We study Jupiter’s DAM radio storms to identify the features that may correlate with solar wind and coronal mass ejections (CME). We investigate the dynamics of DAM storms and burst features, and explain them by considering MHD processes associated with Io and the presence of gas in Jupiter’s lower magnetosphere. DAM radio storms occur when plasma injected by Io or by solar wind propagating along Jupiter's magnetic field lines into the auroral zone of Jupiter’s lower magnetosphere together with low-frequency Alfvén wave. Those MHD oscillations in low magnetosphere can trigger ionization processes and create streamers, activating maser instabilities in the electron plasma. This can occur under the influence of dense solar wind and CME that penetrate to Jupiter's magnetosphere, creating high-latitude currents with non-Io radio storms, and enhancing Io-dependent sources of DAM radio emissions. We found that dynamics of development of Io-dependent and non-Io DAM radio storms have similar features and evolutionary peculiarities. That time periodicities (5 min and 20 min durations) may connected with MHD instabilities activated by Io, that modulate the current sheets system in all auroral zone. The power of Io-dependent storms is modulated by the solar wind pressure on the magnetosphere of Jupiter. On the other hand, in non-Io radio sources associated with solar plasma injections, due to the content of high-energy ions which scatter on the gas fluids, a number of specific radio bursts are formed, for example, having zebra structures on high-resolution dynamic spectra.

Abstract Changes in the thermospheric wind originating in storm‐time transients in high‐latitude Joule heating and ion circulation are effective in modifying conditions throughout Earth's upper atmosphere and ionosphere. Among the effects these drivers can produce are large‐scale gravity waves (GWs), characterized by significant wind transients that propagate away from the auroral zone, driving transient ion motion during their 1–2 hr passage. Longer period changes in mean winds can develop over the following hours to days, depending on the duration and magnitude of the high latitude heating, and also extend globally. The effectiveness of these processes in modifying the mean density of the daytime ionosphere likely depends on the extent to which these disturbances reach the daytime equatorial region and downward into the E‐region wind dynamo (below 180 km). A study of a month of observations made during the ICON mission reveals the variety of behaviors with both transient effects and longer‐term changes in mean winds. The duration of auroral inputs, as opposed to the average input over time, is identified as important to the development of dynamo‐modifying zonal disturbance winds. During geomagnetic disturbances, we find that the predictive capability of a general circulation model (TIEGCM) for meridional wind transport is good (R .8) while the storm‐time zonal wind transport is harder to predict (R .5). This study is the first of its kind, measuring winds and storm responses continuously for a month in both the daytime E‐ and F‐ regions simultaneously with 97 min cadence.

On May 10–11, 2024, one of the strongest geomagnetic storms in recent years swept across the planet. Several interplanetary coronal mass ejections (ICMEs) originated from the source active region (AR 13664), propelling solar energetic particles toward Earth. Triggered by intense solar eruptions, the storm reached a Kp index of 9 (the highest on the scale), causing a remarkable expansion of auroras visible far beyond their usual high latitudes. The unprecedented strength of the storm highlights the necessity of monitoring geomagnetic disturbances using ground-based instruments to assess the far-reaching impacts of space weather events, especially in regions well beyond the typical auroral zones. In this study, geomagnetic data from several observatories located in mid-latitudes (30°-60°N) in the Northern Hemisphere were therefore utilized to analyze the G5-level super-intense Gannon storm. These observations enable the detection of geomagnetic variations, including sudden storm commencements (SSCs), prolonged negative excursions in the Disturbance Storm-Time (Dst) index, as well as localized magnetic fluctuations indicative of intensified ionospheric currents. Additionally, the auroral electrojet strength and the asymmetric distribution of geomagnetic disturbances provide critical insights into the spatial and temporal evolution of ionospheric and magnetospheric processes during the extreme geomagnetic storm, helping to understand its impacts on mid-latitude regions. The results highlight the spatial variability and temporal synchronicity of the impacts of the storm, demonstrating the crucial role of mid-latitude observatories in capturing ionospheric and magnetospheric responses during extreme geomagnetic events.

