Extreme Space Weather Events Research Articles

Do the Vertical Movements of the Peak Height of F Region Truly Represent the Vertical E×B $\mathbf{E}\times \mathbf{B}$ Plasma Drift Velocity Over the Dip Equator?

AbstractThis study examines the reasons for the difference observed between the plasma drift and the drift calculated by tracing the movement of the ionospheric region peak, using a quasitwo‐dimensional theoretical ionospheric model. Analysis shows that vertical drift causes the electron density profiles in the region to steepen, where photochemistry dominates, and pushes the plasma to higher altitudes. Photochemical processes result in the lower peak , while the upper peak is attributed to vertical drift, which is difficult to trace due to diffusion effects. The close agreement between model‐derived and Scherliess‐Fejer (SF) vertical drifts confirms that the peak does not respond to vertical drift if it is below 300 km. Significant observational evidence of this phenomenon was recorded during the superstorm period of 10–11 May 2024 (Mother's Day solar storm). This superstorm period caused an increased vertical drift in the F region, leading the peak to rise above 300 km. The extreme conditions during this superstorm provided a rare opportunity to observe the dynamics of the ionosphere and validate our model. The observations during the superstorm period highlight the importance of understanding vertical drift dynamics and their impact on ionospheric behavior, especially during extreme space weather events.

Extreme Space Weather Impacts on GNSS Timing Signals for Electricity Grid Management

AbstractExtreme space weather events can have serious impacts on critical infrastructure, including Global Navigation Satellite Systems (GNSS). The use of GNSS, particularly as sources of accurate timing signals, is becoming more widespread, with one example being the measurement of electricity grid frequency and phase information to aid grid management and stability. Understanding the likelihood of extreme space weather impacts on GNSS timing signals is therefore becoming vital to maintain national electricity grid resilience. This study determines critical intensity thresholds above which the complete failure of a GNSS based timing system may occur. Solar radio bursts are identified as a simple example to investigate in more detail. The probability of occurrence of an extreme space weather event with an intensity equal to or greater than the critical intensity is estimated. Both a power law and extreme value theory were used to evaluate recurrence probabilities based on historical event frequencies. The probability was estimated to be between 3%–12% per decade to cause the complete failure of any GNSS‐based timing system.

May 11–12 Extreme Space Weather Events Brief and Dose Rate Model Response

In this brief paper, we analyze space weather events that occurred on May 11 and 12, 2024, from the perspective of an operational space weather center that provides advisories for civil aviation. One of the key metrics monitored by the center is the radiation dose rate at operational flight altitudes. A model implemented by the center provides the dose rate in real time. The model showed that dangerous levels were momentarily exceeded just above the usual 30,000 feet level during the events. This paper highlights differences in models used by various space weather centers, emphasizing the need for harmonization.

Observational Overview of the May 2024 G5-Level Geomagnetic Storm: From Solar Eruptions to Terrestrial Consequences

This study reports comprehensive observations for the G5-level geomagnetic storm that occurred from May 10 to 12, 2024, the most intense event since the 2003 Halloween storm. The storm was triggered by a series of coronal mass ejections (CMEs) originating from the merging of two active regions 13664/13668, which formed a large and complex photospheric magnetic configuration and produced X-class flares in early May 2024. Among the events, the most significant CME, driven by an X2.2 flare on May 9, caught up with and merged with a preceding slower CME associated with an X-class flare on May 8. These combined CMEs reached 1 AU simultaneously, resulting in an extreme geomagnetic storm. Geostationary satellite observations revealed changes in Earth’s magnetosphere due to solar wind impacts, increased fluxes of high-energy particles, and periodic magnetic field fluctuations accompanied by particle injections. Extreme geomagnetic storms resulting from the interaction of the solar wind with the Earth’s magnetosphere caused significant energy influx into Earth’s upper atmosphere over the polar regions, leading to thermospheric heating and changes in the global atmospheric composition and ionosphere. As part of this global disturbance, significant disruptions were also observed in the East Asian sector, including the Korean Peninsula. Ground-based observations show strong negative storm effects in the ionosphere, which are associated with thermospheric heating and resulting in decreases in the oxygen-to-nitrogen ratio (O/N2) in high-latitude regions. Global responses of storm-time prompt penetration electric fields were also observed from magnetometers over the East-Asian longitudinal sector. We also briefly report storm-time responses of aurora and cosmic rays using all-sky cameras and neutron monitors operated by the Korea Astronomy and Space Science Institute (KASI). The extensive observations of the G5-level storm offer crucial insights into Sun-Earth interactions during extreme space weather events and may help establish better preparation for future space weather challenges.

