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Available literature indicates that various studies do not adequately provide information on the temporal locations of solar wind structures, which leaves a gap that needs to be filled. In response, a study of the geomagnetic storm of Oct 13, 2016, is carried out to fill this gap by identifying the spatiotemporal locations of solar wind structures responsible for the geomagnetic storm to effectively elucidate ionospheric responses during a geomagnetic storm, as well as enable the determination by further studies of the global relative geo-effectiveness of these structures as it were. Primarily, the investigation aimed to confirm if the typical simplified structure of all CMEs consists of a forward shock followed by the sheath and the magnetic cloud. Now, this study has brought forth some distinct/previously unseen results: A typical simplified structure of a CME consists of a forward shock followed by the sheath and the magnetic cloud. Our findings revealed a sandwich structure of sheath-magnetic cloud-sheath following the forward shock with the following spatiotemporal arrangement for the solar wind structures: (a) Sheath I, observed from 2 Oct 13 to 3 Oct 14, spanning: (i) the initial phase: 2–7 UT, Oct 13 (ii) the main phase:7–23 UT, Oct 13 (iii) the early parts of the recovery phase: 0–3 UT, Oct 14 (b) The Magnetic Cloud, observed through 03–09 UT, Oct 14, during the recovery phase. (c) Sheath II, observed during the recovery phase from 9 to 23 Oct 14. [ABSTRACT FROM AUTHOR]

Recent studies based upon both observations and numerical simulations have indicated the impacts of the intense geomagnetic storms induced by Coronal Mass Ejections (CMEs) on the neutral dynamics in the mesosphere and lower thermosphere (MLT). Even in the midlatitude MLT, far equatorward of subauroral zone, significant variations were reported. Aurora is one of the major dynamic drivers in the MLT in high latitudes, but observations of the neutral dynamic variations under the aurora in the storm time MLT are sparse. The lack of such MLT observations during the presence of aurora leads to a critical gap in the understanding of upper atmospheric dynamics. In this paper, we present the unprecedented observations under the aurora during the Gannon Geomagnetic Storm in May 2024 by the Na Doppler lidar at Utah State University (42°N, 112°W) and the Advanced Mesospheric Temperature mapper (AMTM) at the nearby Bear Lake observatory (BLO). Significant warming (as much as ∼50 K) accompanied by fast equatorward flow in the lower thermosphere (up to ∼100 m/s changes in the meridional wind above 100 km altitude) were observed. The temperature enhancement (∼10 K) of the hydroxyl layer during the same period is also captured by the AMTM. Intriguingly, significant storm time depletion of sodium (Na) abundance on the topside of the mesospheric Na layer above 105 km, as much as more than 80%, was also observed. These observations provide insight for future investigations on the MLT responses to the intense geomagnetic storms, especially the role of aurora in these events. [ABSTRACT FROM AUTHOR]

In this short communication, we qualitatively analyze possible effects of the 10 October 2024 geomagnetic storm on accelerating the reentry of a Starlink satellite from very low-Earth orbit (VLEO). The storm took place near the maximum of solar cycle (SC) 25, which has shown to be more intense than SC24. Based on preliminary geomagnetic indices, the 10 October 2024, along with the 10 May 2024, were the most intense events since the well-known Halloween storms of October/November 2003. By looking at a preliminary version of the Dst index and altitudes along with velocities extracted from two-line element (TLE) data of the Starlink-1089 (SL-1089) satellite, we observe a possible connection between storm main phase onset and a sharp decay of SL-1089. The satellite was predicted to reenter on 22 October, but it reentered on 12 October, 10 days before schedule. The sharp altitude decay of SL-1089 revealed by TLE data coincides with the storm main phase onset. We compare the deorbiting altitudes of another three satellites during different geomagnetic conditions and observe that the day difference between actual and predicted reentries increases for periods with higher geomagnetic activity. Therefore, we call for future research to establish the eventual causal relationship between storm occurrence and satellite orbital decay. As predicted by previous works, SC25 is already producing extreme geomagnetic storms with unprecedented satellite orbital drag effects and consequences for current megaconstellations in VLEO. [ABSTRACT FROM AUTHOR]

Hot flow anomalies (HFAs) and foreshock bubbles (FBs) are two types of transient phenomena characterized by flow deflected and hot cores bounded by one or two compressional boundaries in the foreshock. Using conjunction observations by the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, we present an MHD HFA with a core filled with magnetosheath material around the bow shock and a typical kinetic FB associated with foreshock ions upstream of the bow shock, occurring simultaneously under the same solar wind/interplanetary magnetic field (IMF) conditions. The displacements of the bow shock moving back and forth along the sun-earth line are observed. Electron energy shows enhancements from ∼50 keV in the FB to ∼100 keV in the HFA core, suggesting additional acceleration process across the bow shock within the transient structure. The magnetosheath response of an HFA core-like structure with particle heating and electron acceleration is observed by the Magnetospheric Multiscale (MMS) mission. Ultralow frequency waves in the magnetosphere modulating cold ion energy are identified by THEMIS, driven by these transient structures. Our study improves our understanding of foreshock transients and suggests that single spacecraft observations are insufficient to reveal the whole picture of foreshock transients, leading to an underestimation of their impacts (e.g., particle acceleration energy and spatial scale of disturbances). [ABSTRACT FROM AUTHOR]

Underground space in Xuzhou City, North China, has become a favorable site for continuous geomagnetic observation to reveal geomagnetic-field variations and to monitor seismic activity due to its distinct advantage of an "ultra-quiet" and "ultra-clean" environment with low electromagnetic interference. In order to evaluate the underground electromagnetic environment at the Longdong coal mine area (LCMA) in Xuzhou City and establish an underground geomagnetic observatory, we conducted a pilot experiment of continuous geomagnetic observations synchronously underground and on the ground during May 2023. In this experiment, two close-space fluxgate magnetometers were deployed in the underground roadway of the LCMA to observe the variations of geomagnetic three components simultaneously, and a proton magnetometer was installed on its ground to observe the variation of geomagnetic total field. Furthermore, we analyzed the features of the wavelet spectrum of these observed data, variation curves of the geomagnetic field, and coupling of the geomagnetic-field variations between underground and ground. In addition, we investigated the characteristics of different frequency bands and horizontal gradient of the underground geomagnetic variation. Our achievements are as follows: 1) the underground geomagnetic environment has the advantage of being stable and clean with a low level of background noise and thus is suitable for high-precision, long-term, and continuous observation of the geomagnetic field; 2) the variation of the geomagnetic field underground is well coupled with that on the ground, with minor differences primarily attributed to an induced magnetic field generated in the surrounding rocks by the external magnetic-field variation; 3) underground geomagnetic observation can clearly record rich time-varying information of the geomagnetic field including calm variation, magnetic storms, geomagnetic pulsations and so on. Moreover, the geomagnetic gradient field contains higher-resolution time-varying information than the conventional geomagnetic field. Our pilot experiment suggests favorable underground sites with low background noise at the LCMA and provides valuable references for understanding the spatiotemporal variation characteristics of geomagnetic field. Based on the findings of our pilot experiment, an underground geomagnetic observatory and calibration station will be established at the LCMA, enabling high-precision, continuous geomagnetic and electromagnetic observation experiments in the future. These efforts will provide crucial constraints for the study of the variation of the geomagnetic-field variation, as well as seismic activity monitoring and disaster early warning related to the Tan-Lu fault zone. [ABSTRACT FROM AUTHOR]

The study of the Earth's ionosphere is a topic that has increased in relevance over the past few decades. The ability to predict the ionosphere's behavior, as well as to mitigate the effects of its rapid changes, is a matter of primary importance in satellite communications, positioning, and navigation applications at present. Ionosphere perturbations can be produced by geomagnetic storms correlated with the solar activity or by earthquakes, volcanic activities, and so on. The monitoring of space weather is achieved through analyzing the Vertical Total Electron Content (VTEC) and its anomalies by means of time series, maps, and other derived parameters. In this study, we outline a strategy to estimate the VTEC in real-time, its rate of change, and the corresponding Signal-to-Noise Ratio (SNR) based on dual-frequency GNSS Doppler observations. We describe how to compute these parameters from GNSS data for a regional network using Adjusted Spherical Harmonic Analysis (ASHA) applied to a local model. The proposed method was tested to study ionospheric anomalies for two seismic events: the 2015 Nepal and 2023 Turkey earthquakes. In both cases, anomalies were detected in the maps of the differential VTEC (DTEC), differential VTEC rate, and SNR of the VTEC produced close to the earthquake zone. The robustness of the results is strongly related to the availability of a dense Ionosphere Pierce Point (IPP) cloud on the ionospheric layer and surrounding the studied area. At present, the distribution of Continuously Operating Reference Stations (CORSs) around the world is insufficiently dense and homogeneous in certain regions (e.g., the oceans). Robustness can be improved by increasing the number of CORSs and developing new models involving measurements over ocean surfaces. [ABSTRACT FROM AUTHOR]

• No positive storm effect observed in the Pacific mid-latitude regions during March 2023 storm. • Hemispheric asymmetry is observed in the super-fountain effect during March-23 storm. • Disturbed thermospheric winds display a non-uniform planetary distribution, particularly evident during the March-23 storm. This study explores the ionospheric disturbances induced by the March 2023 geomagnetic storm, offering insights into the complex interplay between space weather events and the Earth's upper atmosphere. In this regard, data from ionospheric maps (global and regional electron contents) and topside plasma density (provided by the Swarm satellites) have been used. Furthermore, the findings are compared with those of the March 2015 St. Patrick's Day storm of solar cycle 24, which exhibited notably similar onset conditions. The Global Electron Content (GEC) displays substantial positive surges in the African, Pacific, and American sectors, with a notable enhancement in the American sector on March 24, 2023. During the recovery phase (March-23 storm), negative storm effects are observed across all longitudinal sectors, with greater intensity at low-latitudes compared to mid-latitudes. Moreover, the study highlights discrepancies in positive storm effects when compared to the St. Patrick's Day storm. During the March-2023, there was no positive storm effect observed in the pacific mid-latitude regions. This longitudinal difference in occurrence of positive storm may be attributed to potential influences from variations in the z-component of the interplanetary magnetic field and energy inputs into the magnetosphere. A super fountain effect is observed exclusively in the American sectors during both storms, exhibiting a noticeable hemispheric asymmetry. The non-uniform planetary distribution of disturbed thermospheric winds likely played a major role in the ionospheric asymmetry in the American region during the 2023 event. [ABSTRACT FROM AUTHOR]