Abstract During substorms, Earth's magnetotail undergoes rapid dipolarization, driving Earthward plasma flows that decelerate and dissipate energy upon encountering the dipole magnetic field in the nightside transition region. This region mediates the interaction between the magnetotail, inner magnetosphere, and the ionospheric auroral zone, though significant mapping uncertainties obscure the precise link and particle acceleration processes. Using data from THEMIS, TREx, and ELFIN, we analyze a storm‐time substorm on 4 September 2022, establishing a relationship, that is, not a causation, between magnetospheric and ionospheric dynamics. Following a dipolarization, the auroral bulge overlapped with the footprints of the electron isotropy boundary (IB) and the outer radiation belt. Notably, the precipitating electron energies reached at least 2 MeV in the bulge, exceeding previous reports. By comparing the latitudes of the electron IB with respect to the auroral bulge, we deduce that the sources of both auroral and relativistic precipitation were confined in the dipolarized region.

The presented work examines the extreme geomagnetic storm that occurred during May 10–12, 2024, following solar flares on May 8–9, 2024, hence named the Victory Day Storm. This event, marked as the most intense geomagnetic storm of the 21st century to date, caused significant disturbances not only in the auroral zone but also in the subauroral and mid-latitude ionosphere. Using data from satellites, ground-based ionosondes, Global Navigation Satellite System (GNSS) receivers, and all-sky cameras located in the Kaliningrad region, this research tracks how the coronal mass ejection from the Sun led to substantial changes in ionospheric plasma density, structure, and dynamics. Notably, auroras were observed in the subauroral and mid-latitudes, which is a rare phenomenon at these latitudes, providing valuable information on the ionospheric response to extreme geomagnetic activity. Swarm and DMSP satellite data identified polarization jet/SAID as U-shaped structures on ionograms, while Strong Thermal Emission Velocity Enhancements (STEVE) was observed by an all-sky camera along with increased Rate of Total Electron Content Index (ROTI). A diffuse aurora with a moving omega structure, as well as ray and corona auroral features, were observed, accompanied by a significant ROTI increase and enhanced scattering of the auroral Es layer on ionograms.

Observations from the Juno satellite have indicated very low electron densities, as low as 10^{-3} cm^{-3}, at high-latitudes in Jupiter's magnetosphere. This region is strongly magnetized, with surface magnetic fields at the one-bar level up to 20G, or 2mT, leading to the unusual situation that the electron plasma frequency is less than the ion gyrofrequency. In this extremely low-density plasma, the Alfven wave becomes a plasma oscillation at the electron plasma frequency at shorter perpendicular wavelengths. Analysis of this mode with a kinetic low-frequency dispersion solver indicates that at large wave number, this mode has the characteristics of the Langmuir wave. Thus, this mode can be called an Alfvén-Langmuir mode. Below the plasma frequency, the high-wave number behavior of this mode exhibits a resonance cone, with frequency determined by the angle of the wave vector with the background magnetic field. These waves can be excited by the upward electron beams observed by Juno.

Abstract We analyze the topside electron density and temperature during the superstorm in May 2024 (Mother's Day storm or Gannon storm), using multiple Low‐Earth Orbit (LEO) spacecraft operating at different altitudes, such as Swarm, International Space Station, Defense Meteorological Satellite Program, Polar Operational Environmental Satellites, and the Small‐scale magNetospheric and Ionospheric Plasma Experiment (SNIPE). The SNIPE mission was designed to investigate micro‐scale plasma structures in Earth's ionosphere and magnetosphere. The SNIPE constellation was launched on 25 May 2023, and continues to operate in a dawn‐dusk Sun‐synchronous orbit at an altitude of approximately 530–550 km. In this paper, we report significant changes in topside electron density and temperature, measured by SNIPE. Furthermore, SNIPE observations are compared with independent ground‐based Total Electron Content measurements and data from other LEO satellites. Three characteristics of the data are highlighted. First, we address the unusual expansion of the Equatorial Ionization Anomaly around the magnetic equator and its hemispheric asymmetry, which is dependent on altitude. Second, a large Tongue of Ionization in the polar region extends to ∼840 km above the ground, accompanied by a weak decrease in electron temperature. Third, we report electron temperature enhancement near the auroral zones across a wide range of local times, which partially overlaps with energetic particle precipitation. These three results complement existing studies of the Mother's Day/Gannon geomagnetic storm.

