An extreme geomagnetic storm comparable to the Carrington event in 1859 could have significant impact on modern infrastructure such as power grids. A previously published simulation by Blake et al. (2021, Space Weather, doi:10.1029/2020SW002585) reconstructed the magnetic field observations at Colaba, India, during the Carrington storm and provided estimates of magnetic field variations around the world. We use these results as an input to a first-principle modelling method to estimate the geoelectric field in Fennoscandia based on a 3-dimensional ground conductivity model. We compare the results with the Oct 2003 Halloween storm, which is one of the strongest events in the past 100 years and of which spatially dense magnetometer recordings are available in North Europe. Comparison of the maximum modelled geoelectric field values in Fennoscandia indicates that a Carrington-class storm could generate electric fields 1.4-20.4 times larger than the Halloween storm did, with the Carrington to Halloween ratio having a mean of 6.7 and standard deviation of 2.7.

The temporal evolution of the three-dimensional metal ion flow (MIF) is crucial for polar sporadic E layer dynamics. Yet, until now it has not been studied in detail. Here, we present a new ionospheric model for metal ion dynamics, which incorporates electric fields and winds from a whole atmospheric model. We revealed the time-dependent three-dimensional MIFs in the polar ionosphere, driven by two-cell convective electric fields. The simulated MIFs closely matched observations reported in previous studies and were primarily caused by electric fields. For example, metal ions gather in the evening cell rather than the morning cell in the ionospheric $F$ region owing to the morning divergence and evening convergence electric fields; the narrow latitudinal metal ion concentrations appear in the pre-midnight ionospheric $E$ region owing to downward motions and vertical convergence of ions by electric fields. Our findings emphasize the critical role of electric fields in polar metal ion dynamics and provide valuable insights for interpreting past and future MIF observations in the polar ionosphere.

We investigate the dynamics of the multi-scale processes involved in the ionospheric response to a minor geomagnetic storm occurred on 14-15 January, 2022. During this storm, the LOw Frequency ARray (LOFAR), an European distributed radio telescope array, provided ionospheric measurements from the radio source Cassiopeia A, that we complemented with the ionospheric information provided by the Global Navigation Satellite System (GNSS) receivers covering the European sector. LOFAR operates in the HF/VHF band (between 30 and 250 MHz), while GNSS signals are in the L-band ([[EQUATION]] 1 Ghz), translating into the possibility to investigate the ionospheric irregularities formed in response to the storm at different spatial scales. The combined use of data from these two instruments gave us the opportunity to observe three distinct phenomena: (i) the increment of direct particles precipitation in the auroral oval, (ii) the steepening of the equator-ward edge of the ionospheric trough, and (iii) the propagation towards lower latitudes of wave-like structures having scale sizes of few km and velocity of hundreds of meters per seconds.

Understanding the long-term variability of nighttime Spread F (SF) and its drivers is crucial for improving the knowledge of ionospheric disturbances, which impact radio communication, GNSS positioning, and space weather forecasting. This study exploits the long-term ionogram dataset from the EB040 ionosonde in Spain (1955–2022) to investigate the climatology of nighttime SF and its dependence on solar activity. We analyze the diurnal, seasonal, and solar-cycle variability of both Range Spread F (RSF) and Frequency Spread F (FSF). The results reveal a strong inverse relationship between SF occurrence and solar activity, with SF maxima during solar minima. SF is confirmed as a predominantly nighttime phenomenon in western European mid-latitudes, primarily occurring between 20:00 and 05:00 UT, peaking near the solstices, with higher occurrence in June–July than in December–January, and with RSF accounting for 69% of SF events. Complementary analysis using GNSS-derived detrended Total Electron Content (d-TEC) and Rate of TEC index (ROTI) maps (2012–2016) quantifies the connection with Medium-Scale Traveling Ionospheric Disturbances (MSTIDs). Approximately 85% of SF occurrences at EB040 coincide with MSTID activity, with correlation coefficients above 0.96 between their onset times. MSTID activity exhibits the same seasonal pattern as SF, peaking at the solstices—particularly in June–July—and displaying the same inverse dependence on solar activity. Furthermore, 62% of RSF events at EB040 are associated with strong ROTI activity, especially during summer, and 83% of RSF events lasting over two hours correspond to strong ROTI activity. Overall, these findings highlight MSTIDs as the dominant electrodynamic driver of mid-latitude SF and underline the seasonal and solar activity dependencies of SF variability, providing new constraints for understanding ionospheric dynamics.