Unusual Forbush Decreases and Geomagnetic Storms on 24 March, 2024 and 11 May, 2024

As the current solar cycle 25 progresses and moves towards solar maxima, solar activity is increasing and extreme space weather events are taking place. Two severe geomagnetic storms accompanied by two large Forbush decreases in galactic cosmic ray intensity were recorded in March and May, 2024. More precisely, on 24 March 2024, a G4 (according to the NOAA Space Weather Scale for Geomagnetic Storms) geomagnetic storm was registered, with the corresponding geomagnetic indices Kp and Dst equal to 8 and −130 nT, respectively. On the same day, the majority of ground-based neutron monitor stations recorded an unusual Forbush decrease. This event stands out from a typical Forbush decrease because of its high amplitude decrease phase and rapid recovery phase, i.e., 15% decrease and an extremely rapid recovery of 10% within 1.5 h, as recorded at the Oulu neutron monitor station. Furthermore, on 10–13 May 2024, an unusual G5 geomagnetic storm (geomagnetic indices Kp = 9 and Dst = −412 nT) was registered (the last G5 storm had been observed in 2003). In addition, the polar neutron monitor stations recorded a Ground Level Enhancement (GLE74) during the recovery phase of a large Forbush decrease of 15%, which started on 10 May 2024. In this study, a detailed analysis of these two severe events in regard to the accompanying solar activity, interplanetary conditions and solar energetic particle events is provided. Moreover, the results of the NKUA “GLE Alert++ system”, the NKUA/IZMIRAN “FD Precursory Signals” method and the NKUA “ap Prediction tool” concerning these events are presented.

Modeling of Nitric Oxide Infrared radiative flux in lower thermosphere: A machine learning perspective

Nitric Oxide (NO) significantly impacts energy distribution and chemical processes in the mesosphere and lower thermosphere (MLT). During geomagnetic storms, a substantial influx of energy in the thermosphere leads to an increase in NO infrared emissions. Accurately predicting the radiative flux of Nitric Oxide is crucial for understanding the thermospheric energy budget, particularly during extreme space weather events. With advancements in computational techniques, machine learning (ML) has become a highly effective tool for space weather forecasting. This effort becomes even more worthwhile considering the availability of two decades of continuous NO infrared emissions measurement by TIMED/SABER along with several other key thermospheric variables. We present the scheme of development of an ML-based predictive model for Nitric Oxide Infrared Radiative Flux (NOIRF). Various ML algorithms have been tested for better predictive ability, and an optimized model (NOEMLM) has been developed for the study of NOIRF. This model is able to extract the underlying relationships between the input features and effectively predict the NOIRF. The NOEMLM predictions have very good agreements with SABER observation during quiet time as well as geomagnetic storms. In comparison with the existing TIEGCM model, NOEMLM has very good performance, especially during extreme space weather conditions. The results of this study suggest that utilizing geomagnetic and space weather indices with ML/AI can serve as superior parameters for studying the upper atmosphere, as compared to focusing on specific species having complex chemical processes and associated uncertainties in constituents. ML techniques can effectively carry out the analysis with greater ease than traditional chemical studies.

