Storm Main Phase Research Articles

Geoelectric fields and geomagnetically induced currents during the April 23–24, 2023 geomagnetic storm

We present a study on the dynamical variations of geoelectric fields E during the intense geomagnetic storm of April 23–24, 2023. The storm is caused by the interplanetary counterpart of a coronal mass ejection erupted from the Sun in association with an M1.7 X-ray flare. The GeoElectric Dynamic Mapping (GEDMap) code is applied to develop spatial E maps using magnetometer data from 29 observatories distributed across northern Europe. The code has been applied during local nighttime and morningtime intense substorms which occurred during the storm main phase. The maps show intensifications and strong variability of the E-fields during the substorm events. In particular, the morningtime event is associated with a significant variability in the E-field direction. Using the computed E-fields, we determined geomagnetically induced currents (GICs) at the sub-auroral station Mäntsälä. The modeled GIC values exhibit significant correlation (correlation coefficients r=0.73−0.76\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$r=0.73-0.76$$\\end{document}) with the observed values. The performed E-field mapping provides a basis for the further determination of GICs in selected locations not covered by magnetometers and can be useful in understanding the GIC variability during magnetic storms and substorms.

Interplanetary Causes and Impacts of the 2024 May Superstorm on the Geosphere: An Overview

The recent superstorm of 2024 May 10–11 is the second largest geomagnetic storm in the space age and the only one that has simultaneous interplanetary data (there were no interplanetary data for the 1989 March storm). The May superstorm was characterized by a sudden impulse (SI+) amplitude of +88 nT, followed by a three-step storm main-phase development, which had a total duration of ∼9 hr. The cause of the first storm main phase with a peak SYM-H intensity of −183 nT was a fast-forward interplanetary shock (magnetosonic Mach number M ms ∼ 7.2) and an interplanetary sheath with a southward interplanetary magnetic field component B s of ∼40 nT. The cause of the second storm's main phase with an SYM-H intensity of −354 nT was a deepening of the sheath B s to ∼43 nT. A magnetosonic wave (M ms ∼ 0.6) compressed the sheath to a high magnetic field strength of ∼71 nT. Intensified B s of ∼48 nT were the cause of the third and most intense storm main phase, with an SYM-H intensity of −518 nT. Three magnetic cloud events with B s fields of ∼25–40 nT occurred in the storm recovery phase, lengthening the recovery to ∼2.8 days. At geosynchronous orbit, ∼76 keV to ∼1.5 MeV electrons exhibited ∼1–3 orders of magnitude flux decreases following the shock/sheath impingement onto the magnetosphere. The cosmic-ray decreases at Dome C, Antarctica (effective vertical cutoff rigidity <0.01 GV) and Oulu, Finland (rigidity ∼0.8 GV) were ∼17% and ∼11%, respectively, relative to quiet-time values. Strong ionospheric current flows resulted in extreme geomagnetically induced currents of ∼30–40 A in the subauroral region. The storm period is characterized by strong polar-region field-aligned currents, with ∼10 times intensification during the main phase and equatorward expansion down to ∼50° geomagnetic (altitude-adjusted) latitude.

Rapid Geomagnetic Variations During High‐Speed Stream, Sheath and Magnetic Cloud‐Driven Geomagnetic Storms From 1996 to 2023

AbstractThe most detrimental geomagnetically induced currents (GICs) documented to date have all taken place during geomagnetic storms. Yet, the probability of GICs throughout geomagnetic storms driven by different solar wind transients, such as high‐speed streams/stream interaction regions (HSS/SIR) or interplanetary coronal mass ejection (ICME) sheaths and magnetic clouds (MC), is poorly understood. We present an algorithm to detect geomagnetic storms and storm phases, resulting in a catalog of 755 geomagnetic storms from January 1996 to June 2023 with the solar wind drivers. Using these storms and the IMAGE magnetometer network, we study the temporal and spatial evolution of spikes in the time derivative of the horizontal component of the external magnetic field, , greater than 0.5 nT/s during geomagnetic storms driven by HSS/SIR, sheaths and MCs. Spikes occur more often toward the end of the storm main phase for HSS/SIR and MC‐driven storms, while sheaths have spikes throughout the entire main phase. During the main phase most spikes occur in the morning sector around 05 magnetic local time (MLT) and the extent in MLT is narrowest for MCs and widest for sheaths. However, spikes in the pre‐midnight sector during the main and recovery phases are most prominent for HSS/SIR‐driven storms. During the storm sudden commencement (SSC), three MLT hotspots exist, the post‐midnight at 04 MLT, pre‐noon at 09 MLT and afternoon at 15 MLT. The pre‐noon hotspot has the highest probability of spikes and the widest extent in magnetic latitude.

