Phase Of Storm Research Articles

Solar cycle phase and occurrence of intense geomagnetic storms

Solar cycles have an asymmetrical shape with a fast rise and a slow decline, which varies from cycle to cycle. This makes it difficult to study the solar cycle phase dependence of the occurrence of intense solar-terrestrial events such as intense geomagnetic storms. In the previous works, differences in the rise and fall time lengths of each solar cycle were not fully considered. We normalized the asymmetric shape of each solar cycle using the rise and fall time lengths and showed the solar cycle phase dependence of occurrence of the intense geomagnetic storms selected using the Dst index for solar cycles 19−24 and using the aa index for solar cycles 12−24. The previous works noted that the occurrence of geomagnetic disturbances shows double peaks before and after solar maximum. Our results showed that the occurrence of the intense geomagnetic storms selected using the Dst and aa indices does not always show clear double peaks and increased more in the earlier half of the fall time than in the other time periods. The Dst and aa indices have been used to select geomagnetic storms in the previous studies. We pointed out that the solar cycle phase dependence of occurrence of the geomagnetic storms selected using the aa index is slightly different from those selected using the Dst index. We showed the geomagnetic storm on 4 August 1972 as an extreme case, which showed difference between Dst and aa. We also showed that intense geomagnetic storms associated with eruptive flares from the active sunspot groups occurred around the solar minima of cycles 17, 19, 20, and 21.Graphical

The Evolution of Earth's Outer Radiation Belt Over Geomagnetic Storm Phase in Van Allen Probe Era

AbstractEarth's outer radiation belts are highly dynamic during geomagnetic storms. Using electron flux data from 226 keV to 2.6 MeV measured by the Van Allen Probes, we statistically analyzed the peak flux position and inner boundary position of the outer radiation belt across different storm phases: pre‐storm quiet time, main phase, early recovery phase, and later recovery phase. This analysis covered 196 geomagnetic storm events from October 2012 to September 2019. Our results indicate that: (a) During the pre‐storm, decreases with increasing energy. From the pre‐storm to the early recovery phase, shifts inward for energies below 1 MeV and outward for energies above 1 MeV. For all energies, converges to approximately L = 4.3–4.6 in the early recovery phase. (b) Below approximately 1 MeV, generally move inward from the main phase to the early recovery phase. Above 1 MeV, remains nearly unchanged across different storm phases. (c) The half‐width (−) of the outer belt decreases during the main phase for energies below 1 MeV and increases during the recovery phase for energies above 1.5 MeV. (d) In the early recovery phase, and at 593–742 keV show a moderate correlation with storm intensity (CC 0.7–0.8), while and at energies greater than 1.1 MeV exhibit low correlations (CC0.4) during each phase. These results confirm the complex, energy‐dependent morphology of the outer radiation belt throughout geomagnetic storm phases.