On February 8, 2022, approximately 40 of the 49 Starlink satellites were reported to have lost altitude, leading to atmospheric re-entry. SpaceX reported that the orbital decay on Starlink satellites was considered to be linked to a geomagnetic storm that was initiated on February 3, 2022. We attempted to analyze the cause of orbital decay by sampling all Starlink satellites registered in the SpaceTrack database and then tracing some space weather parameters and species density variations in the thermospheric layer. We employed the solar wind and IMF Bz to see their impact on geomagnetic activity. Moreover, we also analyzed the electric field Ey, Dst, AE, and Ap indices in addition to the solar EUV flux to see their impact on the Starlink satellite environment. We discovered three geomagnetic substorms during the analysis period: two successive substorms on February 4 and 5, and one additional substorm on February 10. We inferred that magnetic substroms significantly affected species densities, mainly O, O2, and N2, around some Starlink satellites, leading to an increase in atmospheric drag. There was a time delay between the substorms and orbital decay on Starlink satellites. However, some Starlink satellites were not affected by geomagnetic substorms due to insignificant changes in their environment. The reason for this is that, despite having lower altitudes, all decaying Starlinks were located in the midnight-dawn sector, in which the drift of ionospheric currents was predominantly driven by westward electrojets. On the other hand, all non-decaying Starlink satellites that had higher altitudes resided in the dusk–midnight sector of magnetic local time, where the impact of substorms insignificantly affected their altitudes. [ABSTRACT FROM AUTHOR]

Ionospheric electron density (IED) and vertical total electron content (VTEC) are two of the most important characteristics that interpret the ionosphere. Today, satellite geodesy plays an important role in providing these data. Apart from monitoring the ionosphere by means of Global Navigation Satellite System observations, predictions of these ionospheric characteristics have also been taken into consideration. The majority of prediction methods in the ionosphere are focused on VTEC prediction. The continuity equation in the ionosphere is a spatiotemporal partial differential equation that can be used to predict both IED and VTEC. In this study, we address this issue during May 8, 2016, which was a day of high geomagnetic activity. For this purpose, first, high-accuracy IED grids with a spatial resolution of 0.5° × 0.5° in longitude and latitude, 50 km in altitude, and a temporal resolution of 10 min are prepared. These IED grids are called analysis grids and are derived by assimilation of GPS-derived VTECs into the background IED grids provided by international reference ionosphere. Second, the analysis grids can be utilized as the initial and boundary values in the continuity equation to predict IED for the next 3 h with a step of 10 min. The analysis grids are constructed over the Iran region, and the performance of the continuity equation in the ionosphere prediction is investigated during the strongest geomagnetic storm of 2016. Finally, the accuracy of the predictions has been evaluated in two ways. First, analysis grids with high accuracy are available for each epoch in which the prediction is presented. On average, the root mean square (RMS) of the differences between the predicted IEDs and the analysis IEDs is 1.66 × 1010 el/m3 for 1-h predictions and 5.33 × 1010 el/m3 for 3-h predictions. Second, by numerical integration of the predicted grids in the vertical direction, VTECs are estimated and compared with VTEC values of test data that were already known. On average, the RMS of their difference was 1.29 total electron content unit (TECU) for 1-h predictions and 2.57 TECU for 3-h predictions. An acceptable accuracy for both IED and VTEC prediction by a continuity equation has been obtained up to 3 h on the most active ionospheric day. [ABSTRACT FROM AUTHOR]

Thermospheric mass densities are investigated to explore their responses to solar irradiance and geomagnetic activity during the period from 31 October to 7 November 2021. Utilizing data from the Global Navigation Satellite System (GNSS) payload and an ionization gauge mounted on the Orbital Neutral Atmospheric Detector (OAD) payload onboard the QQ-Satellite, thermospheric mass densities are derived through two independent means: precise orbit determination (POD) and pressure measurements. For the first time, observations of these two techniques are compared and analyzed in this study to demonstrate similarities and differences. Both techniques exhibit similar spatial–temporal variations, with clear dependences on local solar time (LT). However, the hemispheric asymmetry is almost absent in simulations from the NRLMSISE-00 and DTM94 models compared with observations. At high latitudes, density enhancements of observations and simulations are shown, characterized by periodic bulge structures. In contrast, only the OAD-derived densities exhibit wave-like disturbances that propagate from two poles to lower latitudes during geomagnetic storm periods, suggesting a connection to traveling atmospheric disturbances (TADs). Over the long term, thermospheric mass densities derived from the two means of POD and the OAD show good agreements, yet prominent discrepancies emerge during specific periods and under different space-weather conditions. We propose possible interpretations as well as suggestions for utilizing these two means. Significantly, neutral winds should be considered in both methods, particularly at high latitudes and under storm conditions. [ABSTRACT FROM AUTHOR]

The global navigation satellite system (GNSS) ionospheric tomography technique can reconstruct the 3D images of ionospheric electron density (IED) in response to geomagnetic storms. In a common practice, the absolute IED values are first reconstructed with tomography and then the IED disturbances are calculated for the study of geomagnetic storm. However, the ionosphere disturbances derived from the conventional method are often contaminated by the initial value error and the slant total electron content (STEC) uncertainty. Therefore, this paper proposes an improved ionospheric tomography method for a direct inversion of global IED disturbance. In this improved method, IED disturbances are tomographically reconstructed from the zero initial value with detected STEC residuals. The global ionosphere maps (GIMs) released by the Center for Orbit Determination in Europe (CODE) are used to generate virtual STEC residuals for compensating the uneven and sparse distribution of the global GNSS network. The success rates for disturbance detection of the improved method under different simulation conditions are in the range of 80–90 %. The ionosphere shows a strong reaction to geomagnetic storms with significant IED disturbances in the altitude of 100–600 km. Based on the tomographic IED disturbance values, this paper fully analyzes the evolution of global IED disturbances during the geomagnetic storm on 25–26 August 2018. The ionospheric disturbances are slightly delayed compared with the occurrence of the geomagnetic storm. IED disturbances first appeared in the polar and low latitude regions at the altitude of 200–400 km and gradually expanded worldwide. As the geomagnetic storm reached the peak, the ionospheric disturbances were at their strongest with duration of 3–5 h. In general, the improved tomography method can retrieve the accurate global IED disturbances and clearly show positive and negative disturbances caused by the geomagnetic storm. [ABSTRACT FROM AUTHOR]

On March 23 and 24, 2024, the M-class and X-class solar storms significantly intensified. Subsequently, from March 24 to 26, the monitoring station's Kp index notably increased, at times exceeding 8, indicating that a severe geomagnetic storm was occurring. During this period, the IGS Global Ionosphere Maps (GIMs) displayed a substantial decrease in Total Electron Content (TEC) in Western Europe due to the impact of the intense geomagnetic storms. To investigate this occurrence, data from the Lowell GIRO Data Center were utilized. The analysis revealed that a concentrated solar flare eruption on March 23, 2024, triggered geomagnetic storm events on Earth, causing significant ionospheric anomalies in Western European countries. Specifically, compared to typical levels, parameters such as foF2, m3000F2, and TEC values experienced significant reductions in Western European countries. Moreover, the hmF2 data exhibited higher values at night and lower values during the day, deviating from the expected diurnal pattern. Analysis of the Rate of TEC Index (ROTI) indicated varying effects of geomagnetic storms across different latitudes in Western Europe. Through detailed graphical analysis, this study elucidates the alterations in the ionosphere under geomagnetic storm conditions in Western Europe, shedding light on the dynamic behavior of the ionosphere during a specific timeframe. [ABSTRACT FROM AUTHOR]

In 2023 April, a low-latitude aurora observed by the all-sky camera at Hanle, Ladakh, India (33°14'N geographic latitude), generated significant interest. This was the first such aurora recorded from the Indian region in the space era and occurred during a moderate solar storm. This study explores this low-latitude auroral sighting, which happened during the sheath-region passage of an interplanetary coronal mass ejection. We analyze in situ multispacecraft particle measurements and geomagnetic field observations from both ground-based and satellite-based magnetometers. The auroral observations at Hanle coincided with intense substorm activity. Our findings indicate that the aurora did not actually reach India; the equatorward boundary was beyond 50°N geographic latitude. Enhanced electron fluxes with energies below 100 eV were detected at 54°N geographic latitude at about 830 km altitude in the predawn sector (4–5 hr local time). In the midnight sector, the equatorward boundary is estimated to be around 52°N geographic latitude, based on Hanle observations and considering emission altitudes of 600–650 km due to low-energy electrons. Thus, the low-latitude red aurora observed from India resulted from the emissions at higher altitudes due to low-energy electron precipitation in the auroral oval and a slight equatorward expansion of the auroral oval. The low-energy electrons likely originated from the plasma sheet and were precipitated due to enhanced wave–particle interactions from strong magnetosphere compression during high solar wind pressure. This study is crucial in understanding low-latitude auroras in the modern space era. [ABSTRACT FROM AUTHOR]

