increase in TEC in the Asian sector during the recovery phase could be explained by the combined effect of DDEF and thermospheric composition change. Overall, storm-time ionospheric variations are controlled by the combined effects of PPEF and DDEF. This study may further contribute to understanding the ionospheric responses under the influence of storm-phase and LT-dependent electric fields.