6423 The Storm in a Healthy 26-year-old Hispanic Female

Abstract Disclosure: P.M. Reyes-Torres: None. M. Hernandez-Hernandez: None. Uncontrolled hyperthyroidism can cause thyrotoxicosis and lead to end-organ dysfunction known as thyroid storm. The incidence is .20 and .76 per 100,000 persons per year, with an incidence of 4.8–5.6 per 100,000 hospitalized patients. Of those hospitalized with thyrotoxicosis in the U.S., thyroid storm is diagnosed in 16%. Most commonly affects females, middle-aged patients, and Caucasians. Can be precipitated by acute illnesses, surgery, or non-compliance with medications. Symptoms are characterized by fever, cardiac and gastrointestinal dysfunction, and altered mentation along with impaired thyroid function tests.A 26-year-old Hispanic female presented to our ER complaining of palpitations, general malaise, dysphagia, and fevers after attending a social event 3 days before. Physical examination revealed a fever of 101F, restless patient with pressured speech, and diffusely enlarged non-tender thyroid without discrete nodules. Labs were remarkable for WBC: 12 000, urinalysis, b-HCG, and CXR were all negative. Burch-Wartofsky Point Scale: 55 and biochemical tests (TSH: 0.005 ml/UL, free T4 >5 ng/dL, Total T3: 8.5 ng/mL, Total T4: 28.87 uG/DL, Thyroglobulin 34.81 ng/mL) for which diagnosis of thyroid storm was made. She was transferred to the ICU and treatment was initiated with fluids, Propranolol 60 mg PO q4hrs, PTU 250 mg PO q4hrs, and Hydrocortisone 300 mg IV as loading dose then 100mg IV q8hrs. TSI and TRAb were ordered. Thyroid US remarkable for bulky thyroid gland with heterogeneous, increased vascularity, no obvious cystic/solid lesions seen. Repeated tests showed a decreasing trend of free T4: 4.71 ng/dL and Total T3: 2.42ng/dL for which PTU was discontinued and Methimazole 15 mg PO BID was started. Five days after treatment started, the patient continued symptom-free and was discharged with Propranolol 60 mg PO q6hrs and Methimazole 15 mg PO BID. TSI and TRAb samples were obtained but results were pending before discharge. Follow-up was scheduled in 2 weeks with routine labs but the patient was lost to follow-up.This case highlights the importance of early recognition and treatment of thyroid storm in Hispanics, undiagnosed patients given the presenting nonspecific, life-threatening symptoms. We conclude that our patient's cause of thyrotoxicosis was an undiagnosed case of Graves Disease and the storm was most likely triggered by an upper viral respiratory tract infection. This case could potentially help physicians identify hyperthyroidism in an earlier phase, reducing incidence, mortality, and hospitalizations of thyroid storm since a variety of mimics make the diagnosis challenging. Furthermore, we could contribute to updated statistical knowledge regarding the risk of patients with thyrotoxicosis developing thyroid storm which despite advancements in technology, are currently lacking. Presentation: 6/1/2024

Effects of Storm‐Time Winds on Ionospheric Pre‐Midnight Equatorial Plasma Bubbles Over South America as Observed by ICON and GOLD

AbstractThis study uses satellite measurements of plasma densities and thermospheric winds to analyze the effects of the November 2021 geomagnetic storm on ionospheric pre‐midnight topside plasma bubbles over South America. Using observations from the Ionospheric Connection Explorer (ICON) and the Global‐scale Observations of the Limb and Disk (GOLD) satellites, we find that pre‐midnight topside plasma bubbles were inhibited over eastern South America during the recovery phase of the storm. This is particularly notable because of the otherwise high occurrence rate of plasma bubbles at these longitudes during this season. This inhibition coincided with the recovery phase of the geomagnetic storm, marked by a northward turning of the z‐component of the interplanetary magnetic field (IMFBz) and quiet‐time values of the SuperMAG Auroral Electrojet Index (SME). We observed a westward turning of the zonal wind before the bubble inhibition, so we conclude the inhibition of topside plasma bubbles is likely related to a westward disturbance dynamo electric field (DDEF) causing a downward drift and suppress the growth of the instability responsible for bubble development. Contrary to theoretical predictions, we do not observe notable changes to the meridional wind during the event. These results provide new insights into the ionosphere‐thermosphere system's response to geomagnetic storms and highlight the role of wind patterns in inhibiting ionospheric irregularities, contributing to better predictive models for these phenomena.

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.

Paleostorm redeposition and post-glacial coastal chronology in the eastern Baltic Sea, Latvia

The 494 km long Latvian coast consists of sandy sediments, which serve as an excellent proxy for past coastal events and environment. Our study explores these understudied sediments along the western coast of the Gulf of Riga and combines two sand quartz-wise methods: optically stimulated luminescence (OSL) dating and grain microtextures. We provide a new chronology and microsedimentary results to trace post-glacial storm events and discuss correlations within the Baltic Sea region and elsewhere in Europe. OSL ages reveal a wide time span between 10.38 ± 0.61 ka and 1.04 ± 0.05 ka BP, but their inconsistency in the profiles along with the onshore position of landforms and gravelly horizons argues for sediment relocation due to storm action. A first paleostorm phase is dated to between 7.6 ± 1.2 ka and 4.63 ± 0.27 ka, corresponding with a transgression of the Littorina Sea and the Holocene Thermal Maximum, and with a roughly estimated vertical sediment redeposition above 5 m similar with the recent storms in the region. Sedimentary record from microstudy supports intense storm activity, especially in sediments redeposited after 6.07 ± 0.51 ka, and it is seen through an increased number of cracked quartz grains, shiny grains and fresh surfaces combined with a limited number of V-shaped marks. Weaker storm action, recorded by a lower share of cracked grains in the sediments, occurred between 7.6 ± 1.2 ka and 6.07 ± 0.51 ka.A second storm phase occurred at 1.44 ± 0.21 ka, corresponding with the post-Littorina, again with a performance of a weaker storm. Apart from the palaeostorm records, the beach ridges developed between 5.16 ± 0.33 ka and 4.47 ± 0.31 ka along with drier conditions when aeolian deposition took place twice: at 4.63 ± 0.27 ka and 1.55 ± 0.10 ka.