In this study, we investigated terrestrial-origin O+ ions below 1 keV around the Moon using data from the Kaguya satellite between December 2007 and June 2009. These terrestrial-origin low-energy O+ ions were identified based on three parameters: the periodicity of O+ ion count enhancement corresponding to Kaguya's 2-h orbital period, the count ratio of O+ ions to Na+ and Al+ ions, and the direction of ion bulk velocity in the Sun–Earth direction. We identified three intervals that included such O+ ions: 14:30–20:30 UT on June 19, 2008, 19:00 UT on July 16, 2008 to 03:00 UT on July 17, 2008, and 14:00–24:00 UT on June 7, 2009. These intervals were found in the dawn sector, the dusk sector, and the midnight to dawn sector within the magnetotail, respectively. We examined the relation between geomagnetic storm conditions and increases in terrestrial-origin O+ ion counts and found that all three intervals occurred during the late recovery phase of moderate/weak magnetic storms. Since moderately/weakly disturbed conditions (Dst = –40 nT to –20 nT) account for approximately 21% of the total time between 1957 and 2016, we suggest that low-energy O+ ions from the Earth have a non-negligible impact on the ion composition and the ion mass density in the lunar plasma environment. [ABSTRACT FROM AUTHOR]

Understanding the effects of east‐west component of interplanetary magnetic field (IMF‐By) on the equatorial ionospheric electrodynamics is challenging due to the complex response caused by the simultaneous occurrence of multiple mechanisms during disturbed times. The extreme geomagnetic storm on 10 May 2024 caused by multiple‐ICME interactions accompanied with unprecedented IMF‐By magnitudes and its polarity, changed from west to east by 130 nT during northward IMF‐Bz turning. The ground ionosonde observations of h'F from near‐equatorial locations, along with the latitudinal profiles of plasma densities from Swarm satellites reveal the first observational evidence of the impact of strong IMF‐By near the dusk‐terminator (17–19.5 LT), causing strong dawn‐to‐dusk ionospheric electric fields during northward IMF‐Bz. This electric field produces large uplift of the ionospheric plasma near equator and subsequent super‐fountain effect near the dusk. The combined effect of increased IMF‐By amplitudes and viscous terms might have resulted into the enhanced coupling of solar wind with the magnetosphere. Plain Language Summary: The southward component of interplanetary magnetic field (IMF‐Bz) is a primary driver for the solar wind‐magnetosphere coupling, which produces geomagnetic disturbances on the Earth. Whereas east‐west component of IMF (IMF‐By) can modify the effects of these disturbances. Understanding the effects of IMF‐By on the equatorial ionosphere is challenging due to the complex response caused by the simultaneous occurrence of multiple mechanisms during disturbed times, such as ring current, prompt penetration and disturbance dynamo electric fields etc. During the extreme geomagnetic storm which occurred on 10 May 2024, the IMF‐By component was very intense. Both, Bz and By components of IMF made sudden and giant transitions, changing their orientation rapidly. We have investigated the effects of this rarest event on the equatorial ionospheric electric fields. We find penetration of strong eastward electric field near dusk during northward and eastward IMF conditions. Key Points: Unprecedented IMF‐By amplitudes during northward IMF show strong eastward ionospheric electric fields at dusk near equatorThe effects are strongest near dusk and overshielding effects are evident near noonFirst observational evidence of the impact of strong IMF‐By on the equatorial ionosphere near dusk [ABSTRACT FROM AUTHOR]

We calculated variations in the cosmic ray geomagnetic cutoff rigidity ΔRef during a complex two-stage magnetic storm on November 9–10, 2004, using calculations of particle trajectories in the model magnetic field of the magnetosphere. The response of ΔRef to changes in solar wind and magnetosphere parameters reflects the nonsmooth two-stage evolution of this storm. It is found that the curve of changing values that ΔRef take as a function of the studied parameters during the main phases of each stage of the storm does not coincide with the curve during the recovery phases, which is a sign of hysteresis. As a result, two hysteresis loops are formed, one for each stage of the storm of November 9–10, 2004. The ambiguous dependence of ΔRef values on the studied parameters, which change cyclically during the development of magnetospheric current systems and their subsequent relaxation, is responsible for the formation of the loops. The configuration of two loops similar to those characteristic of dielectric hysteresis seems to be related to the abrupt change from Bz > 0 to Bz < 0, which delimits the stages of the studied storm. [ABSTRACT FROM AUTHOR]

Solar wind parameters (SWP) and geomagnetic indices act as defining factors between the Earth's magnetosphere-ionosphere and the Sun. Models between SWP and indices should be examined seriously to better interpret the dynamics of geomagnetic storms (GSs). This work touches on the first two weak (25 January and 22 February) and moderate (14 January and 13 March) GSs of the 2022 year with an artificial neural network (ANN) model. The models are based on SWP (E, v, P, T, N, Bz) and geomagnetic indices (Dst, Kp, ap). The ANN employs SWP as inputs and indices as outputs, predicting the indices via SWP. The Scaled Conjugate Gradient (trainscg) algorithm is used for the back-propagation iteration. Four different geomagnetic storms, which are weak; Dst = -35 nT (25 January), Dst = –32 nT (22 February), and moderate storms; Dst = -91 (14 January) nT, Dst = -85 nT (13 March), are considered as case studies. The results of the estimations have acceptable accuracy. While the model is trained with mean square error (MSE) loss function, the accuracy of the model is evaluated by both mean square error (MSE) and mean error (ME). [ABSTRACT FROM AUTHOR]

Magnetic reconnection in the near-Earth magnetotail is responsible for explosive release of energy during substorms and auroral breakups. This near-tail reconnection was previously assumed to occur around the midnight meridian, where earthward flows were typically observed. Based on observations of tailward-moving plasmoids, the Geotail spacecraft mission discovered that the reconnection location was displaced toward dusk. This dusk preference is presumably caused by the Hall electric field, as was suggested later in simulations. However, recent spacecraft observations have indicated that the reconnection was displaced toward dawn, and not dusk, in Mercury's magnetotail. In response to this controversy, our study aims to clarify the dawn–dusk location of fast plasma flows in the near-Earth magnetotail. Through a comprehensive reinterpretation and integration of previous statistical results, we found that the dusk preference is generally evident for tailward flows but is often absent for earthward flows. These results indicate that the statistical results of earthward flows are sensitive to event selection criteria. We conclude that the dawn–dusk location of earthward flow is statistically unclear at the time of substorm onset. Similarly, in the magnetotail of other planets, the dawn–dusk location of planetward flow may be sensitive to event selection criteria. Hence, reconnection may occur predominantly on the duskside in Mercury's magnetotail. This hypothesis will be tested using observations of tailward-moving plasmoids by the BepiColombo Mio spacecraft, which will begin orbital observations of Mercury in the year 2026. [ABSTRACT FROM AUTHOR]

On May 11, 2024, an extreme G5-class geomagnetic storm triggered a spectacular and unusual display of colorful auroras in mid- to low-latitude regions all over the world. In Japan, auroras were seen not only from Hokkaido, the northernmost island, but also from the northern and central parts of Honshu, the main island. The widespread availability of commercial digital cameras among the public led to a flooding of high-resolution auroral images on social media. This study reports on the appearance of a blue-dominant aurora during a storm-time substorm on this day and its magnetic field-aligned and longitudinal structures captured by citizen scientists. Observations from two photographers at different locations revealed that the aurora was located at approximately 40 degrees magnetic latitude and magnetic local time (MLT) of 23 h, spanned about 1200 km (1-h MLT) in the longitudinal direction with three separated structures, and ranged in altitude from 400 km to at least 900 km. Simultaneous photometric measurements suggested that this blue-dominant aurora likely included emissions at 427.8 nm. While previous studies have noted the existence of emissions at 427.8 nm in low-latitude auroras, this is the first time that a blue-dominant low-latitude aurora has been spatially identified and shown to have longitudinal and field-aligned structures. Additionally, previous studies suggested that blue emissions in low-latitude auroras are produced by energetic neutral atoms from the ring current. However, identifying longitudinal and field-aligned structures in this study may need an alternative explanation. [ABSTRACT FROM AUTHOR]

This study provides a comprehensive investigation into ionospheric perturbations associated with the Mw 7.5 earthquake on the Noto Peninsula in January 2024, utilizing data from the International GNSS Service (IGS) network. Focusing on Total Electron Content (TEC), the analysis incorporates spatial mapping and temporal pattern assessments over a 30-day period before the earthquake. The time series for TEC at the closest station to the epicenter, USUD, reveals a localized decline, with a significant negative anomaly exceeding 5 TECU observed 22 and 23 days before the earthquake, highlighting the potential of TEC variations as seismic precursors. Similar patterns were observed at a nearby station, MIZU, strengthening the case for a seismogenic origin. Positive anomalies were linked to intense space weather episodes, while the most notable negative anomalies occurred under geomagnetically calm conditions, further supporting their seismic association. Using Kriging interpolation, the anomaly zone was shown to closely align with the earthquake's epicenter. To assess the consistency of TEC anomalies in different seismic events, the study also examines the Mw 7.1 Nichinan earthquake in August 2024. The results reveal a prominent negative anomaly, reinforcing the reliability of TEC depletions in seismic precursor detection. Additionally, spatial correlation analysis of Pearson correlation across both events demonstrates that TEC coherence diminishes with increasing distance, with pronounced correlation decay beyond 1000–1600 km. This spatial decay, consistent with Dobrovolsky's earthquake preparation area, strengthens the association between TEC anomalies and seismic activity. This research highlights the complex relationship between ionospheric anomalies and seismic events, underscoring the value of TEC analysis as tool for earthquake precursor detection. The findings significantly enhance our understanding of ionospheric dynamics related to seismic events, advocating for a comprehensive, multi-station approach in future earthquake prediction efforts. [ABSTRACT FROM AUTHOR]