The April 2023 SYM‐H = −233 nT Geomagnetic Storm: A Classical Event

AbstractThe 23–24 April 2023 double‐peak (SYM‐H intensities of −179 and −233 nT) intense geomagnetic storm was caused by interplanetary magnetic field southward component Bs associated with an interplanetary fast‐forward shock‐preceded sheath (Bs of 25 nT), followed by a magnetic cloud (MC) (Bs of 33 nT), respectively. These interplanetary structures were led by a coronal mass ejection erupted from the Sun in association with an M1.7 X‐ray flare. At the center of the MC, the plasma density exhibited an order of magnitude decrease, leading to a sub‐Alfvénic solar wind interval for ∼2.1 hr. Ionospheric Joule heating accounted for a significant part (∼81%) of the magnetospheric energy dissipation during the storm main phase. Equal amount of Joule heating in the dayside and nightside ionosphere is consistent with the observed intense and global‐scale DP2 (disturbance polar) currents during the storm main phase. The sub‐Alfvénic solar wind is associated with disappearance of substorms, a sharp decrease in Joule heating dissipation, and reduction in electromagnetic ion cyclotron wave amplitude. The shock/sheath compression of the magnetosphere led to relativistic electron flux losses in the outer radiation belt between L* = 3.5 and 5.5. Relativistic electron flux enhancements were detected in the lower L* ≤ 3.5 region during the storm main and recovery phases. Equatorial ionospheric plasma anomaly structures are found to be modulated by the prompt penetration electric fields. Around the anomaly crests, plasma density at ∼470 km altitude and altitude‐integrated ionospheric total electron content are found to increase by ∼60% and ∼80%, with ∼33% and ∼67% increases in their latitudinal extents compared to their quiet‐time values, respectively.

Low-latitude ionospheric responses and positioning performance of ground GNSS associated with the geomagnetic storm on March 13–14, 2022

Interplanetary coronal mass ejections (ICMEs) and the driven geomagnetic storms have a profound influence on the ionosphere, potentially leading to a degradation in positioning performance. In this study, we made a comprehensive analysis of the entire process of the impact of a typical ICME and its driven geomagnetic storm on the low-latitude ionosphere during March 13–14, 2022 (π-day storm) and the positioning performance of Global Navigation Satellite System (GNSS). During the passage of the ICME event, significant ionospheric scintillation, and TEC (total electron content) disturbances were observed in the low-latitude Hong Kong region. The ICME sheath region intensively compressed the magnetosphere via solar wind dynamic pressure enhancement and subsequently drove the storm main phase. It is found that both the magnetospheric compression that formed the storm initial phase and the storm main phase caused ionospheric scintillation. In comparison, the intensity of the ionospheric scintillation caused by the intense magnetospheric compression just before the storm main phase is even more pronounced. We also analyzed the impact of storms on standard point positioning (SPP), precise point positioning (PPP) and real-time kinematic (RTK) techniques. The positioning accuracies of single-frequency SPP and PPP experienced the most severe decline, and there was a noticeable increase in the initialization time for dual-frequency static PPP and RTK during the event. RTK demonstrated a shorter convergence time and higher accuracy during this event, but it was limited to short-baseline RTK (&amp;lt;30 km).