Abstract. The complete existing time series of K indices from Norwegian observatories in Tromsø (TRO), Dombås (DOB) and Bear Island (BJN) has been digitized. The digitized time series are continuous, spanning from 1939 (DOB) and 1947 (TRO) until 1998. Today, Tromsø Geophysical Observatory manages geomagnetic observations throughout Norway and K indices are calculated in real time with a fully automatic, in-house method. In this paper, the old hand-scaled and new automatic time series of K indices are reviewed and compared for the intervals where they overlap. Our analysis confirms that the digital K-index series is a valid continuation of the old series, at least in the auroral zone. Since 1939, three K-index derivation methods have been applied to Norwegian magnetic observatory data. These are traditional hand-scaling, the method developed by the Finnish Meteorological Institute and an in-house method. Here, we compare the tree methods. It becomes clear that each method has both strengths and weaknesses. Importantly, differences arise when calculating the quiet-day variation, especially during periods of consecutive disturbed nights at auroral latitudes. By analysis of the K-index frequency distributions for six stations in mainland Norway and on Svalbard, we find that the lower limit for K=9 of 2000 nT is too high for TRO and that for K=9 of 750 nT is possibly too low at DOB. The assumption that the variation in H is greater than that in D, which makes it possible to calculate K from the magnetic H component only, is investigated, and it is shown that the assumption is indeed only valid for auroral stations. In total, this paper presents all K indices derived from Norwegian observatories since the 1930s until today, the used derivation methods and the long historic time series as a whole, and thus it enables critical use of the indices for future scientific work. Finally, we present the complete Ak time series for the Norwegian observatories as well as a spectral analysis.

Spatial Structure of UV Microbursts in the Auroral Zone

Abstract In the present study we investigate the response of the dayside ground magnetic field to the sequence of interplanetary magnetic field (IMF) BY changes during the May 2024 geomagnetic storm. We pay particular attention to its extraordinarily large (>120 nT) and abrupt flip, and use GOES‐18 (G18) magnetic field measurements in the dayside magnetosheath as a time reference. In the dayside auroral zone, the northward magnetic component changed by as much as 4,300 nT from negative to positive indicating that the direction of the auroral electrojet changed from westward to eastward. The overall sequence was consistent with the conventional understanding of the IMF BY driving of zonal ionospheric flows and Hall currents, which is also confirmed by a global simulation conducted for this storm. Surprisingly, however, the time delay from G18 to the ground increased significantly in time. The delay was 2–3 min for a sharp BY reduction ∼30 min prior to the BY flip, but it became as long as 10 min for the zero‐crossing of the BY flip. It is suggested that the prolonged time delay reflected the travel time from G18 to the reconnection site, which sensitively depends on the final velocity at the magnetopause, that is, the inflow velocity of the magnetic reconnection. Around the BY flip, the solar wind number density transiently exceeded 100 cm−3, and should have increased further through the bow shock crossing. It is suggested that this unusually dense plasma reduced the reconnection rate, and therefore, the solar wind‐magnetosphere energy coupling due to the extraordinary IMF.

Abstract Polar cap patches are islands of enhanced plasma density formed during intervals of southward interplanetary magnetic field (IMF). The present study examines the observations of polar cap patches during sequential auroral substorms that occurred on 9 September 2011. The propagation and evolution of large‐scale polar cap patches were monitored by three SuperDARN radars (MCM, ZHO, and SYE) located in the Southern Hemisphere. During the substorm periods, MCM radar observed periodic blobs of anti‐sunward propagating HF backscatter echoes. By examining the 2‐D scan plots, there were the dawn‐dusk elongated radar patches moving across the magnetic pole and eventually merging into the nightside auroral zone. Simultaneous ZHO and SYE radars recorded consecutive ionospheric plasma blobs and moderate Doppler negative velocity near the poleward boundary of the nightside auroral oval. Coordinated GPS observations in ZHO showed pulsed increases in total electron content (TEC) and scintillations. Due to the high values in the TEC data, such radar patches are suggested to result from the transportation of high‐density plasma from the dayside sunlit ionosphere during sequential auroral substorms. The in situ observations by the DMSP satellite suggested re‐structuring of plasma patches near the poleward boundary of the auroral oval by pulsed flow bursts.