Daily geomagnetic variations under variable IMF/solar conditions and their connection with underground conductivity changes in Japan

Fluctuations in Solar Wind (SW) and Interplanetary Magnetic Field (IMF) significantly affect the Geomagnetic Field (GF) measurements particularly during extreme space weather events. The current study investigates the variations of horizontal (H), vertical (Z) geomagnetic components under quiet and disturbed IMF and solar conditions as well as the effect of underground conductivity on the stationary geomagnetic measurements in Japan. Results of data analysis show that the response of the GF to IMF and solar parameters fluctuations is variable. The H- and Z-components were in good harmony with high visual correlation along a latitudinal profile across Japan during quiet times. On the other hand, during the disturbed times related to a Coronal Mass Ejection (CME) launched on 13 May 2005, the GF components varied with the disturbance of IMF and solar parameters. The H-components showed highly correlated variations with a significant reduction along the examined profile due to intensified ionospheric currents, while the Z-components recorded in the northern part of Japan showed abnormal daily variations pattern (positive daily variations) with an enhanced amplitude which is opposite to the normal behavior of daily variations recorded in the central and southern parts of Japan (negative daily variations). The observed enhanced and abnormal daily variation of Z-components in north Japan, which we consider a remarkable observation here, is possibly linked with underground conductivity anomaly in this region.

An Extreme Auroral Electrojet Spike During 2023 April 24th Storm

AbstractAbrupt variations of auroral electrojets can induce geomagnetically induced currents, and the ability to model and forecast them is a pressing goal of space weather research. We report an auroral electrojet spike event that is extreme in magnitude, explosive in nature, and global in spatial extent that occurred on 24 April 2023. The event serves as a fundamental test of our understanding of the response of the geospace system to solar wind dynamics. Our results illustrate new and important characteristics that are drastically different from existing knowledge. Most important findings include (a) the event was only of ∼5‐min duration and was limited to a narrow (2°–3°) band of diffuse aurora; (b) the longitudinal span covered the entire nightside sector, possibly extending to the dayside; (c) the trigger seems to be a transient solar wind dynamic pressure pulse. In comparison, substorms usually last 1–2 hr and span almost the entire latitudinal width of the auroral oval. Magnetic perturbation events (MPEs) span hundreds km in radius. Both substorms and MPEs are mainly driven by disturbances in the magnetotail. A possible explanation is that the pressure pulse compresses the magnetosphere and enhances diffuse precipitation of electrons and protons from the inner plasma sheet, which elevates the ionospheric conductivity and intensifies the auroral electrojet. Therefore, the event exhibits a potentially new type of geomagnetic disturbance and highlights a solar wind driver that is enormously influential in driving extreme space weather events.

Prediction of ionospheric total electron content over low latitude region: Case study in Ethiopia

This study mainly focuses on the prediction of the variability of the Total Electron Content (TEC) affecting space and ground-based technological infrastructures vulnerable to extreme space weather events. The impact of solar wind conditions (SWC) can be quantified by measuring the ionosphere’s TEC. We used a machine learning (ML) algorithm based on the Support Vector Machine (SVM), Long Short-Term Memory (LSTM) Neural Network (NN), and International Reference Ionosphere 2016 (IRI 2016) models to predict the hourly TEC over Ethiopia during quiet and storm geomagnetic conditions. We considered TEC data from the Global Positioning System (GPS) stations at ADIS, CURG, and NEGE during the years 2013 to 2016. The results indicated that the SVM model predicted the hourly TEC variation with a root mean square error (RMSE) between 2.136 and 7.923 Total Electron Content Unit (TECU) under different ionospheric conditions. For the LSTM model, the RMSE between the predicted and observed TEC lies between 1.483 and 2.527 TECU. But the empirical IRI 2016 models’ RMSE from GPS TEC is in the range of 4.777 and 14.519 TECU. The statistical study points out the LSTM has the highest prediction accuracy and is the most robust for accurate prediction of ionospheric TEC in comparison to the SVM and IRI 2016 models throughout both storm and quiet periods. The result can be further improved with a lower RMSE (high correlation) by utilizing auxiliary data and increasing the number of stations employed in the study. This research adds fresh insights to deep learning applications in space weather forecasting in the region of interest.