Magnetic storm, ionospheric storm, atmospheric storm, and electrical storm are the components of a geospace storm resulting from a solar storm. In the literature, the main attention is paid to the analysis of severe and extreme geospace storms. It is these storms that have the greatest impact on the Earth–atmosphere–ionosphere–magnetosphere system. They are most dangerous for space-based and ground-based technological systems. Such storms have a significant impact on human well-being and health. Minor and moderate storms are much less studied than severe and extreme ones. There are good reasons to believe that such storms can have some impact on the systems and people. It is important that the frequency of occurrence of moderate storms is much greater than the frequency of occurrence of severe storms. All this determined the relevance of this work, which consists in the study of magnetic disturbances that arise during moderate geospace storms, which receive undeservedly little attention. The purpose of this paper is to analyze on a global scale the temporal variations of geomagnetic field components during moderate magnetic storms on April 28–29 and May 1–2, 2023. The latitudinal dependence of the geomagnetic field components temporal variations during two moderate magnetic storms in April–May 2023 and on reference days was analyzed on a global scale using the data of the global network of Intermagnet stations. The limits of fluctuations in the level of the geomagnetic field under quiet conditions and during moderate storms were estimated. The range of variations in the geomagnetic field level under quiet conditions decreased from 200–260 to 30–50 nT with decreasing geographic latitude. During the storms, these limits increased 1.3–2.1 times. The variations in the level of components at stations equidistant from the equator were close. This is true for both the Western and Eastern Hemispheres. The fluctuations of the geomagnetic field level at the stations operating approximately at the same latitude but in different hemispheres were also close. [ABSTRACT FROM AUTHOR]

Using the quartile-based statistical' as this approach is used in the present study approach G-PS-VTEC data of the Lhasa observing station (Geographical Lat. 29.66° N, Geographical Long. 91.10° E) are analysed for six months from July 1, 2019, to December 31, 2019, in the light of eleven major shallow earthquakes (M ≥ 5.0, depth < 30 km) occurred in India, Nepal, and China within a radius of 1500 km assuming it as a center. The results of the analysis show anomalous TEC enhancements of 0.08–15.26 TECU, 1–28 days before the occurrence of these earthquakes. The percentage of TEC enhancements seen before these earthquakes range from 0.74–113.20%. Co-seismic TEC enhancements are also noted for the earthquakes (M = 5, 5.4, 5, 5.3, 5) of August 11, 31, 2019, September 7, 2019, October 27, 2019, and December 9, 2019. The range of co-seismic TEC enhancements is 0.01–4.25 TECU and percentage range of these enhancements is 0.07–31.08%. The post TEC enhancements are observed for the seismic events. The range of post TEC enhancements and percentage enhancements in it are 0.12–6.54 TECU and 1.52–36.41% respectively and the duration of these enhancements is found to vary from 1–21 days. Further, these enhancements in TEC data are also examined in the light of magnetic storms and solar activity and it is found that none of these enhancements are associated with solar activity and magnetic storms. The anomalous days are also confirmed by one more statistical technique. Finally, the possible generation and propagation mechanisms for the observed anomalies are also discussed. [ABSTRACT FROM AUTHOR]

Geomagnetic storms are disorders in Earth's magnetic field triggered by solar activity. This research attempts to foretell the total electron content (TEC) using the Kriging and AI model in both low and mid-latitude stations during strong geomagnetic storms that happened on March 17, 2015 and February 3, 2022. This research paper focuses on predicting and analysing TEC anomalies in the ionosphere during the solar storm by using three models: ordinary kriging (OK), cokriging (CoK) and recurrent neural network (RNN). The predicted TEC values by the models are justified with the TIEGCM and KMPCA models. Parameters like RMSE, CC, MAE, and MAPE were applied to assess the execution of predictive models and to quantify the accuracy of predictions. The average RMSE for TEC predicted in the low-latitude region ranges from 4.90 to 5.41, 5.85 to 6.26 and 8.50 to 9.90 for the OK, CoK, and RNN models, respectively. Likewise, the average RMSE for TEC predicted in the mid-latitude region ranges from 1.81 to 4.04, 1.91 to 4.24 and 2.77 to 5.38 for the OK, CoK, and RNN models, respectively. The performance evaluation parameters show that the OK performs better than the CoK and RNN models. [ABSTRACT FROM AUTHOR]

Here we studied the planetary features of the spatiotemporal distribution of ionospheric electrojets recorded in the onset of a substorm and in time on the activity maximum of three very intense substorms (with an AL-index from –1200 to –1700 nT) observed during the main phase of the strong magnetic storm on March 23−24, 2023. We have analyzed the substorms by applying the global maps of the planetary distribution of high-latitude ionospheric currents, compiled from simultaneous magnetic measurements on 66 low-orbit satellites of the AMPERE project, as well as ground-based magnetograms from the Scandinavian IMAGE profile and mid-latitude IZMIRAN stations located in the same longitudinal region. It was established that the onset of all the studied substorms on the IMAGE meridian was accompanied by the development of a nighttime current vortex with clockwise rotation, which is an indicator of an increase in downward field-aligned currents. The ground-based mid-latitude observations at the IZMIRAN station network confirmed that the center of the current wedge of the substorm was located in the nighttime sector significantly east of the IMAGE meridian. In the time of the substorm intensity maximum, a similar but more extensive current vortex was observed in the morning sector, which is probably typical of intense substorms. [ABSTRACT FROM AUTHOR]

Ionospheric disturbances that accompanied the moderate magnetic storm on January 14–20, 2022, are analyzed. The work is based on data obtained from vertical and oblique ionospheric sounding in the northeastern region of Russia and supplemented by observations at HF radars and magnetic observatories. It has been revealed that the amplitudes of positive and negative ionospheric disturbances accompanying this storm are comparable to those observed on other days of January during weak magnetic storms and disturbances. The specific features of the disturbances observed only during the storm in question are as follows: (1) a midnight–morning increase in the maximum observed frequency of one-hop mode of HF radio wave propagation on the paths Norilsk–Tory and Magadan–Tory on 14 January; (2) enhancement of nighttime fluctuations of the critical frequency in the F2 layer in Irkutsk and the maximum observed frequency of one-hop mode on the path Magadan–Tory on January 15; and (3) morning–midday Es layers with limiting frequencies reaching 7 MHz that were observed in mid-latitudes at the end of the first day and beginning of the second day of the storm recovery phase. [ABSTRACT FROM AUTHOR]

During the expansion phase of a substorm, the poleward jump of auroras (breakup) and the expansion of the auroral bulge are observed. The expansion is accompanied by a negative magnetic bay under the aurora and a positive magnetic bay at mid-latitudes. The magnitude of the negative bay is characterized by the auroral AL-index. The Mid-Latitude Positive Bay index (MPB-index) was previously proposed in order to characterize the positive bay. In this article, the statistical relationship of the MPB-index with the geomagnetic activity at different latitudes and with the parameters of the solar wind and interplanetary magnetic field is investigated. It is shown that all extremely high values of the MPB-index (above 10 000 nT2) are observed during strong geomagnetic storms (when the Dst-index falls below –100 nT), all extremely strong geomagnetic storms (when the Dst-index falls below –250 nT) are accompanied by extremely high values of the MPB-index. Statistically, the MPB-index increases with increasing geomagnetic activity at any latitude. On average, the MPB-index increases with increasing interplanetary magnetic field magnitudes and any of its components. However, for the Bz-component, large values of the MPB-index are observed at its southward orientation. For the plasma parameters of the solar wind, the MPB-index increases most strongly with the increase of its speed. The dependence on the dynamic pressure and on the value of the EY-component of the electric field of the solar wind is also strong. However, the MPB-index weakly depends on the density and temperature of the solar wind. [ABSTRACT FROM AUTHOR]

Large geomagnetic disturbances are fairly rare events, even near the top of the solar cycle. These are mostly caused by particle radiation from the Sun. The flow of these particles is called solar wind. The terrestrial magnetosphere and ionosphere create magneto-hydro-dynamic waves that produce an increase in the magnetic field on the Earth's surface. The recording of the geomagnetic field is carried out in geomagnetic observatories and with the help of satellites. Magnetic observatories are permanent measuring stations that monitor geomagnetic field variations with very high precision both in time and in amplitude. Several calculation methods were used to quantify these variations, resulting in various indices of magnetic activity. They are calculated either at the planetary level or for specific areas on Earth (equatorial indices (Ae), daily indices (Ap), planetary indices (Kp), geomagnetic activity index (Dst)). In the present work, the geomagnetic storm produced on March 24, 2024 was analysed. There are situations where the different way of reporting the geomagnetic indices (Dst and Kp) can lead to the classification of the same phenomenon in two different categories (average storm after Dst and strong storm after Kp). [ABSTRACT FROM AUTHOR]

The 25th Solar Cycle began in December 2019 and is heading towards its maximum. Every 11 years or so, the Sun goes through periods of low (minimum) or high (maximum) solar activity, which is associated with the amount of sunspots on its surface. These dark regions, some of which can exceed the size of the Earth, are caused by solar flares that generate strong magnetic fields. Based on the recordings from the INTERMAGNET observatories and the planetary geomagnetic indices from January 2023-April 2024, we performed the analysis of geomagnetic storms and selected the first three strongest events. Following the Fourier, wavelet and wavelet coherence analyses of geomagnetic data taken at one minute, for 20 observatories and comparing them with the physical parameters of solar activity, available on specialized websites, we exemplified in the paper the most relevant characteristics of geomagnetic storms in 2023 and early 2024. [ABSTRACT FROM AUTHOR]