It is commonly accepted that the shape and temporal evolution of the auroral zones (here defined as the climatological average of the auroral ovals) are primarily influenced by the dipolar and high-latitude features of the geomagnetic field. Though recent studies challenge this view, a systematic approach to linking the joint evolution of auroral zones and geomagnetic field is currently missing. Here we attempt to fill this gap via the introduction of a novel technique, based on a Green's function approach, that allows exploration of the sensitivity of the auroral zones to regional changes of the internally generated magnetic field at the core-mantle-boundary (CMB). We define key diagnostics for the auroral zones shapes and location: the auroral zone surface area, the location of their centroid (i.e. their geometric centre), and the distance between the zones and selected cities. We focus on the temporal period covered by ESA's Swarm mission. We find that temporal changes in the dipolar field dominate the variation in the location of the auroral zones, i.e. their centroid latitudes and distances from selected locations. However, non-dipolar contributions play and important role, especially in the Northern Hemisphere. In particular, they dominate changes in the northern auroral zone surface area and offset the dipolar contribution to the distance from Northern England locations. Furthermore we show that all diagnostics are influenced by geomagnetic field changes that are globally distributed on the surface of the Earth's core, and not only in the polar regions. We found significant contribution from the mid-to-low latitude regions and, in particular, from the same geomagnetic features responsible for the existence of the South Atlantic Anomaly. Our methodology thus provides a link between polar and mid-to-low latitude features of interest for space weather and space climate.

Abstract Substorms have been identified from negative bays in the AL/SML index, which traces the minimum northward ground magnetic deflection at auroral latitudes, produced by enhancements of the westward electrojet. For substorms, negative bays are caused by the closure of the Substorm Current Wedge through the ionosphere, typically localized to the nightside and centered around 23‐00 magnetic local time (MLT). In this case, the equivalent current pattern that causes the magnetic deflections is given the name Disturbance Polar (DP) 1. However, negative bays may also form when the westward electrojet is enhanced by increased convection, driving Pedersen and Hall currents in the auroral zone. Convection enhancements also strengthen the eastward electrojet, monitored by AU/SMU index. In this case, the equivalent current pattern that produces the magnetic deflections is called DP2. Unlike other substorm identification methods, the Substorm Onsets and PHases from Indices of the Electrojets technique by Forsyth et al. (2015), https://doi.org/10.1002/2015ja021343 attempts to distinguish between the DP1 and DP2 enhancements that cause substorm‐like SML bays. Despite this, we find evidence that between 1997 and 2019 up to 59% of the 30,329 events originally identified as substorms come from enhancements of DP2 on top of the 2,627 convection enhancement events already identified. We explore ways to improve substorm identification using auroral indices to fully separate the DP1 and DP2 bays but conclude that there is insufficient information in the auroral indices to achieve this. In reality, any “substorm” list is a list of magnetic enhancements, auroral enhancements, etc., which may or may not correspond to substorm activity and should be treated that way.

Abstract Penetrating and disturbed electric fields develop during geomagnetic storms and are effective in driving remarkable changes in the nightside low latitude ionosphere over varying time periods. While the former arrive nearly instantaneously with the changes in the solar wind electric field, the latter take more time, requiring auroral heating to modify upper atmospheric winds globally, leading to changes in the thermospheric wind dynamo away from the auroral zones. Such changes always differ from the quiet time state where the winds are usually patterned after daytime solar heating. We use the Multiscale Atmosphere‐Geospace Environment model (MAGE) and observations from the NASA Ionospheric Connection Explorer (ICON) mission to investigate both during the 7–8 July 2022 geomagnetic storm event. The model was able to simulate the penetrating and disturbed electric fields. The simulations showed enhanced westward winds and the wind dynamo induced upward ion drift confirmed by the ICON zonal wind and ion drift observations. The simulated zonal wind variations are slightly later in arrival at the low latitudes. We also see the penetrating electric field opposes or cancels the disturbed electric field in the MAGE simulation.