Using Satellite Observations of Lightning and Precipitation to Diagnose the Behavior of Deep Convection in Tropical Cyclones Traversing the Midlatitudes

AbstractThis study uses a unique combination of geostationary and low‐Earth orbiting satellite‐based lightning and precipitation observations, respectively, to examine the evolution of deep convection during the tropical cyclone (TC) lifecycle. The study spans the 2018–2021 Atlantic Basin hurricane seasons and is unique as it provides the first known analysis of total lightning (intra‐cloud and cloud‐to‐ground) observed in TCs through their extratropical transition and post‐tropical cyclone (PTC) phases. We consider the TC lifecycle stage, geographic location (e.g., land, coast, and ocean), shear strength, and quadrant relative to the storm motion and environmental shear vectors. Total lightning maxima are found in the forward right quadrant relative to storm motion and downshear of the TC center, consistent with previous studies using mainly cloud‐to‐ground lightning. Increasing environmental shear focuses the lightning maxima to the downshear right quadrant with respect to the shear vector in tropical storm phases. Vertical profiles of radar reflectivity from the Global Precipitation Measurement mission show that super‐electrically active convective precipitation features (>75 flashes) within the PTC phase of TCs have deeper mixed phase depths and higher reflectivity at −10°C than other phases, indicating the presence of more intense convection. Differences in the net convective behavior observed throughout TC evolution manifest in both the TC‐scale frequency of lightning‐producing cells and the intensity variations amongst individual convective cells. The combination of continuous lightning observations and precipitation snapshots improves our understanding of convective‐scale processes in TCs, especially in PTC phases, as they traverse the tropics and mid‐latitudes.

East–West Difference in the Ionospheric Response During the Recovery Phase of May 2024 Super Geomagnetic Storm Over the East Asian

AbstractIn this study, we offer an extensive examination of the F‐region ionospheric disturbances during the May 2024 superstorm, focusing primarily on the middle‐low latitude regions of East Asia. Our analysis is grounded in a wealth of data sources including Total Electron Content (TEC), ionospheric parameters NmF2 and hmF2, Electron Density Profile (EDP) retrieved from Radio Occultation (RO) data, and ∑[O]/[N2] from the Global Ultraviolet Imager (GUVI), among others, complemented by model simulations. The observed negative ionospheric storm effect, characterized by a significant and long‐lasting reduction in electron density across the entire China, commenced immediately following the sudden storm commencement (SSC) on 10 May and continued through the main and early recovery phase of the storm on 11 May. On 11–12 May, positive ionospheric storm impacts were initially observed in a restricted geographical area from the post‐midnight to sunrise, first manifesting over the eastern regions of China and then shifting to the central regions. Subsequently, a pronounced negative storm effect persisted throughout the later stages of recovery phase. In contrast, the western regions of China experienced a positive storm effect on 12 May followed by a comparatively mild negative storm phase. This persistent extensive zonal gradient in electron density across the East Asian region resembles the scenarios depicted in prior superstorms attributed to the thermospheric circulation patterns. The disparity in the ionospheric response from east to west in this area is probably a common feature during superstorms, potentially resulting from an arch‐shaped structure of elevated ∑[O]/[N2].