Identification and extraction of type II and III radio bursts based on YOLOv7

Solar radio bursts (SRBs) are extreme space weather events characterized by intense solar radio emissions that are closely related to solar flares. They represent signatures of the same underlying processes that are responsible for well-documented solar phenomena such as sunspots, solar flares, and coronal mass ejections (CMEs). The study of SRBs holds significant importance as it provides a means to monitor and predict solar flares and CMEs, enhancing our ability to forecast potential impacts on Earth’s communications and satellites. Typically, SRBs below several hundred megahertz can be categorized into five types (I–V), with type II and type III bursts being the most prevalent. This study introduces a novel approach based on the YOLOv7 model for the detection and classification of type II and type III SRBs. The proposed method effectively identifies and classifies various SRB types, achieving a mean average precision accuracy of 73.5%. A trained neural network was deployed for SRB detection in the Chashan Broadband Solar radio spectrograph at meter wavelength (CBSm) data, enabling the extraction of valuable SRB information for subsequent research. This demonstrates that even when we are dealing with extensive datasets, this method can automatically recognize outbursts and extract pertinent physical information. Although our experiments with the CBSm dataset currently rely on the daily spectrum, further advancements in CBSm backend data processing techniques are expected to enable near-real-time burst detection, which is a powerful tool for accurately assessing and analyzing SRBs, and significantly contribute to the field of space weather forecasting and protective measures. Furthermore, the applicability of this method to other stations within the Chinese Meridian Project II (e.g., Mingantu Spectral Radioheliograph and Daocheng Solar Radio Telescope) enhances the capability of space weather data fusion and model development. Therefore, this research represents a substantial contribution to the domain of space weather research, offering a valuable tool for the detection and classification of SRBs and thereby improving our ability to predict and mitigate the impacts of extreme space weather events on Earth’s technology and infrastructure.

Modelling electrified railway signalling misoperations during extreme space weather events in the UK

Space weather has the potential to impact ground-based technologies on Earth, affecting many systems including railway signalling. This study uses a recently developed model to analyse the impact of geomagnetically induced currents on railway signalling systems in the United Kingdom during the March 1989 and October 2003 geomagnetic storms. The March 1989 storm is also scaled to estimate a 1-in-100 year and a 1-in-200 year extreme storm. Both the Glasgow to Edinburgh line, and the Preston to Lancaster section of the West Coast Main Line are modelled. No “right side” failures (when unoccupied sections appear occupied) are suggested to have occurred during either storm, and the total number of potential “wrong side” failures (when occupied sections appear clear) is low. However, the modelling indicates “right side” and “wrong side” failures are possible on both routes during the 1-in-100 year and 1-in-200 year extreme storms, with the Glasgow to Edinburgh line showing more total misoperations than the Preston to Lancaster section of the West Coast Main Line. A 1-in-100 year or 1-in-200 year extreme storm would result in misoperations over an extended period of time, with most occurring over a duration of 2–3 h either side of the peak of the storm.

Robust and Autonomous Space Weather Charge Mitigation Coatings

National Space Weather Strategy and Action plan calls for the need to enhanceProtection of National Security, Homeland Security, and Commercial Assets and Operations against Effects of Space Weather. Extreme space weather event like solar flares, cosmic rays, and radiation belts cause ionizing radiation that can damage electronics, solar arrays, and optical systems on satellites reducing their functionality and lifetimes, by inducing an ionic charge on the spacecraft’s surface, when a spacecraft fly in and out of the ionosphere. This negative charge buildup can lead to ion sputtering/arcing, and producing irreparable damage in spacecraft components. Therefore, the local application of materials systems that can passively mitigate the negative charge build up by emitting the electron back into space, while improving resistance to erosion during ion sputtering is of interest. Accordingly, Faraday Technology is developing a low-cost, efficient and scalable manufacturing process for the local deposition of lightweight passive highly emissive and erosion resistant coating onto spacecraft viable substrates that can mitigate charging and erosion effects from ionizing radiation. The composite coating showed a ~1500% increase in maximum (Emax) total electron yield over bare aluminum, extending by 4 times the range of electron yields between crossover energies >1, and demonstrated the potential for erosion resilience in modeled International Space Station plasma erosion conditions. The composite coating could be applied to various spacecraft platforms include spacecraft skin, solar arrays, circuit boards, and emitters such that their lifetime, effectiveness and durability within LEO/GEO environments events can be enhanced. Acknowledgements:The financial support of NASA SBIR/STTR program through contract No.80NSSC22PB020 is acknowledged.