The Sun showed extraordinary activity related to sunspot area 3664 on May 8–10, 2024, resulting in solar flares considered the most intense in the current solar cycle. Auroras occurred in several regions around the world. Early on May 12, 2024 near the highest peak in the Sultanate of Oman, a team of Omani astrophotography enthusiasts documented the rare event ever observed in this region. Auroras often occur along the so-called auroral oval zones around the geomagnetic poles, where Earth's magnetic field directs charged particles penetrating from the solar wind. This takes place when a cloud of charged particles is thrown toward Earth by a large explosion on the Sun. Sometimes, these particles can make the aurora visible in places where it is exceedingly rare throughout recorded history. The observation from the mountain Jebel Shams, situated far from the polar regions (23 degrees north of the equator), offers a unique chance to study such an event in a region where auroras are exceptionally rare. We explore the factors contributing to the observed aurora in Oman, including geomagnetic conditions and the role of sunspot region AR3664 in solar activity along with local conditions in Oman that contributed to the visibility of this aurora. Understanding this dynamics can enhance our knowledge of the mechanisms driving auroral visibility at lower latitudes and provide valuable insights into the global impact of solar storms. This study also emphasizes how crucial it is to record auroras in regions like the Arabian Peninsula, where they are rarely documented.

The Sun showed extraordinary activity related to sunspot area 3664 on May 8–10, 2024, resulting in solar flares considered the most intense in the current solar cycle. Auroras occurred in several regions around the world. Early on May 12, 2024 near the highest peak in the Sultanate of Oman, a team of Omani astrophotography enthusiasts documented the rare event ever observed in this region. Auroras often occur along the so-called auroral oval zones around the geomagnetic poles, where Earth's magnetic field directs charged particles penetrating from the solar wind. This takes place when a cloud of charged particles is thrown toward Earth by a large explosion on the Sun. Sometimes, these particles can make the aurora visible in places where it is exceedingly rare throughout recorded history. The observation from the mountain Jebel Shams, situated far from the polar regions (23 degrees north of the equator), offers a unique chance to study such an event in a region where auroras are exceptionally rare. We explore the factors contributing to the observed aurora in Oman, including geomagnetic conditions and the role of sunspot region AR3664 in solar activity along with local conditions in Oman that contributed to the visibility of this aurora. Understanding this dynamics can enhance our knowledge of the mechanisms driving auroral visibility at lower latitudes and provide valuable insights into the global impact of solar storms. This study also emphasizes how crucial it is to record auroras in regions like the Arabian Peninsula, where they are rarely documented.

Pc5 geomagnetic pulsations (PGPs) are ultra-low frequency (ULF) waves within the 1–7 mHz frequency band observed both in space and on the ground. PGPs offer versatile methods for studying the interaction between the magnetosphere and ionosphere in space. This study presents a comparative analysis of Pc5 pulsations observed in space and on the ground. The dataset used is the magnetic field-aligned readings obtained from the Geostationary Operational Environmental Satellite-10 (GOES-10) and ground-based magnetometer stations from the Svalbard network located in the auroral zone during solar cycle 23. Using the Empirical Mode Decomposition (EMD) method, we transformed the magnetic field time series from GOES-10 into the mean field-aligned coordinate system. PGPs were extracted from the toroidal component using a bandpass Butterworth filter. In addition, Pc5 waves were extracted from the Bx component of the ground magnetometer stations to enable effective comparison. Before conducting the comparative analysis, Pc5 events on the ground and in space were denoised using the heuristic Stein Unbiased Risk Estimate (SURE) approach with soft thresholding. Consequently, a good coherence between events from space and on the ground was observed, indicating the possibility of the same generation source. However, space-borne Pc5 events have a smaller average amplitude of 12 nT compared to Pc5 events observed on the ground, having an average amplitude of 139 nT. We attributed this difference in amplitude to the transformative mechanisms during the wave's propagation to the ground. The average percentage of occurrence of Pc5 geomagnetic pulsations observed in space was found to be 74%, and that on the ground was 92%. The percentage difference was found to be due to the spatial distribution of these waves. The integrity of the retrieved events was demonstrated by the strong correlation between the Kp index and events extracted from the ground magnetometer stations. Our results contribute significantly to the understanding of Pc5 geomagnetic pulsations within the space weather community. These findings will aid in developing forecasting and predictive models, enabling more effective studies of these waves and helping to mitigate their potential impacts on human activities and infrastructure.