Statistical Investigation of the Storm Time Plasma Density Strip‐Like Bulges at Lower‐Mid Latitudes

AbstractThe strip‐like bulge is a storm‐time conjugate ionospheric plasma density enhancement, constituted by the plasmaspheric H+/He+, that extends widely (over 150° in longitude) in the zonal dimension but occupies only 1°–5° in latitude. Based on in‐situ measurements of 11 low earth orbit satellites, this study statistically investigates the bulge structures of geomagnetic storms driven by 136 interplanetary coronal mass ejections during 2000–2021. The statistical results show that the strip‐like bulges are observed at the end of the storm main phase and can persist for more than 60 hr. The spatial and temporal coverage of the strip‐like bulge varies from storm to storm. However, the bulges do exhibit occurrence preferences: stronger storms (for the ICME‐driven) during solar minimum periods, the Asian‐Pacific sector (with eastward magnetic declination), and the nightside of the dawn‐dusk terminator. A quiet time density enhancement called mid‐latitude enhancement could be recognized as a precursor of the strip‐like bulge. The evolution features of the plasmapause height exhibit similarities with the strip‐like bulge, indicating a field‐aligned downward and cross‐L inward intrusion of the plasmaspheric ions. The local net ion drifts partly support this scenario with downward/inward being the most dominant but not unique pattern, the other diverse net ion drift configurations exist but their impact on the strip‐like bulges remains unclear.

Nightside Detached Auroras Associated With Expanding Auroral Oval During the Main and Recovery Phases of a Magnetic Storm

AbstractDetached subauroral proton arcs are commonly observed during the recovery phase of geomagnetic storms, and have been extensively investigated. However, there is limited study on their occurrence during the main phase of storms. This study investigated nightside detached auroras (NDAs) observed by the far‐ultraviolet imager onboard the Defense Meteorological Satellite Program spacecraft. The NDAs occurred in the nightside sector, separated from the equatorward boundary of the auroral oval, and were observed during the main and recovery phases of the geomagnetic storm on 02 October 2013. The occurrence of the NDAs appears to correlate with the expanding auroral oval toward lower latitudes, and is independent of the polarity change in the interplanetary magnetic field Bz component. Particle measurements indicate that the NDAs were generated by energetic protons, primarily above 10 keV, originating from the ring current. These precipitating proton fluxes, predominantly anisotropic, were observed to be detached from the isotropic boundary within the auroral oval. Analysis of Pc1 data obtained by ground stations suggests that electromagnetic ion cyclotron waves account for the generation of the NDAs. The limited latitudinal distribution of the NDAs indicates the wave activity in the magnetospheric source region within a narrow L‐shell region. The observations presented in this study would contribute to our understanding of the coupling processes between the magnetosphere and ionosphere within the subauroral region.

Quantifying the Role of EMIC Wave Scattering During the 27 February 2014 Storm by RAM‐SCB Simulations

AbstractElectromagnetic Ion Cyclotron (EMIC) wave scattering has been proved to be responsible for the fast loss of both radiation belt (RB) electrons and ring current (RC) protons. However, its role in the concurrent dropout of these two co‐located populations remains to be quantified. In this work, we study the effect of EMIC wave scattering on both populations during the 27 February 2014 storm by employing the global physics‐based RAM‐SCB model. Throughout this storm event, MeV RB electrons and 100s keV RC protons experienced simultaneous dropout following the occurrence of intense EMIC waves. By implementing data‐driven initial and boundary conditions, we perform simulations for both populations through the interplay with EMIC waves and compare them against Van Allen Probes observations. The results indicate that by including EMIC wave scattering loss, especially by the He‐band EMIC waves, the model aligns closely with data for both populations. Additionally, we investigate the simulated pitch angle distributions (PADs) for both populations. Including EMIC wave scattering in our model predicts a 90° peaked PAD for electrons with stronger losses at lower pitch angles, while protons exhibit an isotropic PAD with enhanced losses at pitch angles above 40°. Furthermore, our model predicts considerable precipitation of both particle populations, predominantly confined to the afternoon to midnight sector (12 hr &lt; MLT &lt; 24 hr) during the storm's main phase, corresponding closely with the presence of EMIC waves.