The geomagnetic storm that started on May 10th 2024, often referred to as the ”Mother’s day” or ”Gannon” storm, was the strongest storm for decades with polar lights visible across significant parts of the globe. This paper focuses on the impacts in the form of GNSS signal scintillation in the Arctic, covering the geographic area of 50 to 85°N and 160°W to 40°E. The scintillation analysis is supported by ionospheric convection data from the super dual auroral radar network (SuperDARN) and currents estimated from the measurements of multiple magnetometer arrays. Positioning performance is examined for a real-time kinematic (RTK) service in Tromsø, at ≈ 70°N. An overview of the spatial and temporal occurrence of the scintillation is presented. Scintillation was observed throughout the coverage area, in connection to the auroral oval region and a tongue of ionization. Amplitude scintillation was observed but with a lesser magnitude (S4 values up to 0.2) and extent than the phase scintillation. The connection of the scintillation to the auroral electrojets and vertical currents is examined in detail. Scintillation is found to occur within both the eastward and westward electrojets but is not a constant feature. Phase scintillation in the eastward electrojet tends to occur near the poleward boundary. Some periods of strong vertical currents are associated with scintillation. Accurate positioning services were severely degraded during the event. For many users they would be in practice unusable for up to 37 consecutive hours. To the best of our knowledge, at the time of writing this paper presents the most complete overview of high latitude scintillations during this storm, and demonstrates the value of combining data from multiple instruments for enhanced insight.

Near the peak of Solar Cycle 25 in 2024, Earth was impacted by two major solar eruptive events which triggered dramatic geomagnetic storm activity. In May 2024, multiple solar eruptive events generated the largest geomagnetic storm since the early 2000s; this was followed by a similar size geomagnetic storm in October 2024, driven by a single solar eruptive event. Both storms occurred in the `social media era' where the widespread use of mobile imaging devices on `smartphones' encouraged the public to go outside and witness the storms, often capturing and sharing photographs; examples local to the island of Ireland are analysed in this study. While the socio-historic impact of the storms was significant, in this manuscript the sources and effects of the two storms are compared and contrasted. A ``Sun-to-Mud'' analysis is presented, from the solar origins of the events down to regional electrodynamic effects over the island of Ireland. Results indicate that while the May storm was driven by a compound CME-CME event following a quiet period, the single CME driving the October storm arrived at a magnetosphere primed by previous activity. Both storms exhibit strong solar wind - magnetosphere - ionosphere coupling, and the precursor activity in October demonstrates that the time history of magnetosphere-ionosphere priming is an important factor that influences the ultimate effect of a transient solar-driven event. Locally over the island of Ireland, observations suggest auroral electrojets poleward of local magnetometers, and both events generate remarkable geomagnetically induced currents; these observations are presented along with local auroral photographs.

The May 2024 space weather disturbance is the latest (as of the time of writing) in a series of space weather events going back to 1859 that have documented impacts to critical infrastructure and technologies. Impacts to these systems range from minor degradation (e.g., static or noise in a communication link) to major, which was demonstrated by a complete blackout of the Hydro-Québec power system on 13 March 1989. This event stimulated international space weather awareness and motivated efforts toward improved resilience. This paper presents the May 2024 space weather event from a unique Canadian perspective demonstrating the Canadian Space Weather Forecast Centre (CSWFC) approach to monitoring, forecasting, and alerting to characterize space weather phenomena and mitigate their impacts. Satellite data, numerical modelling of solar wind disturbances, and ground-based magnetometer and riometer data from instruments located in Canada demonstrate the progression of the event. In response to observations of enhanced solar activity, the CSWFC issued a major geomagnetic storm WATCH spanning an almost 3-day period, a major geomagnetic storm WARNING for > 1 day that began at auroral latitudes, but quickly expanded to cover all of Canada, and a solar proton WARNING for > 2 days. Impacts to high frequency communications and Global Navigation Satellite System positioning navigation and timing over Canada are evaluated using Transport Canada’s Civil Aviation Daily Occurrence Reporting System entries and reported outages of the Wide Area Augmentation System. This paper compares the May 2024 event with the March 1989 event and evaluates the latitude and magnetic local time distribution of the geomagnetic perturbations. In general, geomagnetic activity increased from southeastern to northwestern North America.