We report a specular loss event of radiation belt electrons induced by a moderate geomagnetic storm on April 4, 2017, by using Van Allen Probe observations. During the initial phase, when the solar wind dynamic pressure (Pdyn) reached 12 nPa, the radiation belt electrons at Ek > ∼200 keV experienced a partial loss, followed by noticeable energy dispersion, which pronouncedly occurred at larger pitch angles on higher L shells. During the main phase, both probes witnessed a significant electron flux depletion at all energies from 54 to 2.6 MeV on the dusk-night side (MLT = magnetic local time around 20). Moreover, the corresponding phase space density (PSD) shows a local dip within L* = 4.44–4.87 (drift shell under adiabatic coordinate), which is not the outermost of L*, lasting for one pass (semi-period) of the spacecraft and quickly disappearing. By comparing the characteristics of electron loss in response to variations of the solar wind and geomagnetic indices, the movement of the estimated magnetopause location and the last closed drift shells, as well as the distribution of the plasma waves, we find that the partial dropout was essentially induced by the magnetopause shadowing effect, while the potential effect of the subsequent local PSD dip cannot be clearly explained by the present theory as far as we know. By showing the specular dropout event in the present work, we underline that the different loss effects should draw special attention from the space physics community. [ABSTRACT FROM AUTHOR]

Scientists have long studied the movement of earth's magnetic poles--not only because explorers & travelers depend on the poles for navigation since ancient times, but morerecently, we use them to calibrate things such as GPS. Besides the location & movement of the poles, the strength of earth's "protective" geomagnetic field has been important since mankind has used electronic technology. While these 2 phenomena (pole excursions aka movement & field strength) aren't well understood as to cause or predicted future behavior, scientists uniformly agree on 2 things: First, a "pole flip" (whether slow or fast) is believed to occur concomitantly (simultaneously) with a "field collapse." Secondly, as the field grows weaker, earth's technology becomes more vulnerable to solar flares, CME's (coronal mass ejections), and life on earth is less protected from cosmic radiation (a cancer risk), particularly satellites, and most-especially in the SAA (South Atlantic Anomaly) region. Thus, I revisit my prior research on this to seek help in assessing projections / predictions and taking precautionary steps to protect our technology & life on earth, as we know it--as we face a "trifecta" of a 'perfect storm': [[1]] our increased dependence on electronic technology (vulnerable to solar weather); [[2]] the eventual collapse of earth's 'protective' magnetic field; and, lastly, [[3]] occasional severe Carrington-class solar super storms, which impact GPS, satellites, and our fragile power & telecommunications systems. [ABSTRACT FROM AUTHOR]

The document provides abstracts for upcoming conferences in India and Italy organized by Biju Longhinos and Valentino Straser, respectively. It discusses theoretical frameworks for understanding Earth's energy budget and the effects of solar activity on seismicity and weather patterns. The text explores correlations between solar phenomena, earthquakes, hurricanes, and tornado outbreaks, suggesting potential electromagnetic and tectonic modulations. The research aims to investigate the complex interactions between space weather, seismic activity, and extreme weather events, highlighting the need for further study in these interconnected fields. [Extracted from the article]

The ring current, one of the most important current systems around the Earth, intensifies during geomagnetic storms and is believed to be the main reason for large-scale magnetic field perturbations in the geospace environment. Understanding how the ring current builds up and evolves during geomagnetic storms is of great importance not only for advancing the knowledge of the Sun-Earth system but also for improving the modeling capability of predicting hazardous space weather events. Focusing on the national strategic needs in the space weather prediction, in this study, we establish a ring current model named storm time ring current model (STRIM). The STRIM comprehensively embraces key physical processes in association with ring current dynamics, including plasma source injections from the nightside plasmasheet and transport around the Earth, charge-exchange with neutral hydrogens, Coulomb collisions with thermal plasma, wave-particle interactions, field line curvature scattering, and precipitation loss down to the upper atmosphere. The electric fields needed for particle motion can be optionally taken from empirical models or self-consistently calculated, while the magnetic field configuration is obtained from Tsyganenko 2005 model. Simulation results are verified against the published literature and validated with in-situ satellite or ground-based observations and are found to have the same high-level capability and fidelity as other well-known published models. We also discuss future tasks of fostering the model's performance and potential applications. [ABSTRACT FROM AUTHOR]

Ground magnetic field measurements are an important tool to determine the strength of space weather events in the terrestrial environment on local and global scales. For that purpose, geomagnetic baselines play a vital role as they describe typical quiet variations within geomagnetic data which allows the successive isolation of magnetic storm contributions. This work introduces an operational baseline derivation method to accurately assess then replace the amplitude of space weather events within high‐quality ground magnetic field measurements from magnetic observatories located in mid‐latitudes. A two‐step approach first identifies storm and disturbance intervals within the magnetic signal. Quiet variations, consistent with pre‐ and post‐disturbance periods, are then used to replace the signal during the identified intervals. The final baseline is validated through comparisons with existing methods and through demonstration during moderate and strong space weather events at 13 globally distributed observatories, demonstrating its ability to track quiet variations accurately while maintaining them during disturbances. This supports the application of the introduced baseline for geomagnetic field description and new magnetic index derivation for space weather event characterization with high spatio‐temporal resolution. As the method is deployable in near real‐time, it is suitable for operational environments. Plain Language Summary: This research article is about a new method to improve the measurements of space weather effects on Earth's magnetic field. Space weather can cause significant disturbances in Earth's magnetic field, which are measureable from ground magnetic observatories. The new method helps remove these disturbances from the ground magnetic field measurements by describing the quiet magnetic field variations. This is important for understanding space weather and its effects. The introduced method works in two steps. First, it identifies periods of space weather activity in the measurements. Then, it replaces those periods with data from calmer times before or after the event. We show that this method works well for observatories in mid‐latitude regions and can be deployed in near real‐time making it useable in operational environments. Key Points: A geomagnetic baseline method is proposed that can be deployed in operational (near‐) real‐time environmentsAn algorithm that identifies magnetic disturbances within geomagnetic field measurements is introducedPossible replacements for magnetic quiet variations during storm and disturbance periods are elaborated [ABSTRACT FROM AUTHOR]

Impacts of lower atmosphere forecast uncertainties on the Ionosphere‐Thermosphere (IT) system are investigated using the Whole Atmosphere Community Climate Model with Thermosphere and Ionosphere eXtension (WACCM‐X) for April 2010 and March 2013 geomagnetic storms. For each storm, a specified‐dynamics simulation (analysis run) is carried out by constraining the model dynamics using reanalysis data. Results of the analysis runs are used as initial conditions for forecast runs initialized on 20, 10, 5, 2, and 1 day before the storm onset time. The forecast runs show that errors in TEC compared to the analysis run appear in the equatorial region within 1–2 days after forecast starts with differences of about 10%. These discrepancies gradually expand to high‐latitudes after 10 days. These errors in TECs could be due to the deviations in the semidiurnal (SW2) and non‐migrating (DE3) tides that also occur within 1–2 days after forecast starts. SW2 and DE3 tides could modify the E‐region wind driven dynamo at low latitudes, affecting the vertical plasma drift in the F‐region, leading to the forecast errors in TEC. The TEC forecast errors at high‐latitudes could be due to the change in the column integrated O/N2, associated with tidal wind variations and resultant delayed change in vertical motions. The SW2 and DE3 tides can be affected by uncertainties in winds in the mesosphere and lower thermosphere (MLT) in the mid‐to‐high latitudes. The MLT wind uncertainties are correlated with gravity wave drag (GWD), suggesting that the uncertainties in GWD can be one of the major sources of IT forecast errors. Plain Language Summary: This study explores how the accuracy in predicting the lower atmospheric forcing can affect our ability to forecast the ionosphere‐thermosphere system in space weather, which is crucial for the operation of very low earth orbit satellites and the stability of communication and navigation systems. By using a state‐of‐the‐art numerical model, we attempt to simulate the effects of lower atmospheric forcing errors during the geomagnetic storm events in April 2010 and March 2013. We found that uncertainties in lower atmosphere forecasts lead to noticeable errors in predicting the distribution of electrons in the upper atmosphere within just 1–2 days. These uncertainties become larger as the forecast extends beyond 10 days, showing the significant impacts of the atmospheric waves on the predictions of the upper atmosphere. This research helps us understand where the forecast errors come from and how to improve the predictions of the ionosphere‐thermosphere system in space weather forecast. Key Points: Effects of lower atmosphere forecast uncertainties on the Ionosphere‐Thermosphere system are investigated for two geomagnetic stormsTotal Electron Content forecast errors start in the equatorial region within 1–2 days after and expand to high latitudes after 10 daysUncertainty in gravity wave drag can be one of the major sources of ionosphere‐thermosphere forecast errors [ABSTRACT FROM AUTHOR]

Space weather events, including solar flares, coronal mass ejections, and geomagnetic storms, have significant effects on various transportation systems. This review provides a comprehensive examination of the current understanding and future outlook of space weather effects on air, maritime, railway, and ground transportation. It explores the mechanisms through which space weather causes communication blackouts, satellite navigation failure, elevated cosmic radiation, and geomagnetically induced currents, leading to disruptions in transportation operations. Historical events are analyzed to underscore the diversity and severity of these impacts. Additionally, this review discusses the anticipated challenges posed by the upcoming solar maximum of Solar Cycle 25 and highlights the need for improved forecasting, mitigation strategies, and resilient infrastructure to safeguard transportation systems against space weather threats. By integrating findings from recent studies and historical data, this review aims to enhance the preparedness and response strategies of the transportation sector in the face of evolving space weather risks. Plain Language Summary: Space weather, which includes events like solar flares, coronal mass ejections, and geomagnetic storms, can seriously affect various transportation systems. This review thoroughly examines how these space weather phenomena impact air, maritime, railway, and ground transportation. It explains how space weather events can cause problems such as communication blackouts, failure of satellite navigation systems, increased levels of cosmic radiation, and geomagnetically induced currents. These issues can disrupt transportation operations significantly. The review looks at past events to show the range and seriousness of these impacts. It also discusses the upcoming solar maximum of Solar Cycle 25 and the challenges it may bring. The review emphasizes the need for better forecasting methods, effective mitigation strategies, and stronger infrastructure to protect transportation systems from space weather threats. By combining recent research and historical data, this review aims to improve how the transportation sector prepares for and responds to the risks posed by space weather. This is crucial for ensuring that transportation systems remain functional and safe despite the challenges posed by space weather. Key Points: Mechanisms of space weather‐caused disruptions in critical infrastructure are identifiedThe effects of space weather on various transportation modes are examinedRecommendations for mitigating space weather effects on transportation systems are discussed [ABSTRACT FROM AUTHOR]