Differences in Ionospheric O+ and H+ Outflow During Storms With and Without Sawtooth Oscillations

AbstractPrevious simulations have suggested that O+ outflow plays a role in driving the sawtooth oscillations. This study investigates the role of O+ by identifying the differences in ionospheric outflow between sawtooth and non‐sawtooth storms using 11 years of FAST/Time of flight Energy Angle Mass Spectrograph (TEAMS) ion composition data from 1996 through 2007 during storms driven by coronal mass ejections. We find that the storm's initial phase shows larger O+ outflow during non‐sawtooth storms, and the main and recovery phases revealed differences in the location of ionospheric outflow. On the pre‐midnight sector, a larger O+ outflow was observed during the main phase of sawtooth storms, while non‐sawtooth storms exhibited stronger O+ outflow during the recovery phase. On the dayside, the peak outflow shifts significantly toward dawn during sawtooth storms. This strong dawnside sector outflow during sawtooth storms warrants consideration.

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.

Interhemispheric Asymmetry in the Seasonal Ionospheric Outflow

AbstractA comprehensive statistical study is conducted on O+ and H+ outflows obtained from the TEAMS/FAST data during the 23rd solar cycle (1996–2007). The study investigates interhemispheric asymmetry in ionospheric outflows during local summer, winter, and equinox seasons. Data are classified into two distinct periods: the pre‐storm and geomagnetic storm phases. Numerous statistical asymmetries are identified. The findings indicate that the dayside cusp consistently demonstrates more outflow rates of O+ and H+ in the northern hemisphere than southern hemisphere during geomagnetic storms in all seasons as well as during the pre‐storm period in the summer season with the exception of H+ during summer storms. Conversely, the nightside O+ and H+ outflow rates are higher in the southern hemisphere during pre‐storm and storm periods in the summer season. Additionally, the dawnside and duskside outflow rates of O+ and H+ are predominantly stronger in the southern hemisphere.

Report on the effects of the May 2024 Mother's day geomagnetic storm observed from Chile

This study investigates the extreme geomagnetic storm of May 10–15, 2024, utilizing data from the SER ground-based station in Chile and the DSCOVR satellite. The methodology involves calculating the horizontal magnetic field (H), filtering geomagnetic data using a Butterworth filter, and conducting cross-correlation analysis between solar wind parameters and Pc5 pulsations. The storm, starting with a sudden storm commencement triggered by a coronal mass ejection around 18:00 UT on May 10, exhibited a main phase lasting about 8 h, followed by a recovery phase starting on May 11. The extreme storm exhibited abrupt fluctuations in the interplanetary magnetic field data and solar wind parameters, inducing a depression in the geomagnetic field H-component reaching ΔH ∼ −551 nT at the SER station. Throughout the storm, solar wind parameters such as density, speed, and temperature exhibited varied ranges, with significant changes observed in all storm phases. Notably, during the initial and main phases, cross-correlation analysis unveiled robust associations between Pc5 pulsations and solar wind parameters such as density and speed, with maximum R values reaching 0.98 for both phases.

Inner Radiation Belt Simulations During the Successive Geomagnetic Storm Event of February 2022

AbstractStarting from 29 January 2022, a series of solar eruptions triggered a moderate geomagnetic storm on 3 February 2022, followed subsequently by another. Despite the typically minimal impact of unintense storms on space technology, 38 out of the 49 Starlink satellites underwent orbital decay, re‐entering Earth's atmosphere. These satellite losses were attributed to enhanced atmospheric drag conditions. This study employs numerical simulations, utilizing our test particle simulation code, to investigate the dynamics of the inner radiation belt during the two magnetic storms. Our analysis reveals an increase in proton density and fluxes during the transition from the recovery phase of the first storm to the initial phase of the second, primarily driven by intense solar wind dynamic pressure. Additionally, we assess Single Event Upset (SEU) rates, which exhibit a 50% increase in comparison to initial quiet conditions.

Полярные сияния в периоды экстремальных геомагнитных бурь: особенности среднеширотного сияния 11 февраля 1958 г.

