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In the present study we examine three substorm events, Events 1-3, focusing on the spatio-temporal development of auroral electrojets (AEJs) before auroral breakup. In Events 1 and 2, auroral breakup was preceded by the equatorward motion of an auroral form, and the ground magnetic field changed northward and southward in the west and east of the expected equatorward flow, respectively. Provided that these magnetic disturbances were caused by local ionospheric Hall currents, this feature suggests that the equatorward flow turned both eastward and westward as it reached the equatorward part of the auroral oval. The auroral breakup took place at the eastward-turning and westward-turning branches in Events 1 and 2, respectively, and after the auroral breakup, the westward AEJ enhanced only on the same side of the flow demarcation meridian. The zonal flow divergence is considered as an ionospheric manifestation of the braking of an earthward flow burst in the near-Earth plasma sheet and subsequent dawnward and duskward turning. Therefore, in Events 1 and 2, the auroral breakup presumably mapped to the dawnward and duskward flow branches, respectively. Moreover, for Event 3, we do not find any pre-onset auroral or magnetic features that can be associated with an equatorward flow. These findings suggest that the braking of a pre-onset earthward flow burst itself is not the direct cause of substorm onset, and therefore, the wedge current system that forms at substorm onset is distinct from the one that is considered to form as a consequence of the flow braking.

We comprehensively analyzed geomagnetic perturbations using ground magnetic records from over 400 stations spanning four solar cycles, from 1976 to 2023. We assess the perturbations in the three magnetic components separately. Our study covers low, middle, and high magnetic latitudes in the northern magnetic hemisphere, with the primary objective of quantifying extreme values and evaluating their variability on magnetic latitude, local time, and solar cycle phases "minimum, ascending, maximum, and declining." Our findings reveal spatial patterns to be less discernible as perturbations intensify, with distinct responses at middle and high latitudes. The extreme values, defined as percentiles 0 and 100, were observed to be localized and randomly distributed in local time, especially in the east magnetic component. Additionally, we observed dusk‐dawn asymmetries in the magnitude of perturbations related to the auroral electrojets, indicating complex interactions between the magnetosphere and ionosphere. Furthermore, the results reveal a preference for the most significant extreme values to occur in the declining phase of the solar cycle. These insights deepen our understanding of geomagnetic perturbations and their variability, contributing to space weather forecasting and mitigation strategies. Plain Language Summary: The study aims to investigate the occurrence of geomagnetic perturbations across different regions of the Earth by analyzing data from the SuperMAG collaboration. The network records changes in Earth's magnetic field, and the study endeavors to determine the extent to which these disturbances vary across different parts of the Earth. We focused on low, middle, and high latitudes in the northern hemisphere to comprehensively understand the perturbations during their intensification. The findings of the study suggest that the behavior of the perturbations varies significantly across different regions. We observed that magnetic perturbations in the auroral region intensify more in the morning compared to the evening, indicating the dynamic interplay between Earth's magnetic field and charged particles from space. Additionally, the study discovered that as the disturbances grew stronger, they did not follow the same patterns. Instead, the disruptions varied depending on the location on Earth. Moreover, the perturbations seem to intensify more during the declining solar phase. This knowledge is crucial in predicting space weather, especially in protecting satellites and power grids from the effects of space storms. Key Points: We utilized magnetic records from about 400 stations spanning four solar cycles between 1976 and 2023 across three magnetic componentsThe strongest perturbations were found in the north magnetic component associated with the dawnside westward auroral electrojetThe weakest and most significant extreme values of perturbations were observed during ascending and declining solar phases, respectively [ABSTRACT FROM AUTHOR]

During 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. Key Points: Superposed epoch analysis shows dynamic evolution of O+ ions during geomagnetic stormsSignificant enhancement of the O+‐to‐H+ number density ratio observed at radial distances less than 12 REScalar temperature for both species show the arrival of heated ions far from Earth throughout the analyzed period [ABSTRACT FROM AUTHOR]