Relativistic electrons cause internal charging on satellites and are a significant space weather hazard. In this study we analyze approximately 20 years of data from the US Global Positioning System (GPS) satellite NS41 to determine the conditions associated with the largest daily averaged fluxes of E $E$ = 2.0 MeV relativistic electrons. The largest flux events at L $L$ = 4.5 and L $L$ = 6.5 were associated with moderate to strong CME‐driven geomagnetic storms. However, the majority of the 50 largest flux events at L $L$ = 4.5 (30 out of 50) and L $L$ = 6.5 (37 out of 50) were associated with high speed solar wind streams from coronal holes. Both solar drivers are thus very important for relativistic electron flux enhancements in GPS orbit. The 1 in 3 year flux level was not exceeded following any of the 15 largest geomagnetic storms as monitored by the Dst $Dst$ index, showing that the largest geomagnetic storms, most often associated with extreme space weather, do not result in significantly larger relativistic electron flux events in GPS orbit. Plain Language Summary: Very high energy electrons can damage spacecraft and are a potential risk to humans in space. Here we use approximately 20 years of data from the US Global Positioning System (GPS) satellite NS41 to determine the conditions associated with the production of the largest numbers of these, so‐called, "killer" electrons. The largest events in the outer radiation belt, a donut‐shape zone of very high energy electrons encircling the Earth, were caused by large explosions from the Sun's outer atmosphere, known as coronal mass ejections. However, the majority of the 50 largest events were associated high speed streams of energetic electrons emanating from darker and cooler areas in the Sun's outer atmosphere, known as coronal holes. The largest events were associated with moderate to strong geomagnetic storms. In contrast, the largest geomagnetic storms, most often associated with extreme space weather, did not result in significantly larger high energy electron flux events in GPS orbit. Key Points: The largest fluxes of E = 2.0 MeV electrons in GPS orbit were associated with moderate to strong CME‐driven geomagnetic stormsThe majority of the 50 largest flux events at L = 4.5 (30 out of 50) and L = 6.5 (37 out of 50) were associated with high speed streamsThe 1 in 3 year flux levels at L = 4.5 and 6.5 were not exceeded following any of the 15 largest geomagnetic storms [ABSTRACT FROM AUTHOR]

In this study, we developed a novel deep learning model to predict the disturbance storm time (Dst) index 1–4 hr ahead. We also employed the Monte Carlo (MC) dropout technique to estimate the uncertainty and provide the prediction interval by introducing a recalibration factor. The proposed model achieves excellent scalability by extracting representative embeddings from the Dst index time series through an encoder‐decoder framework and integrating these with external solar wind parameters via a prediction network. We utilized magnetic storm data from 1998 to 2018 to evaluate the performance of the prediction model. Experimental results indicate that the proposed model reduces root mean square errors (RMSE) and improves the coefficient of determination (R2) compared to existing methods. Quantitative uncertainty analysis demonstrates that the prediction interval is reliable in most cases. The percent distribution across test storms by comparing the uncertainty‐based prediction of the minimum peak with the mean prediction indicates the probabilistic forecast model is competitive. Plain Language Summary: Geomagnetic storms can negatively affect both space and ground‐based electronic devices. We have developed an innovative deep learning model capable of predicting the Dst index 1–4 hr ahead of time. Additionally, the model estimates uncertainty and calculates how well it covers the prediction interval using the MC dropout technique. Using data during magnetic storms from 1998 to 2018, we analyzed the performance of our prediction model. Our results ingdicate that the model offers high prediction accuracy with minimal errors and dependable uncertainty estimates, enabling effective anomaly detection during storms. Key Points: The proposed model provides a comprehensive assessment of quantitative uncertainty, indicating the predictive interval is reliableThe prediction model achieves an average decrease of approximately 32% in RMSEs compared to the persistence modelUncertainty‐based prediction of minimum peak achieves an average improvement of ∼16% by comparison with the mean prediction [ABSTRACT FROM AUTHOR]

Geomagnetic storms affect Earth in various severe ways, including damaging satellites, disrupting power grids, and inducing prompt penetration electric fields (PPEF) through Joule heating in the auroral region. They also cause disturbance dynamo electric fields (DDEF), generate or suppress equatorial plasma bubbles (EPBs), and lead to other significant effects. The extreme geomagnetic storm on 10 May 2024, altered the dynamics of the ionosphere. The ionospheric response was investigated in this study. Our methodology utilized a combined data set, including GNSS receivers in the Latin American sector, and data from ionosondes in São Luis (SALU) and Cachoeira Paulista (CHPI). CHPI also features a Fabry‐Pérot interferometer (FPI) and an All‐Sky Imager (ASI). Super EPB was observed in the American sector. This structure drifted westward at a velocity of ∼140 m/s and had a large latitudinal extension, reaching about 36° geomagnetic latitude, this corresponds to an apex height of around 4,500 km. The depletion lasted for a long duration of 12 hr, from 22:30 to 10:30 UT. The geomagnetic storm caused a super fountain effect, propelling plasma from the equator to a distance of ∼35° latitude, and depositing high‐density plasma on the crest of the equatorial ionization anomaly (EIA). Plain Language Summary: On 10 May 2024, an extreme geomagnetic storm significantly impacted the ionosphere over South America. Data from satellite receivers, ionosondes, and All‐Sky Imagers were combined to analyze the ionospheric changes during this event. A unique super equatorial plasma bubble (EPB) formed and persisted for 12 hr, extending across a latitudinal range (36° MLAT). The geomagnetic storm also generated a super fountain effect, causing poleward movement of the plasma crests to latitudes exceeding their typical positions (>20°). This study investigates the formation and dynamics of these ionospheric structures, along with the overall impact of extreme geomagnetic storms on the ionosphere. The direction of the storm‐induced electric field was identified as the key driver behind these ionospheric changes. Our findings emphasize the significant alterations that storms can impose on the ionosphere. Key Points: Formation of a long‐lasting super equatorial plasma bubble, propagating westwardDevelopment of an intensified nighttime super‐fountain effect, with the equatorial ionization anomaly crests expanding polewardOnset of a strong positive ionospheric storm, characterized by a significant increase in plasma density [ABSTRACT FROM AUTHOR]

Thermospheric density influences the atmospheric drag and is crucial for space missions. This paper introduces a global thermospheric density prediction framework based on a deep evidential method. The proposed framework predicts thermospheric density at the required time and geographic position with given geomagnetic and solar indices. It is called global to differentiate it from existing research that only predicts density along a satellite orbit. Through the deep evidential method, we assimilate data from various sources including solar and geomagnetic conditions, accelerometer‐derived density data, and empirical models including the Jacchia‐Bowman model (JB‐2008) and the Naval Research Laboratory Mass Spectrometer and Incoherent Scatter Radar Extended (NRLMSISE‐00) model. The framework is investigated on five test cases along various satellites from 2003 to 2015 involving geomagnetic storms with Disturbance Storm Time (Dst) values smaller than −50 nT $\mathrm{n}\mathrm{T}$. Results show that the proposed framework can generate density with higher accuracy than the two empirical models. It can also obtain reliable uncertainty estimations. Global density estimations at altitudes from 200 to 550 km are also presented and compared with empirical models on both quiet and storm conditions. Plain Language Summary: Thermospheric density affects atmospheric drag, which is important for many space missions. This paper presents a global thermospheric density prediction framework based on a deep evidential method. It incorporates data from empirical models JB‐2008 and NRLMSISE‐00, solar and geomagnetic indices, and density derived from satellite accelerometers. Test cases are designed from 2003 to 2015 under quiet and storm conditions based on various satellites. The proposed framework demonstrates higher accuracy and reliable uncertainty estimates compared to the empirical models. Key Points: A global thermospheric density prediction framework is presented based on a deep evidential methodThe proposed framework predicts thermospheric density at the required time and geographic position with given geomagnetic and solar indicesThe proposed framework predicts thermospheric density more accurately than two empirical models and provides reliable uncertainty estimations [ABSTRACT FROM AUTHOR]

This study investigates the Brazilian low‐latitude ionospheric response to CIR/HSS‐driven geomagnetic storms during the declining phase of solar cycle 24, from 2016 to 2017. In this period the geomagnetic storms were mostly moderate, SymHmin ≈ −72 nT, AEmax ≈ 1580 nT, Vswmax ≈ 690 km/s and lasted, on average, for 6 days. We analyze the variations in Vertical Total Electron Content (VTEC) at three representative regions: bele, over the equatorial region; boav and cuib, at the northern and southern crests of the Equatorial Ionization Anomaly. Our findings reveal the role of High‐Speed Solar Wind Streams and Corotating Interaction Region—driven geomagnetic storms. The VTEC intensifications were up to 30 TECu, during the daytime and nighttime. Additionally, three categories of nighttime enhancements were observed and analyzed with distinct characteristics and levels of pre‐reversal strengthening; Depletions up to 20 TECu also occurred during the day and nighttime. The delay between the storm commencement and the positive and negative variations were, on average, 7 and 20 hours, respectively. We discuss the Prompt Penetration Electric Fields and Disturbance Dynamo Electric Fields following the magnetic reconnection between Earth's and interplanetary magnetic field, using observational data and modeling. Furthermore, this study presents catalogs of low‐latitude ionospheric storms, providing detailed information for space weather applications and ionospheric modeling. Plain Language Summary: This study examines the impact of solar wind on the low‐latitude ionosphere, in Brazilian longitudinal sector, during the descending phase of the SC 24, 2016/2017. Specifically, we focused on High‐Speed Solar wind Streams (HSS) and Corotating Interaction Regions (CIRs) that can cause disturbances in the Earth's magnetic field, leading to weak‐to‐moderate geomagnetic storms. Our findings show that these disturbances can affect the low‐latitude ionosphere for several days. By analyzing the variations in the Vertical Total Electron Content (VTEC), we found that remarkable increases occur during the recovery phase of these storms, observed at the crests of the EIA. This study provides new insights into the effects of the solar wind on the Earth's atmosphere during moderate solar activity which can be of interest for space weather applications. Key Points: Statistical study on the low‐latitude Vertical Total Electron Content in Brazilian longitudinal sector during the declining phase of SC 24 and Catalogs with the main resultsLow latitude daytime and nighttime ionospheric variations were observed up to 30 TECu and −20 TECuEffects of prompt penetration electric fields and disturbance dynamo electric fields in the Brazilian low latitude ionosphere: three case studies [ABSTRACT FROM AUTHOR]