The Extreme Space Weather Event of 1872 February: Sunspots, Magnetic Disturbance, and Auroral Displays

We review observations of solar activity, geomagnetic variation, and auroral visibility for the extreme geomagnetic storm on 1872 February 4. The extreme storm (referred to here as the Chapman–Silverman storm) apparently originated from a complex active region of moderate area (≈ 500 μsh) that was favorably situated near disk center (S19° E05°). There is circumstantial evidence for an eruption from this region at 9–10 UT on 1872 February 3, based on the location, complexity, and evolution of the region, and on reports of prominence activations, which yields a plausible transit time of ≈29 hr to Earth. Magnetograms show that the storm began with a sudden commencement at ≈14:27 UT and allow a minimum Dst estimate of ≤ −834 nT. Overhead aurorae were credibly reported at Jacobabad (British India) and Shanghai (China), both at 19.°9 in magnetic latitude (MLAT) and 24.°2 in invariant latitude (ILAT). Auroral visibility was reported from 13 locations with MLAT below ∣20∣° for the 1872 storm (ranging from ∣10.°0∣–∣19.°9∣ MLAT) versus one each for the 1859 storm (∣17.°3∣ MLAT) and the 1921 storm (∣16.°2∣ MLAT). The auroral extension and conservative storm intensity indicate a magnetic storm of comparable strength to the extreme storms of 1859 September (25.°1 ± 0.°5 ILAT and −949 ± 31 nT) and 1921 May (27.°1 ILAT and −907 ± 132 nT), which places the 1872 storm among the three largest magnetic storms yet observed.

Impacts of Extreme Space Weather Events on September 6th, 2017 on Ionosphere and Primary Cosmic Rays

The strongest X-class solar flare (SF) event in 24th solar cycle, X9.3, occurred on 6 September 2017, accompanied by earthward-directed coronal mass ejections (CMEs). Such space weather episodes are known to cause various threats to human activities ranging from radio communication and navigation disturbances including wave blackout to producing geomagnetic storms of different intensities. In this study, SFs’ ionospheric impacts and effects of accompanied heliospheric disturbances on primary cosmic rays (CR) are investigated. This work offers the first detailed investigation of characteristics of these extreme events since they were inspected both from the perspective of their electromagnetic nature, through very low frequency (VLF) radio waves, and their corpuscular nature of CR by multi-instrumental approach. Aside data recorded by Belgrade VLF and CR stations, data from GOES and SOHO space probes were used for modeling and analysis. Conducted numerical simulations revealed a significant change of ionospheric parameters (sharpness and effective reflection height) and few orders of magnitude increase of electron density. We compared our findings with those existing in the literature regarding the ionospheric response and corresponding parameters. In addition, Forbush decrease (FD) magnitude, corrected for magnetospheric effect, derived from measurements, and one predicted from power exponents used to parametrize the shape of energetic proton fluence spectra at L1 were compared and found to be in good agreement. Presented findings could be useful for investigation of atmospheric plasma properties, particles’ modeling, and prediction of extreme weather impacts on human activities.