Rapid Relativistic Electron Enhancements During Van Allen Probes Era

AbstractRelativistic electron fluxes in the outer radiation belt exhibit significant variability during geomagnetic storms and substorms. This study investigates rapid relativistic electron enhancements (REE) in the outer radiation belt throughout the entire Van Allen Probes (RBSP) era from October 2012 to October 2019. Utilizing RBSP measurements, we identify 182 rapid REE events characterized by a factor of greater than two increase in relativistic electron fluxes within a half RBSP orbit (approximately 4.5 hr) at L = 4.5–5.5. Approximately 76% of rapid REE events occur during geomagnetic storms. Rapid REEs during storms are concentrated within the 12‐hr period preceding and the 24‐hr period following the end of the storm's main phase. Intense REE are more likely found in storm's main phase compared to moderate REE. Sub‐relativistic and relativistic electron injections are commonly observed during rapid REE. Substorm activities (AL/AE, MPB index) and convection (AU index) are more intense before and during REE, in contrast to the intervals following REEs. The intensity of rapid REE correlates with the strength of substorms and convection. This comprehensive survey suggests that rapid REEs in the outer radiation belt are likely associated with, but not strictly tied to, geomagnetic storms. Enhanced convection and substorm appear to create favorable conditions for rapid REE. These substorms and enhanced convection are likely linked to favorable solar wind conditions for REEs, as documented in previous studies.

Regional Ionospheric Super Bubble Induced by Significant Upward Plasma Drift During the 1 December 2023 Geomagnetic Storm

AbstractAn unseasonal equatorial plasma bubble (EPB) event occurred in the East/Southeast Asian sector during the geomagnetic storm on 1 December 2023, causing strong amplitude scintillations from equatorial to middle latitudes. Based on the observations from multiple instruments over a large latitudinal and longitudinal region, the spatial features of the super EPB were investigated. The EPB developed vertically at a fast rising speed ∼470 m/s over the magnetic equator and extended to a very high middle latitude more than 40°N, despite that the storm intensity was not very strong with the minimum SYM‐H index −132 nT. In the zonal direction, the super EPB covered over a specific region ∼95–140°E, where the local sunset roughly coincided with southward turning of interplanetary magnetic field (IMF) Bz component. Before the onset of the super EPB, significant upward plasma drift up to ∼110 m/s was observed over the magnetic equator, which could amplify the growth rate of Rayleigh‐Taylor instability and lead to the generation of the super EPB. The significant drift was likely caused by eastward penetration electric field (PEF) due to sharp southward turning of IMF Bz. The local time of storm onset and duration of IMF Bz southward turning during the storm main phase may partly determine the onset region and zonal coverage of the EPB.

Responses of Field‐Aligned Currents and Equatorial Electrojet to Sudden Decrease of Solar Wind Dynamic Pressure During the March 2023 Geomagnetic Storm

AbstractWe present the observations of field‐aligned currents and the equatorial electrojet during the 23 March 2023 magnetic storm, focusing on the effect of the drastic decrease of the solar wind dynamic pressure occurred during the main phase. Our observations show that the negative pressure pulse had significant impact to the magnetosphere‐ionosphere system. It weakened large‐scale field‐aligned currents and paused the progression of the storm main phase for ∼3 hr. Due to the sudden decrease of the plasma convection after the negative pressure pulse, the low‐latitude ionosphere was over‐shielded and experienced a brief period of westward penetration electric field, which reversed the direction of the equatorial electrojet. The counter electrojet was observed both in space and on the ground. A transient, localized enhancement of downward field‐aligned current was observed near dawn, consistent with the mechanism for transmitting MHD disturbances from magnetosphere to the ionosphere after the negative pressure pulse.