This paper discusses peculiarities of the great mid-latitude aurora that occurred during the extreme magnetic storm on February 11, 1958. This mid-latitude aurora had unusual optical and spectral characteristics, among which, first of all, were very high (10⁵–10⁸ R) intensities of atomic oxygen [OI] 630.0 nm emission and an unusually high ratio of the intensities of two forbidden lines of oxygen [OI] 630.0 nm and 557.7 nm (I₆₃₀/I₅₅₇.₇). In some points, this ratio was as high as 10³–10⁴. Analysis of I₆₃₀ dynamics during other extreme geomagnetic storms and associated geophysical conditions and physical processes in Earth’s ionosphere and magnetosphere allows us to assume that great mid-latitude auroras are formed during intense substorms in main phases of magnetic storms. In order to interpret the observed features of the February 11, 1958 mid-latitude aurora, we propose to examine the mechanism of level [OI] ¹D selective filling in which reactions of resonance recharge of oxygen ions O⁺(²D)+O (³P)→O⁺(⁴S)+O(³P, ¹D) and/or reactions of oxygen atom and molecule collisions with excited components of odd nitrogen can be implemented.

Variability of ionospheric ionization over Eurasia according to data from a high-latitude ionosonde chain during extreme magnetic storms in 2015

. We have examined longitudinal-temporal variations in ionospheric parameters over Eurasia by analyzing data from a chain of high-latitude ionosondes along a latitude circle ~70° N (geomagnetic latitudes 58°<Glat<65°) in the longitudinal sector 26–171° E during severe magnetic storms of solar cycle 24 in March and June 2015. To analyze the response of ionospheric ionization to geomagnetic disturbances, we have used ionosonde data on hourly average critical frequency foF2 of the ionospheric F2 layer. Strong differences were observed between common peculiarities of temporal variations in foF2 for the analyzed periods of magnetic storms, which are likely associated with the characteristic features of the seasonal and diurnal variations in the background high-latitude ionosphere of the given geographic region. During the main and early recovery phases of magnetic storms there were periods of blackouts of ionosonde radio signals. Differences in the character of the ionospheric response to geomagnetic disturbances have been noted. This is probably due to seasonal features of the probability of occurrence of the ionospheric storm positive or negative phase in different seasons of the year. The trends of increasing ionospheric ionization over the vast region of Eastern, Western Siberia and Europe after the end of the extreme magnetic storm in March 2015, according to measurements from the chain of high-latitude ionosondes, may be associated with the formation of an area of increased [O]/[N₂] ratio over this territory. Such an increase in ionospheric ionization exceeding the background level of foF2 values can be considered as a clear manifestation of the after-effect of magnetic storms.

Auroras during extreme geomagnetic storms: Some features of mid-latitude aurora on February 11, 1958

This paper discusses peculiarities of the great mid-latitude aurora that occurred during the extreme magnetic storm on February 11, 1958. This mid-latitude aurora had unusual optical and spectral characteristics, among which, first of all, were very high (10⁵–10⁸ R) intensities of atomic oxygen [OI] 630.0 nm emission and an unusually high ratio of the intensities of two forbidden lines of oxygen [OI] 630.0 nm and 557.7 nm (I₆₃₀/I₅₅₇.₇). In some points, this ratio was as high as 10³–10⁴. Analysis of I₆₃₀ dynamics during other extreme geomagnetic storms and associated geophysical conditions and physical processes in Earth’s ionosphere and magnetosphere allows us to assume that great mid-latitude auroras are formed during intense substorms in main phases of magnetic storms. In order to interpret the observed features of the February 11, 1958 mid-latitude aurora, we propose to examine the mechanism of level [OI] ¹D selective filling in which reactions of resonance recharge of oxygen ions O⁺(²D)+O (³P)→O⁺(⁴S)+O(³P, ¹D) and/or reactions of oxygen atom and molecule collisions with excited components of odd nitrogen can be implemented.

Изменчивость ионизации ионосферы над Евразией по данным цепи высокоширотных ионозондов во время экстремальных магнитных бурь 2015 г.