Extreme Event Statistics in Dst, SYM‐H, and SMR Geomagnetic Indices

AbstractExtreme space weather events are rare, and quantifying their likelihood is challenging, often relying on geomagnetic indices obtained from ground‐based magnetometer observations that span multiple solar cycles. The Dst index ring‐current monitor, derived from an hourly average over four low‐latitude stations, is a benchmark for extreme space weather events, and has been extensively studied statistically. We apply extreme value theory (EVT) to two geomagnetic ring current indices: SYM‐H (derived from 6 stations) and SMR (derived from up to 120 stations). EVT analysis reveals a divergence between the return level found for Dst, and those for SYM‐H and SMR, that increases non‐linearly with return period. For return periods below 10 years, hourly averaged SYM‐H and SMR have return levels similar to Dst, but at return periods of 50 and 100 years, they respectively exceed that of Dst by about 10% and 15% (SYM‐H) and about 7% and 12% (SMR). One minute resolution SYM‐H and SMR return levels progressively exceed that of Dst; their 5, 10, 50, and 100 year return levels exceed that of Dst by about 10%, 12%, 20% and 25% respectively. Our results indicate that consideration should be given to the differences between the indices if selecting one to use as a bench mark in model validation or resilience planning for the wide range of space weather sensitive systems that underpin our society.

Auroral oval reconstruction for historical geomagnetic storms in the 18th and 19th century

AbstractThe investigation of extreme space weather events can yield important information about the solar activity. Here, we present the reconstruction of the auroral oval position and size based on Bayesian inference for nine historical geomagnetic storms between 1716 and 1882, including the Carrington event in 1859, by using ground‐based observations, which enables us to derive the Kp index for historical events for the first time. The results for the latter show a very high level of geomagnetic disturbance (8.2 Kp 8.7, −929 nT Dst −1327 nT). Furthermore, we were able to derive the position of the pole in corrected geomagnetic coordinates, where especially the longitude is in good agreement with the position derived from the gufm1 model (Jackson et al., 2000). For the eight other historical storms, the Kp and Dst indices have been calculated here for the first time. In all cases, a very high Kp index was derived. The only exception is the geomagnetic storm from March 1716, which is, with a Kp index of , comparable with the St. Patrick's Day storm in 2015.

Climatological predictions of the auroral zone locations driven by moderate and severe space weather events

Auroral zones are regions where, in an average sense, aurorae due to solar activity are most likely spotted. Their shape and, similarly, the geographical locations most vulnerable to extreme space weather events (which we term ‘danger zones’) are modulated by Earth’s time-dependent internal magnetic field whose structure changes on yearly to decadal timescales. Strategies for mitigating ground-based space weather impacts over the next few decades can benefit from accurate forecasts of this evolution. Existing auroral zone forecasts use simplified assumptions of geomagnetic field variations. By harnessing the capability of modern geomagnetic field forecasts based on the dynamics of Earth’s core we estimate the evolution of the auroral zones and of the danger zones over the next 50 years. Our results predict that space-weather related risk will not change significantly in Europe, Australia and New Zealand. Mid-to-high latitude cities such as Edinburgh, Copenhagen and Dunedin will remain in high-risk regions. However, northward change of the auroral and danger zones over North America will likely cause urban centres such as Edmonton and Labrador City to be exposed by 2070 to the potential impact of severe solar activity.

Ionospheric and magnetic signatures of extreme space weather events of 17 March and 23 June 2015 over the African sector

We have investigated responses of the African sector of the ionosphere to 17 March and 23 June 2015 severe geomagnetic storms. The vertical total electron content (TEC) measurements from Global Navigation Satellite System (GNSS) stations, which are located across the African continent, have been used to estimate the deviation of TEC (ΔTEC). The observed ionospheric response to these events was different at different locations. In the main phase of the 17 march 2015 storm, a significant positive ionospheric storm (ΔTEC maximum) occurred at Meli (245.8% enhancement) and Adis (105% enhancement) stations in the post-sunset period. On the other hand, during midnight negative ionospheric storms (ΔTEC minimum: ∼ 46%–68% depletion ) were observed at Dakr, Nklg, Wind, and Haro stations. The effects of 23 June 2015 storm are more pronounced during the initial phase. In the recovery phase of 23 June storm, negative storm effects observed at the eastern dip latitude and western equatorial stations. In contrast, at the northern and southern mid-latitude stations, we observed positive storm effect during the night periods. Night time TEC enhancement at mid-latitude stations probably caused by the vertical drift of the ionospheric plasma. We have also studied the magnetic signatures of the severe storms of 17 March and 23 June 2015 by analyzing their impacts on the horizontal (H-component) of the Earth’s magnetic field. By using a moving average filter, we have separated the effect of the magnetic disturbance (DP2) and the disturbance dynamo (Ddyn). The H-component analysis shows that there was maximum oscillation of DP2 and Ddyn currents occurrence when the IMF-Bz directed southward. In the main and recovery phases of the storm, this strong current oscillation is the driver for the development of positive ionospheric effect.