Response to geomagnetic storm on 23–24 March 2023 long-lasting longitudinal variations of the global ionospheric TEC

This study examines the global behavior of the ionospheric TEC anomalies, i.e. their structures and temporal variability, during the initial, main and recovery phase of the geomagnetic storm occurring on 23–24 March 2023. For this purpose the global vertical TEC maps, generated by the NASA JPL IGS Ionosphere center, have been used and the geomagnetically forced anomalies have been presented in 2D (longitude-modip latitude) and polar maps. The main peculiar features of the TEC response could be summarized as: (i) the TOI-like event observed at the SH midnight hours during the main storm phase, and (ii) a clear longitude asymmetry between the TEC response at low and middle latitudes of the western and eastern hemispheres was seen; while the long-lasting positive response was evident for a full day in the western hemisphere the negative response or almost the lack of response was a characteristic of the eastern part. The study presented possible explanations of the above mentioned basic type of TEC anomalies by using the GUVY [O/N2] ratio maps and geomagnetic data from eight magnetometric stations situated at low latitudes for the separation of the effect generated by the DDEF. An attempt was made the observed TEC response during different storm phases to be reproduced. The presented reconstructions described in almost perfect way the real TEC responses and the RMSE assessments provided clear evidence for this evaluation.

Significant Midlatitude Bubble‐Like Ionospheric Super‐Depletion Structure (BLISS) and Dynamic Variation of Storm‐Enhanced Density Plume During the 23 April 2023 Geomagnetic Storm

AbstractThis paper investigates the midlatitude ionospheric disturbances over the American/Atlantic longitude sector during an intense geomagnetic storm on 23 April 2023. The study utilized a combination of ground‐based observations (Global Navigation Satellite System total electron content and ionosonde) along with measurements from multiple satellite missions (GOLD, Swarm, Defense Meteorological Satellite Program, and TIMED/GUVI) to analyze storm‐time electrodynamics and neutral dynamics. We found that the storm main phase was characterized by distinct midlatitude ionospheric density gradient structures as follows: (a) In the European‐Atlantic longitude sector, a significant midlatitude bubble‐like ionospheric super‐depletion structure (BLISS) was observed after sunset. This BLISS appeared as a low‐density channel extending poleward/westward and reached ∼40° geomagnetic latitude, corresponding to an APEX height of ∼5,000 km. (b) Coincident with the BLISS, a dynamic storm‐enhanced density plume rapidly formed and decayed at local afternoon in the North American sector, with the plume intensity being doubled and halved in just a few hours. (c) The simultaneous occurrence of these strong yet opposite midlatitude gradient structures could be mainly attributed to common key drivers of prompt penetration electric fields and subauroral polarization stream electric fields. This shed light on the important role of storm‐time electrodynamic processes in shaping global ionospheric disturbances.

Thermospheric Wind Response to March 2023 Storm: Largest Wind Ever Observed With a Fabry‐Perot Interferometer in Tromsø, Norway Since 2009

AbstractSolar cycles 24–25 were quiet until a geomagnetic storm with a Sym‐H index of −170 nT occurred in late March 2023. On March 23–24, a Fabry‐Perot interferometer (FPI; 630 nm) in Tromsø, Norway, recorded the highest thermospheric wind speed of over 500 m/s since 2009. Comparisons with magnetometer readings in Scandinavia showed that a large amount of electromagnetic energy was transferred to the ionosphere‐thermosphere system. Total electron content maps suggested an enlarged auroral oval and revealed that the FPI observed winds near the polar cap instead of inside the oval for a long period during the storm main phase. The FPI wind had a strong equatorward component during the storm, likely because of the powerful anti‐sunward ionospheric plasma flow in the polar cap. The positive Y‐component of the IMF for 6 days before the storm caused a successive westward component of the FPI‐measured wind during the storm main phase. On March 24, the first day of the storm recovery phase, thermospheric wind disturbed and the ionospheric density decreased significantly at high latitudes. This density depression lasted for several days, and a large amount of electromagnetic energy during the storm modified the thermospheric dynamics and ionospheric plasma density.