In this contribution, we propose a new short-term forecast machine learning model of Large Scale Travelling Ionospheric Disturbances (LSTIDs) occurrence at specific locations in Europe. The model is trained using as input data time series of LSTIDs drivers and characteristics of LSTIDs detected events. The concept underpinning the selection of the input data is based on the phenomenological scenario that the intensity of the auroral electrojets is regulated by the Lorentz force and the Joule heating generates Atmospheric Gravity Waves (AGWs) in the lower thermosphere and LSTIDs in the ionosphere. Based on this scenario, the Total Electron Content (TEC) gradients and the intensity of the auroral electrojets are representative drivers for LSTIDs occurrence. Detected LSTID events and their characteristics are calculated with the HF Interferometry method (HF-INT) over European Digisonde stations. The method looks for coherent oscillation activity in the Maximum Usable Frequency for a 3000 km radio path via reflection from the F2 layer (MUF(3000)F2) , and sets bounds to time intervals for which such activity occurs into a given region. HF-INT provides the Spectral Energy Contribution (SEC), which is the contribution of the LSTIDs to the total variability for a given time series. These features (drivers and detected characteristics) are exploited for the forecast of LSTID occurrence utilizing an advanced Machine Learning tool, namely, the Temporal Fusion Transformer (TFT) model. The performance of the TFT model is compared with other more traditional classifiers, such as, the k-Nearest Neighbor classifier (k-NN), the Feedforward Neural Networks (FNNs). Several experiments are performed for two distinct scenarios: (a) values of SEC greater than 50% indicating moderate and strong LSTID activity, and (b) values of SEC greater than 70% indicating strong LSTID activity. The classifiers’ performance is assessed through the F1-score metric, which takes values between 0 and 1 (the higher its value, the better the classifier performance). The forecasting accuracy decreases from 0.9 to 0.6 approximately with increasing forecasting horizon up to two hours ahead for TFT, while the FNNs have the next best performance, and k-NN has inferior performance. The qualitative analysis of the TFT results provides evidence for a more direct dependence of the performance of the models from the historical time series of SEC at the Digisonde locations that are closer to the auroral oval, and much weaker dependence for the lower latitude Digisonde locations. This might be the result of the decreasing LSTIDs amplitude as they travel equatorward and could highlight the dissipative nature of the ionospheric medium. The TFT performance analysis leads to the conclusion that the forecast of LSTID occurrence is extremely complex as it involves not only a careful data pre-processing but also consideration of the drivers, of the propagation pattern and of other phenomena, such as the damping effect and the interhemispheric propagation.

Magnetospheric-ionospheric coupling studies often rely on multi-spacecraft conjunctions, which require accurate magnetic field mapping tools. For example, linking measurements from the magnetotail with those in the ionosphere involves determining when the orbital magnetic footpoint of THEMIS or MMS intersects with the footpoint of Swarm. The Tsyganenko models are commonly used for tracing magnetic field lines. In this study, we aim to analyze how the footpoint locations are impacted by the inputs parameters of these models, including solar wind conditions, geomagnetic activity, and the location in the magnetotail. A dataset of 2394 bursty bulk flows (BBFs) detected by MMS was mapped to Earth's ionosphere with six different Tsyganenko models. Approximately 90% of the ionospheric footpoints are concentrated within 70° +/- 5° magnetic latitude (MLAT) and +/- 3 hours of magnetic local time (MLT) around midnight, with a pronounced peak in the pre-midnight sector. The MLT position showed a difference of approximately +/- 1 hour MLT across the models. Footpoint locations were linked to the dawn-dusk position of the BBFs, with differences between models associated with variations in the interplanetary magnetic field clock angle. The MLAT values exhibited similar differences of approximately +/- 4° around the mean value, with a systematic shift toward lower latitudes in the T89 model. This position is also influenced by the input parameters of the model representing the dynamics of Earth's magnetosphere, where stronger magnetospheric activity typically corresponds to lower latitudes. The uncertainty on the BBF footpoint location impacts the number of conjunctions with Swarm. Generally, Swarm B exhibited more conjunctions than Swarm A or C in the northern hemisphere. However, when considering only Swarm-BBF conjunctions where the distance between footpoints computed with T89 and TA15n is smaller than the BBF footprint size, the number of conjunctions is reduced to less than half of the total.

Studying stream interaction regions (SIRs) from their inception and the dynamics of their development can provide insights into solar–terrestrial connections and improve space weather prediction. Some in-situ instruments on the Solar Orbiter (SolO) space mission are designed to measure solar wind (SW) and interplanetary magnetic field parameters along the entire flight path. These instruments are ideal for studying the dynamics of SIR development at heliocentric distances of 0.28–1.0 AU and with changes in heliolatitude of 0°–33°. To address the challenges of promptly identifying SIRs and predicting their arrival time on Earth, we consider using trigger events from the Radio and Plasma Wave (RPW)/SolO instrument, which are transmitted in telemetry data packages. We suggest that multiple activations of the trigger mode (SBM1 mode) in the RPW instrument over an interval of up to four hours may reflect the fine structure of large-scale events in SW. Such events can serve as markers for the spacecraft’s location within the SIR. In this regard, the 2023 analysis revealed that multiple activations of the SBM1 trigger mode throughout the day accounted for more than 50% of the total number of days when such events were recorded. Of this number, 63% were events when the trigger algorithm was triggered repeatedly within a time interval of up to four hours. A comparison of the registration times of SBM1 trigger events with the SW parameters obtained from the SWA-PAS and MAG devices showed that repeated activations of the trigger algorithm occurred at the stream interface surface when a high-speed SW stream and a formed compression region were present. We believe that high gradients of changes in SW parameters in this SIR region lead to intense fluctuations in proton density and magnetic field in SW, which triggers the trigger mode. For a numerical assessment of space weather elements, we propose analytical expressions to estimate the position of coronal holes as a potential source of high-speed streams on the solar disk relative to the moment of SIR registration by SolO instruments.