Space Weather: From solar origins to risks and hazards evolving in time

Space Weather is the portion of space physics that has a direct effect on humankind. Space Weather is an old branch of space physics that originates back to 1808 with the publication of a paper by the great naturalist Alexander von Humboldt (Von Humboldt, Ann. Phys. 1808, 29, 425–429), first defining a “Magnetische Ungewitter” or magnetic storm from auroral observations from his home in Berlin, Germany. Space Weather is currently experiencing explosive growth, because its effects on human technologies have become more and more diverse. Space Weather is due to the variability of solar processes that cause interplanetary, magnetospheric, ionospheric, atmospheric and ground level effects. Space Weather can at times have strong impacts on technological systems and human health. The threats and risks are not hypothetical, and in the event of extreme Space Weather events the consequences could be quite severe for humankind. The purpose of the review is to give a brief overall view of the full chain of physical processes responsible for Space Weather risks and hazards, tracing them from solar origins to effects and impacts in interplanetary space, in the Earth’s magnetosphere and ionosphere and at the ground. In addition, the paper shows that the risks associated with Space Weather have not been constant over time; they have evolved as our society becomes more and more technologically advanced. The paper begins with a brief introduction to the Carrington event, arguably the greatest geomagnetic storm in recorded history. Next, the descriptions of the strongest known Space Weather processes are reviewed, tracing them from their solar origins. The concepts of geomagnetic storms and substorms are briefly introduced. The main effects/impacts of Space Weather are also considered, including geomagnetically induced currents (GICs) which are thought to cause power outages. The effects of radiation on avionics and human health, ionospheric effects and impacts, and thermosphere effects and satellite drag will also be discussed. Finally, we will discuss the current challenges of Space Weather forecasting and examine some of the worst-case scenarios.

N-S Asymmetry and Solar Cycle Distribution of Superactive Regions from 1976 to 2017

There were 51 superactive regions (SARs) during solar cycles (SCs) 21–24. We divided the SARs into SARs1, which produced extreme space weather events including ≥X5.0 flares, ground level events (GLEs), and super geomagnetic storms (SGSs, Dst < −250 nT), and SARs2, which did not produce extreme space weather events. The total number of SARs1 and SARs2 are 31 and 20, respectively. The statistical results showed that 35.5%, 64.5%, and 77.4% of the SARs1 appeared in the ascending phase, descending phase, and in the period from two years before to the three years after the solar maximum, respectively, whereas 50%, 50%, and 100% of the SARs2 appeared in the ascending phase, descending phase, and in the period from two years before to the three years after the solar maximum, respectively. The total number of SARs during an SC has a good association with the SC amplitude, implying that an SC with a higher amplitude will have more SARs than that with a lower amplitude. However, the largest flare index of a SAR within an SC has a poor association with the SC amplitude, suggesting that a weak cycle may have a SAR that may produce a series of very strong solar flares. The analysis of the north–south asymmetry of the SARs showed that SARs1 dominated in the southern hemisphere of the sun during SCs 21–24. The SAR2 dominated in the different hemispheres by turns for different SCs. The solar flare activities caused by the SARs with source locations in the southern hemisphere of the sun were much stronger than those caused by the SARs with source locations in the northern hemisphere of the sun during SCs 21–24.