Multi-process driven unusually large equatorial perturbation electric fields during the April 2023 geomagnetic storm

The low latitude ionosphere and thermosphere are strongly disturbed during and shortly after geomagnetic storms. We use novel Jicamarca radar measurements, ACE satellite solar wind, and SuperMAG geomagnetic field observations to study the electrodynamic response of the equatorial ionosphere to the 23, 24 April 2023 geomagnetic storm. We also compare our data with results from previous experimental and modeling studies of equatorial storm-time electrodynamics. We show, for the first time, unusually large equatorial vertical and zonal plasma drift (zonal and meridional electric field) perturbations driven simultaneously by multi storm-time electric field mechanisms during both the storm main and recovery phases. These include daytime undershielding and overshielding prompt penetration electric fields driven by solar wind electric fields and dynamic pressure changes, substorms, as well as disturbance dynamo electric fields, which are not well reproduced by current empirical models. Our nighttime measurements, over an extended period of large and slowly decreasing southward IMF Bz, show very large, substorm-driven, vertical and zonal drift fluctuations superposed on large undershield driven upward and westward drifts up to about 01 LT, and the occurrence of equatorial spread F irregularities with very strong spatial and temporal structuring. These nighttime observations cannot be explained by present models of equatorial storm-time electrodynamics.

A storm-time global electron density reconstruction model in three-dimensions based on artificial neural networks

We present results of a dedicated global storm-time model for the reconstruction of ionospheric electron density in three-dimensions. Using the storm criterion of |Dst|⩾50 nT and Kp⩾4, the model is constructed using a combination of radio occultation and ionosonde data during the periods of 2006–2021 and 2000–2020, respectively. From the ionosonde data, only the bottomside electron density profiles up to the maximum height of the F2 layer (hmF2) are considered. In addition to the selection of storm-time data only for the model development, we have investigated the inclusion of time history for the geomagnetic storm indicator Kp at 9 and 33 h in an attempt to take into account the delay of physical processes related to atmospheric gravity waves or traveling ionospheric disturbances and thermospheric composition changes which drive varying ionospheric storm effects during storm conditions. Based on incoherent scatter radar data and in comparison with the IRI 2020 model, the developed storm-time model provides foF2 modelling improvement of above 50% during the storm main phase over Millstone Hill (42.6°N, 71.5°W) and Tromsø (69.6°N, 19.2°E) for the storm periods of 3–6 November 2021 and 23–25 March 2023, respectively. Modelled results for Jicamarca (11.8°S, 77.2°W) show that the storm-time model estimates foF2 by an improvement of over 20% during the main phase of the 07–10 September 2017 storm period. As the ionospheric conditions return to quiet time levels, the IRI 2020 model perform better than the constructed storm -time model

Investigation of Different ΣO/N2 Variations Observed by GOLD During a Minor Geomagnetic Storm From 2 to 4 August 2021

AbstractDuring a minor geomagnetic storm occurring from Aug 2 (day‐of‐year (DOY) 214) to Aug 4 (DOY 216), 2021, the National Aeronautics and Space Administration Global‐scale Observations of the Limb and Disk (GOLD) mission observed different column density ratio of O to N2 (ΣO/N2) variations in storm main and recovery phases. The percentage difference of ΣO/N2 between DOY 215 (disturbed day, main phase) and DOY 213 (quiet reference day) exhibits a depletion on the east side of the GOLD field‐of‐view (FOV). However, that of ΣO/N2 between DOY 216 (recovery phase) and 213 shows depletions on the west side of GOLD FOV. The National Center for Atmospheric Research Thermosphere Ionosphere Electrodynamics General Circulation Model qualitatively reproduced the observations. Analysis of the model output illustrates that the ΣO/N2 patterns in the two days are both formed due to the classical thermospheric composition theory and formed on DOY 214 and 215, respectively. Further investigation found that the ΣO/N2 depletion on DOY 214 and 215 both initially formed near 120–180°E, but the one on DOY 215 then quickly moved westward into the GOLD FOV, from local post‐midnight to pre‐midnight, near 19 UT. Then it moves equatorward and slowly westward. This results in the observed depletion structure on the west side of GOLD FOV. Model simulations show that the quick westward movement near 19 UT is due to the dominant positive Interplanetary Magnetic Field east‐west component (By) conditions.