The Earth's radiation belts are usually composed of an inner and an outer zone. Previous studies have reported a third belt of ultra‐relativistic electrons, but the mechanism requires to be further clarified. Here we report a very interesting feature of 3.4−6.3 $3.4-6.3$ MeV electrons during two storms in October 2018. During the October 7 storm the electrons in the region L≈3.5−5.0 $L\approx 3.5-5.0$ were quickly scattered by EMIC waves, leading to a storage ring left between L≈3.0−3.5 $L\approx 3.0-3.5$. Over the following days, due to the chorus‐driven acceleration, electron fluxes significantly increased in the region L>4 $L > 4$, consequently allowing for a three‐belt structure. During the October 13 storm the electrons in the region L>5 $L > 5$ were swept away by EMIC waves, leaving a narrow outer radiation belt confined within the region L≈4−5 $L\approx 4-5$ for several days. Numerical calculations demonstrate that the EMIC‐driven loss and chorus‐induced acceleration can account for the formation and evolution of the third‐belt morphology. Plain Language Summary: The Earth's electron radiation belts are usually composed of two high‐flux zones called the inner and outer belts, which are separated by a low‐flux slot region. However, previous studies have found that ultra‐relativistic (kinetic energy Ek>3 ${E}_{\mathrm{k}} > 3$ MeV) electrons sometimes exhibit a three‐belt morphology. Although some theories have been proposed, the mechanism underlying this rare phenomenon still requires further elucidation. Here we report a very interesting feature of 3.4–6.3 MeV electrons during two geomagnetic storms in October 2018. Prior to the first storm on October 7, the outer belt was present between the magnetic L $L$‐shell 3.0–5.0. During the storm main phase, electrons in the region L≈3.5−5.0 $L\approx 3.5-5.0$ were quickly lost by electromagnetic ion cyclotron (EMIC) waves, leaving a high‐flux zone between L≈3.0−3.5 $L\approx 3.0-3.5$. Over the following days, electrons in the region L>4 $L > 4$ were accelerated by chorus waves, consequently allowing for a three‐belt structure. During the second storm on October 13, electrons in the region L>5 $L > 5$ were swept away by EMIC waves, leaving a narrow outer belt confined within the region L≈4−5 $L\approx 4-5$ for several days. Numerical calculations demonstrate that the EMIC‐driven loss and chorus‐induced acceleration can account for the formation and evolution of the third‐belt morphology. Key Points: Ultra‐relativistic electrons exhibited three‐belt morphologies during storms in October 2018, corresponding to enhanced EMIC/chorus wavesCalculations show that electron loss/acceleration timescales induced by EMIC/chorus are about 0.01/10 days, comparable to observationsThe combined role of electromagnetic ion cyclotron (EMIC) and chorus waves can explain the formation and evolution of the three‐belt morphology [ABSTRACT FROM AUTHOR]

The May 2024 super storm is one of the strongest geomagnetic storms during the past 20 years. One of the most remarkable ionospheric responses to this event over East and Southeast Asia is the complex ionospheric fluctuations following the storm commencement. The fluctuations created multiple oscillations of total electron content (TEC) embedded in the diurnal variation, with amplitudes up to 10 TECu. Along the same latitude, the fluctuations were nearly synchronized over a wide longitude span up to 35°. In the meridional direction, the fluctuations over low latitudes were the most significant and complex, which contained two main components, the poleward extending oscillations originated from the magnetic equator, and the equatorward propagating traveling ionospheric disturbances (TIDs) from high latitudes. The TIDs likely occurred around the globe. The storm‐time interplanetary electric fields penetrating into equatorial latitudes of the ionosphere and the auroral energy input were suggested to drive the poleward extending oscillations and the equatorward TIDs, respectively. Plain Language Summary: The ionospheric responses to strong geomagnetic storms are mainly in the form of global or hemispheric scale plasma density enhancement or suppression, termed as positive or negative ionospheric storms, respectively. Previous studies have also reported fine‐scale ionospheric structures during geomagnetic storms, which were manifested as wavelike fluctuations in TEC. Multiple mechanisms were proposed to be responsible for the TEC fluctuations, including the magnetospheric compression effect, storm‐time penetration electric field, refilling process linked with plasma pressure, and traveling ionospheric disturbances triggered from high latitude and polar regions. During the May 2024 super storm, complex ionospheric fluctuations consisting of two major components, that is, poleward extending fluctuations originated from the magnetic equator and equatorward traveling oscillations from high latitude and polar regions were observed over East and Southeast Asia. It is important to figure out what mechanisms could dominate the generation and evolution of complex fluctuations over specific regions. Based on the TEC continuously measured along dense observational chains, in combination with multiple other types of observations, the characteristics and possible mechanisms of the complex ionospheric fluctuations are investigated. Key Points: Complex ionospheric fluctuations consisting of poleward extending and equatorward traveling disturbances were identified during super geomagnetic stormThe poleward oscillations were synchronized over a wide longitude and driven by multiple penetrations of electric fieldsThe equatorward traveling disturbances likely occurred around the globe that could be due to auroral energy input [ABSTRACT FROM AUTHOR]

A train of large‐scale polar cap patches was observed in the ionosphere during a period of southward interplanetary magnetic field (IMF) during the main phase of a moderate geomagnetic storm. The patches were sequentially detached from a dayside storm enhanced density plume through cusp dynamics due to pulsed enhancement of the dayside magnetic reconnection rate, suggested by the increase of the Kan‐Lee electric field and cross polar cap potential. After formation and IMF By duskward turning, the patches propagated obliquely like "waves" in the polar cap toward the dusk sector, and exited the polar cap over a wide magnetic local time (MLT) region (18–24 MLT). Simulations under a strongly southward IMF Bz and duskward IMF By show that the magnetotail magnetic reconnection occurs over a broad MLT range. Such a tail reconnection modulates the evolution of the patches. Key Points: A train of patches exhibits the "wave‐like" evolution associated with the magnetopause reconnection and magnetotail reconnectionThe duskward tilted convection pattern, impacted by IMF By, partially contributes to patch spatial spread toward the nightside sectorThis work provides the evidence for extended magnetic reconnection in the dusk magnetotail [ABSTRACT FROM AUTHOR]

D‐region effect of intense storm of 23 March (Dst = −163 nT) and super storm of 23 April 2023 (Dst = −212 nT) have been investigated using VTX and NWC transmitter signals recorded at low latitude station Dehradun (DDN; 30.31°N, 78.03°E), India. During March storm on 23 March, amplitude anomalies of +2.92 (NWC) and +1.91 dB (VTX) were observed. April storm showed amplitude anomalies of −9.41 (NWC) and −2.68 dB (VTX) on 23 April. Long Wave Propagation Capability code (LWPC) has been used to model signal anomalies to obtain D‐region Very low frequency (VLF) reference height (H′) and electron density gradient (β). During March storm, NWC‐Dehradun path showed a decrease in H′ by 12.04 km and an increase in β by 0.301 km−1, while VTX‐Dehradun path showed an increase in H′ by 0.07 km and β by 0.032 km−1 on 23 March. During April storm, VTX‐Dehradun path showed increase in H′ by 0.315 km and an increase in β by 0.024 km−1, while H′ increased by 2.91 km and β by 0.23 km−1 for NWC—Dehradun path on 23 April. Wavelet analysis of VLF anomalies showed signatures of atmospheric gravity waves of periods between 30 and 100 min during both storms associated with joule heating in the high/auroral latitudes. Results suggest that storm time prompt penetration (PP) of electric fields has contributed to VLF signal anomalies during April storm's main phase, which is also supported by PP Equatorial Electric Field Model run for the location of DDN station. Key Points: Very low frequency (VLF) anomalies from both the March and April 2023 storms are associated with atmospheric gravity waves (AGWs) with periods of 30–100 minAGWs at low latitudes are found to be linked to Joule heating in the auroral/high‐latitude regions during the stormsPrompt penetration of electric fields during storm time is reported to have caused D‐region changes during main phase of April superstorm [ABSTRACT FROM AUTHOR]

We investigate the dynamics of relativistic electrons in the Earth's outer radiation belt by analyzing the interplay of several key physical processes: electron losses due to pitch angle scattering from electromagnetic ion cyclotron (EMIC) waves and chorus waves, and electron flux increases from chorus wave‐driven acceleration of ∼ ${\sim} $100–300 keV seed electrons injected from the plasma sheet. We examine a weak geomagnetic storm on 17 April 2021, using observations from various spacecraft, including GOES, Van Allen Probes, ERG/ARASE, MMS, ELFIN, and POES. Despite strong EMIC‐ and chorus wave‐driven electron precipitation in the outer radiation belt, trapped 0.1–1.5 MeV electron fluxes actually increased. We use theoretical estimates of electron quasi‐linear diffusion rates by chorus and EMIC waves, based on statistics of their wave power distribution, to examine the role of those waves in the observed relativistic electron flux variations. We find that a significant supply of 100–300 keV electrons by plasma sheet injections together with chorus wave‐driven acceleration can overcome the rate of chorus and EMIC wave‐driven electron losses through pitch angle scattering toward the loss cone, explaining the observed net increase in electron fluxes. Our study emphasizes the importance of simultaneously taking into account resonant wave‐particle interactions and modeled local energy gradients of electron phase space density following injections, to accurately forecast the dynamical evolution of trapped electron fluxes. Key Points: Multi‐satellite observations of EMIC and chorus waves and injections are used to investigate their relative importance in electron dynamicsWe show that chorus‐driven acceleration during plasma sheet injections can overcome EMIC‐driven lossesWe develop an analytical model of relativistic electron flux variations subject to acceleration and losses [ABSTRACT FROM AUTHOR]