. We have examined longitudinal-temporal variations in ionospheric parameters over Eurasia by analyzing data from a chain of high-latitude ionosondes along a latitude circle ~70° N (geomagnetic latitudes 58°<Glat<65°) in the longitudinal sector 26–171° E during severe magnetic storms of solar cycle 24 in March and June 2015. To analyze the response of ionospheric ionization to geomagnetic disturbances, we have used ionosonde data on hourly average critical frequency foF2 of the ionospheric F2 layer. Strong differences were observed between common peculiarities of temporal variations in foF2 for the analyzed periods of magnetic storms, which are likely associated with the characteristic features of the seasonal and diurnal variations in the background high-latitude ionosphere of the given geographic region. During the main and early recovery phases of magnetic storms there were periods of blackouts of ionosonde radio signals. Differences in the character of the ionospheric response to geomagnetic disturbances have been noted. This is probably due to seasonal features of the probability of occurrence of the ionospheric storm positive or negative phase in different seasons of the year. The trends of increasing ionospheric ionization over the vast region of Eastern, Western Siberia and Europe after the end of the extreme magnetic storm in March 2015, according to measurements from the chain of high-latitude ionosondes, may be associated with the formation of an area of increased [O]/[N₂] ratio over this territory. Such an increase in ionospheric ionization exceeding the background level of foF2 values can be considered as a clear manifestation of the after-effect of magnetic storms.

The effect of continuous geomagnetic storms on enhancements of ultrarelativistic electrons in the Earth’s outer radiation belt

The effect of continuous geomagnetic storms on enhancements of ultrarelativistic electrons in the Earth’s outer radiation belt

Magnetospheric Time‐History in Storm‐Time Magnetic Flux Dynamics: A Global Simulation Campaign

AbstractThis paper aims to quantify the magnetospheric magnetic flux contents under moderate to intense space weather conditions using global simulations. This study is a companion to Akhavan‐Tafti, Atilaw, et al. (2023, https://doi.org/10.1029/2023JA031832) where magnetic flux evolution is presented for a catalog of storm events, using Heliophysics System Observatory (HSO) observations. For this study, we used the Space Weather Modeling Framework (SWMF) in Geospace configuration to study magnetic flux dynamics for a subset of their storm events (15 events). Simulations reliably resolve the storm‐time magnetic flux Bz and current density |J| asymmetries across the different storm phases. It is revealed that: relative to the quiet period, flux content is enhanced during the storm sudden commencement (SSC) phase in the dayside by ΔBz/Bz, quiet = +17%, and reduced in the nightside magnetosphere (r[RE] < −6 RE) by −15%. At the same time, the cross‐tail current is found to enhance (|J| = 2 nA/m2), which suggests the storm impact in the nightside magnetosphere is much earlier in the storm cycle than previously shown. Concurring with previous studies, a significant depletion of magnetic flux by up to −40%, with day‐night and dawn‐dusk asymmetries, can be seen during the main and recovery phases. This corresponds to the enhanced current density (|J| = 5–8 nA/m2) at ∼6 RE further confirming the role of ring current in driving magnetospheric dynamics during the main and recovery phases. This is in contrast with the SSC phase wherein the Chapman‐Ferraro and cross‐tail currents are the dominant current systems.

Temporal Evolution of O+ Population in the Near‐Earth Plasma Sheet During Geomagnetic Storms as Observed by the Magnetospheric Multiscale Mission

AbstractDuring geomagnetic storms, the increase in energy input into the ionosphere in the form of Poynting flux and electron precipitation leads to an enhanced ionospheric outflow that results in an increase of the O+ content in the magnetosphere. Using different missions and instrumentation, two main ionospheric sources have been identified for the oxygen ions reaching the inner magnetosphere during geomagnetic storms: the dayside cusp, and the night side auroral region. Evidence of both pathways have been presented in the literature. However, the relative contribution of each of these pathways to the enhancement of O+ observed in near‐Earth plasma sheet, as well as the dynamics involved during the development of geomagnetic storms remains an open question. Here, we present the first statistical study to date to address this question, in the form of a superposed epoch analysis of O+ and H+ moments obtained by the Magnetospheric Multiscale (MMS) mission throughout the main phase of 90 geomagnetic storms with a minimum SYM‐H of at least −50 nT. The results show a clear increase in the oxygen density in the near‐Earth plasma sheet, with values further from Earth remaining low. Temperature values for both species show an increase with the progress of the storms. These results combined suggest that, during the main phase of geomagnetic storms, most of the oxygen ions observed in the near‐Earth plasma sheet are traveling directly from the nightside auroral region.