The Relation Among the Ring Current, Subauroral Polarization Stream, and the Geospace Plume: MAGE Simulation of the 31 March 2001 Super Storm

AbstractThe geospace plume, referring to the combined processes of the plasmaspheric and the ionospheric storm‐enhanced density (SED)/total electron content (TEC) plumes, is one of the unique features of geomagnetic storms. The apparent spatial overlap and joint temporal evolution between the plasmaspheric plume and the equatorial mapping of the SED/TEC plume indicate strong magnetospheric‐ionospheric coupling. However, a systematic modeling study of the factors contributing to geospace plume development has not yet been performed due to the lack of a sufficiently comprehensive model including all the relevant physical processes. In this paper, we present a numerical simulation of the geospace plume in the 31 March 2001 storm using the Multiscale Atmosphere‐Geospace Environment model. The simulation reproduces the observed linkage of the two plumes, which, we interpret as a result of both being driven by the electric field that maps between the magnetosphere and the ionosphere. The model predicts two velocity channels of sunward plasma drift at different latitudes in the dusk sector during the storm main phase, which are identified as the sub‐auroral polarization stream (subauroral polarization streams (SAPS)) and the convection return flow, respectively. The SAPS is responsible for the erosion of the plasmasphere plume and contributes to the ionospheric TEC depletion in the midlatitude trough region. We further find the spatial distributions of the magnetospheric ring current ions and electrons, determined by a delicate balance of the energy‐dependent gradient/curvature drifts and the E × B drifts, are crucial to sustain the SAPS electric field that shapes the geospace plume throughout the storm main phase.

Occurrence of Large Geomagnetically Induced Currents Within the EPRI SUNBURST Monitoring Network

AbstractSpace weather, a natural hazard, can adversely impact human technological assets. High‐voltage electric power transmission grids constitute one of the most critical technological systems vulnerable to space weather driven geomagnetically induced currents (GICs). One of the major challenges pertaining to the study of GICs over the continental United States has been the availability of GIC measurements, which are critical for validation of geoelectric field and power flow models, for example. In this study, we analyze GIC measurements collected at 17 Electrical Power Research Institute (EPRI) SUNBURST transformer locations across the United States for which a GIC value of 10 A or greater was recorded. This data set includes 52 individual geomagnetic storms with Kp index 6 and above during the period from 2010 to 2021. The analysis confirms that there is a good correlation between the number of geomagnetic storms per year and the number of recorded GIC events. Our results also show that about 76% of the top 17 GIC events are associated with the storm main phase, while only 24% are attributed to storm sudden commencements. In addition, it is shown, for the first time, that mid‐latitude positive bays can cause large GICs over the continental United States. Finally, this study shows that the largest measured GIC event in the data set was associated with a localized intense dB/dt structure, which could be attributed to substorm activity.

The Distribution and Evolution of Storm Time Pc3‐5 ULF Wave Power Based on Satellite and Ground Observations

AbstractThe geomagnetic storm is an intense geomagnetic activity, and one important research aspect is the storm time ultralow frequency (ULF) waves, which can resonate with injected particles and impact particle dynamics in the inner magnetosphere. This study focuses on analyzing ULF wave power during geomagnetic storms on the ground, in the magnetosphere and in the solar wind. During the Van Allen Probe era from year 2012–2019, we identified 94 geomagnetic storm events with 25 as strong storms and 69 as moderate storms based on the variation of SYM‐H index. The analysis revealed that for both satellite and ground‐based measurements during storms with different intensity, the ULF wave power was dramatically enhanced in the main phase. In addition, the ULF wave power of strong storms was significantly stronger than that of moderate storms within the magnetosphere and on the ground. While the finding is opposite in the solar wind. Furthermore, the ULF wave power of strong storms exhibited a higher intensity at higher L shell values and in some cases, it can last up to ∼2 days. Besides, the ULF wave power displayed a linear correlation with the absolute value of the SYM‐H index during the storm main phase while it exhibited an exponential association with the absolute value of the SYM‐H index during the recovery phase. This comprehensive analysis offers valuable insights into the evolution of ULF waves in the inner magnetosphere during geomagnetic storm events, shedding light on plasma waves and wave‐particle interactions in this region.