Two interacting high‐speed solar wind streams (HSSs) and associated stream interaction regions (SIR) caused a moderate geomagnetic storm during 14–20 March 2016. The spatio‐temporal evolution of the total electron content (TEC) during the storm is studied by using Global Navigation Satellite System (GNSS) data. The moderate storm caused significant and long‐lasting changes on TEC within the polar cap (70° ${}^{\circ}$–90° ${}^{\circ}$ MLAT), at auroral and sub‐auroral latitudes (60° ${}^{\circ}$–70° ${}^{\circ}$ MLAT), and at mid‐latitudes (40° ${}^{\circ}$–60° ${}^{\circ}$ MLAT). A 25%–50% depletion in TEC was observed for six days in the day, dusk and dawn sectors in the polar cap region and in the day and dusk sectors at the auroral and sub‐auroral latitudes. Sub‐auroral polarization streams observed by the Defense Meteorological Satellite Program satellite contributed to the sub‐auroral dusk TEC decreases. At mid‐latitudes, TEC depletion was observed in all local time sectors 21 hr after the storm onset. It is suggested that ion‐neutral frictional heating causes the TEC depletions, which is further supported by the observed spatial correlation between TEC depletions and ∑ $\sum $O/N2 decreases at mid‐latitudes observed by TIMED/GUVI. The storm induced a prolonged positive phase at mid‐latitudes lasting 9 hr. In the polar cap, enhancements of TEC up to 200% were caused by polar cap patches. TEC increases were the dominant feature in the night and morning sectors within the auroral oval because of particle precipitation and resulted up to regionally averaged 6 TECU (200%) increases. Plain Language Summary: Interaction of solar wind with the Earth's magnetosphere can cause perturbations to the geomagnetic field, known as geomagnetic storms. This study presents the ionospheric response to a moderate geomagnetic storm during 14–20 March 2016 caused by high‐speed solar wind streams, characterized by its high velocity > ${ >} $500 km/s. Total electron content (TEC) maps from Global Navigation Satellite System were used to study the electron density variations during the storm. With the commencement of the storm, a 25%–50% decrease in TEC was observed on the dayside, duskside and dawn side in the polar cap region. In the auroral and sub‐auroral region, the storm caused a depletion on the dayside and duskside. Strong auroral precipitation during the storm caused a 200% increase in TEC in the night side auroral oval. The initial response at mid latitudes was a long duration enhancement in TEC that lasted for 9 hr followed by a decrease in TEC that persisted till 20 March. The TEC depletion at mid latitudes shows spatial correlation with neutral composition changes agreeing with previous studies. The composition change originates from high latitudes, where the atmosphere is heated because of strong electric fields. Key Points: High speed stream/SIR‐driven moderate storm drives 6 days long depletion in total electron content (TEC) reaching at least 25% during each day from polar to mid latitudesMid‐latitude TEC depletions in late morning correlate spatially with regions of increased ΣO/N2 as measured by TIMED/Global Ultra Violet ImagerIn the nightside auroral oval TEC increases reaching 6 TECU (200%) and shows temporal correlation with the Auroral electrojet index [ABSTRACT FROM AUTHOR]

On 10 May 2024, a super geomagnetic storm occurred with a minimum Dst index of −412 nT. This study investigates the behavior of the ionospheric radial current (IRC) during the main phase of this storm using data from Swarm A and simulations from the Thermosphere‐Ionosphere Electrodynamics General Circulation Model (TIEGCM). At dawn, the IRC exhibits distinct temporal variations: a strong outward flow of 14 nA/m2 between 18:00 and 20:00 UT and an inward flow of −15 nA/m2 by 24:00 UT. At dusk, the IRC starts with an inward value of −6 nA/m2 and rapidly reverses to an outward flow peaking at 15 nA/m2 between 22:00 and 24:00 UT. The dawn‐dusk asymmetry of the IRC is primarily influenced by the merging electric field (Em). Increasing Em penetrates to low latitudes, establishing an eastward (dusk) or westward (dawn) electric field and enhancing the outward (dusk) or inward (dawn) IRC through meridional Hall currents. Model results indicate that the strong polarity changes in dawn IRC are linked to local disturbed zonal winds (Δuy ${{\Delta }u}_{y}$). Which are eastward at dawn and westward at other magnetic local times (MLT). The eastward/westward Δuy ${{\Delta }u}_{y}$ generate outward/inward F‐layer dynamo currents, driving the disturbed vertical electric field (ΔEz ${{\Delta }E}_{z}$) in opposite direction. The significant outward reversal of dusk ∆IRC could be attribute to the rapid enhancement of disturbed Pedersen conductivity (Δσp ${{\Delta }\sigma }_{p}$). Due to nonzero geomagnetic declination, eastward/westward Δuy ${{\Delta }u}_{y}$ corresponds to an increase/decrease in Δσp ${{\Delta }\sigma }_{p}$. Key Points: Ionospheric radial current (IRC) has an extreme response of approximately 15 nA/m2 to the super stormThe increase of Em can enhance the outward/inward IRC at dawn/duskΔuy ${{\Delta }u}_{y}$ (Δσp ${{\Delta }\sigma }_{p}$) is key in the polarity changes of IRC at dawn (dusk) [ABSTRACT FROM AUTHOR]

[During intense geomagnetic storms, the rapid and significant production of nitric oxide (NO) followed by its associated infrared radiative emission in lower thermosphere contributes crucially to the energetics of the upper atmosphere. This makes NO infrared radiative cooling a very important phenomenon which needs to be considered for accurate density forecasting in thermosphere. This study reports the investigation of variations in thermospheric density, and NO radiative cooling during the recent geomagnetic superstorm of May 2024. A very rare post‐storm thermospheric density depletion of about −23% on May 12 was observed by Swarm‐C in northern hemisphere in comparison to the prestorm condition on May 9. This overcooling was observed despite the continuous enhancement in solar EUV (24–36 nm) flux throughout the event. The thermospheric NO infrared radiative emission in the recovery phase of the storm is likely to be the plausible cause for this observed post‐storm density depletion. Our analysis also suggests an all time high thermospheric NO radiative cooling flux up to 11.84 ergs/cm2 ${\text{ergs/cm}}^{2}$/sec during May 2024 geomagnetic superstorm, which has also been compared with famous Halloween storms of October 2003]. Plain Language Summary: The changing heat budget of upper atmosphere due to enhanced Joule heating, energetic particle precipitations, and NO infrared radiative cooling during geomagnetic storms may also modulate other atmospheric and ionospheric parameters that indirectly affect human life at the surface. Some examples are, thermospheric density and associated Lower Earth Orbit (LEO) satellite drags (which are particularly used for geophysical imaging), GPS navigation, exposure of thermospheric particles near ISS (International Space stations), etc. All these aspects need to be considered for a better space weather future. In this study, the variation in thermospheric density, and thermospheric NO radiative cooling have been investigated during the recent geomagnetic superstorm of May 2024. This study infers that the very enhanced NO radiative cooling in the recovery phase of this storm may have also contributed to the thermospheric density depletion in the post‐storm periods. The NO radiative cooling during this storm has also been compared with Halloween storms of October 2003. Key Points: An all time high thermospheric NO radiative cooling flux is observed during the recent May 2024 geomagnetic superstormA potential post‐storm thermospheric overcooling is observed by TIMED/SABER, Swarm‐A, ‐B, and ‐C during this superstormA comparison of thermospheric NO radiative cooling is presented between the Halloween storms of 2003, and May 2024 geomagnetic superstorm [ABSTRACT FROM AUTHOR]

Following the auroral substorm onset, the active aurora undergoes expansion, which can vary in spatial and temporal extent. The spatiotemporal development of the expansion phase active aurora is controlled by new auroral intensifications that often follow the initial onset. Using seven examples, we investigate the nature of these new auroral intensifications and address a question: are they new auroral onsets, that is, "successive onsets" or poleward‐boundary intensifications (PBIs) and ensuing auroral streamers? We observed events that included both types of auroral features—successive onsets and PBIs—and their combinations. For multiple‐onset substorms, successive onsets may occur eastward, westward, and poleward of the initial onset, resulting in a diverse range of expansion phase spatial extent and durations. Single‐onset substorms show only one auroral onset, but their spatiotemporal development can resemble that of multiple‐onset substorms. However, the additional activations are mainly PBIs and subsequent streamers. In some cases, PBIs undergo explosion, leading to a rapid poleward and azimuthal expansion of the aurora, resembling the auroral substorm onset. A prolonged sequence of PBIs and its longitudinal extension can contribute significantly to the spatiotemporal development of substorms expansion phase. Results suggest that post‐onset flow channels drive the spatiotemporal development of the substorm expansion phase by (a) triggering successive onsets and (b) inducing bursts of PBIs and their prolonged sequence. We speculate that post‐onset flow channels likely originate from the polar cap, but more evaluation is required. Our findings highlight the significance of examining imager data before solely relying on magnetometers to identify substorm onsets. Key Points: Successive onsets, often preceded by post‐onset streamers, cause diverse range of expansion phase coverage and durationsA prolonged sequence of poleward‐boundary intensifications and auroral streamers play a crucial role in driving spatiotemporal development of substorm expansion phasePost‐onset flow channels play an important role in spatiotemporal development of substorm expansion phase [ABSTRACT FROM AUTHOR]