Abstract The strongest geomagnetic storm in the preceding two decades occurred in May 2024. Over these years, ground‐based observational capabilities have been significantly enhanced to monitor the ionospheric weather. Notably, the newly established Sanya incoherent scatter radar (SYISR) (Yue, Wan, Ning, & Jin, 2022, https://doi.org/10.1038/s41550‐022‐01684‐1), one of the critical infrastructures of the Chinese “Meridian Project,” provides multiple parameter measurements in the upper atmosphere at low latitudes over Asian longitudies. Unique ionospheric changes on superstorm day 11 May were first recorded by the SYISR experiments and the geostationary satellite (GEO) total electron content (TEC) network over the Asian sector. The electron density or TEC displayed wavelike structures rather than a regular diurnal pattern. Surprisingly, two humps, a common feature in the daytime equatorial ionization anomaly structure, disappeared. The SYISR observations revealed that multiple wind surges accompanied the downward phase propagation caused by atmospheric gravity waves (AGWs) originating from auroral zones. Meanwhile, strong upward and large downward drifts were respectively observed in the daytime and around sunset. The Thermosphere‐Ionosphere Electrodynamics Global Circulation Model (TIEGCM) simulations demonstrated that abnormal ionospheric changes were attributed to meridional wind disturbances associated with AGWs and recurrent penetration electric fields corresponding to larger Bz southward excursions and disturbance dynamo. The complicated interplay between AGWs and disturbance electric fields contributed to this unique ionospheric variation.

Abstract Intense upward electron beams were measured by the Juno JADE instrument in the northern hemisphere, low‐latitude auroral zone source region. In this study we report on how these electron beams interact with plasma near and within the Jovian hectometric (HOM) emission (1 MHz 5 MHz) source region. Within the source region large upward loss cones are observed in the northern polar region at radial distances of 2Rj, magnetic latitude of . Intense, narrow electron beams ( 3 keV) are then observed, but within one second wave‐particle scattering is observed, filling the loss cone to energies 50 keV. These energies persist for several seconds before fading, leaving an empty loss cone again. The loss cone provides a free‐energy source for HOM emission resulting from the cyclotron maser instability. We use quasilinear analysis to examine the generation of HOM and the dynamics of wave‐particle interaction of the electron beams with HOM, and the generation via Landau interaction of whistler mode emission. The dynamic spectrum of the HOM emission generated by the loss‐cone electrons as well as that of the low‐frequency whistler‐mode waves generated by the up‐going electron beam can be constructed by quasilinear theory, which compare well with observation. The saturated state of the energetic electron velocity distribution function constructed via quasilinear theory also compare reasonably with observation.

Abstract As Global Navigation Satellite System electromagnetic waves pass through the ionosphere, especially in auroral zones, ionospheric irregularities cause the waves to scintillate. Identification of the ionosphere scattering layer is an important factor in understanding the cause of scintillation. This work implements two techniques to determine whether signal scattering for Global Positioning System L1 and L2C signals might be in the E‐ or F‐layer. The first technique used is an updated process of Sreenivash et al. (2020, https://doi.org/10.1029/2018RS006779), in which the Poker Flat Incoherent Scatter Radar (PFISR) maximum electron densities and their uncertainties hypothesize the layer in which scattering has occurred. The density‐based method predicts a majority of F‐region scintillation events for 2014, with a majority of E‐region events found for 2015 to 2019. The second technique consists of using the ratio of the 630 (red) to the 428 nm (blue) intensity in optical all‐sky images (ASIs) to hypothesize the scattering layer with ASI. The decision threshold is set to 1.35 based on the GLobal airglOW model. From 2014 to 2018 174 events have both PFISR data and ASIs with clear viewing conditions and alignment to within 25° of magnetic zenith. There is an agreement between the two methods for 128 (74%) events.