A characteristic feature of the main phase of geomagnetic storms is the dawn‐dusk asymmetric depression of low‐ and mid‐latitude ground magnetic fields, with largest depression in the dusk sector. Recent work has shown, using data taken from hundreds of storms, that this dawn‐dusk asymmetry is strongly correlated with enhancements of the dawnside westward electrojet and this has been interpreted as a "dawnside current wedge" (DCW). Its ubiquity suggests it is an important aspect of stormtime magnetosphere‐ionosphere (MI) coupling. In this work we simulate a moderate geomagnetic storm to investigate the mechanisms that give rise to the formation of the DCW. Using synthetic SuperMAG indices we show that the model reproduces the observed phenomenology of the DCW, namely the correlation between asymmetry in the low‐latitude ground perturbation and the dawnside high‐latitude ground perturbation. We further show that these periods are characterized by the penetration of mesoscale bursty bulk flows (BBFs) into the dawnside inner magnetosphere. In the context of this event we find that the development of the asymmetric ring current, which inflates the dusk‐side magnetotail, leads to asymmetric reconnection and dawnward‐biased flow bursts. This results in an eastward expansion and multiscale enhancement of the dawnside electrojet. The electrojet enhancement extends across the dawn quadrant with localized enhancements associated with the wedgelet current systems of the penetrating BBFs. Finally, we connect this work with recent studies that have shown rapid, localized ground variability on the dawnside which can lead to hazardous geomagnetically induced currents. Plain Language Summary: During geomagnetic storms, electric currents in space can have a dramatic effect on the magnetic field on the ground, causing so‐called geomagnetic disturbances (GMDs). Storm‐time GMDs exhibit a lopsided asymmetry: dusk‐biased near the equator and dawn‐biased at high latitudes where aurora usually occur. This asymmetry has been interpreted as a giant wedge‐like current system, a dawnside current wedge (DCW). Using a high‐resolution supercomputer model, we successfully reproduced the DCW and showed that it occurred during a period of intense, localized flow bursts, akin to bubbles, on the nightside of near‐Earth space. The bubbles' buoyancy propels them from the nightside inwards toward dawn, driving intense currents into the Earth's atmosphere. Our simulations suggest that the causal agent of these dawnside bubbles is magnetic reconnection, typically symmetric but skewed dawnward due to asymmetry in the ring current, a crescent‐shaped population of energetic ions in space which intensifies during geomagnetic storms. Understanding the cause of stormtime GMD asymmetry is not only important to characterize how electric currents bind the magnetosphere and upper atmosphere, but also to mitigate space weather hazards, as intense GMDs can disrupt and damage power systems on Earth. Key Points: Global model reproduces correlation between ring current asymmetry and dawnside electrojet inferred from hundreds of geomagnetic stormsAnalysis of the model reveals a dawnside current wedge mediated by mesoscale flow bursts and driven by an asymmetric substorm‐like processModel reveals multiscale enhancement of dawnside electrojet with space weather implications due to rapid, localized ground variability [ABSTRACT FROM AUTHOR]

The dawn‐dusk asymmetry of magnetic depression is a characteristic feature of the storm main phase. Recently Ohtani (2021, https://doi.org/10.1029/2021JA029643) reported that its magnitude is correlated with the dawnside westward auroral electrojet (AEJ) intensity, and suggested that the dawnside AEJ intensification is a fundamental process of the stormtime magnetosphere‐ionosphere coupling. In this study we observationally address the cause of the dawnside AEJ intensification in terms of four scenarios. That is, the dawnside AEJ intensifies because (a) the external driving of global convection strengthens, (b) solar wind compression enhances energetic electron precipitation, and therefore, ionospheric conductance, through wave‐particle interaction, (c) the substorm current wedge forms in the dawn sector, and (d) energetic electrons injected by nightside substorms drift dawnward, and the subsequent precipitation enhances ionospheric conductance. We find an event that fits each scenario, and therefore, none of these scenarios can be precluded. However, the result of a superposed epoch analysis shows that some causes are more prevalent than others. More specifically, (a) although the enhancement of external driving may precondition the dawnside AEJ intensification, it is rarely the direct cause; (b) external compression probably explains only a small fraction of the events; (c) prior to the dawnside AEJ intensification, the westward AEJ tends to intensify in the midnight sector along with mid‐latitude positive bays, which suggests that the substorm injection of energetic electrons is the most prevalent cause. This last result may also be explained by the dawnside expansion of the substorm current wedge, which, however, is arguably far less common. Key Points: During storms the dawnside westward auroral electrojet (AEJ) often intensifies causing temporal (∼2 hr) large (>1,000 nT) ground H reductionsEnhancement of dawnside ionospheric conductance following substorm e‐injection is the most prevalent cause of such AEJ intensificationsConductance enhancement following solar wind compression explains a small fraction of the dawnside AEJ intensification events [ABSTRACT FROM AUTHOR]

The formation of auroral beads, wavy onset arcs, is often discussed in terms of substorm initiation. The present study addresses several aspects of their development and propagation by examining ground all‐sky images for representative events for each aspect. The results are summarized as follows: (a) the expansion and propagation of auroral beads do not depend on whether they form east or west of a preceding equatorward flow; (b) Auroral beads propagate either eastward or westward when the westward auroral electrojet intensifies apparently not preceded by the approach of an equatorward flow in neighboring sectors; (c) A nearby arc does not seem to be affected even if auroral beads form only a few tenths of degree apart in latitude; (d) two wavy arcs occasionally form next to each other and propagate in different directions; (e) the evolution of beading arcs is not always conjugate in two hemispheres. Results (a) and (b) suggest that meso‐ or large‐scale ionospheric convection as inferred from ground magnetic disturbances does not regulate the development and propagation of auroral beads. Results (c) and (d) imply that the development of auroral beads can be attributed to a small‐scale process, possibly a convection flow, at a latitudinal scale of a few tenths of degree or less. Such a small‐scale process may not be conjugate in two hemispheres, which potentially explains Result (e). These results do not necessarily mean that the cause of auroral beads is ionospheric, but suggest that the magnetosphere‐ionosphere coupling plays an important role in their development. Key Points: The propagation direction of auroral beads is not regulated by meso‐ or large‐scale convection as inferred from ground magnetic disturbancesSome events show an adjacent arc apparently unaffected by the bead formation, and other events show two beading arcs propagating oppositelyEvolution of auroral beads is not always conjugate between two hemispheres suggesting the contribution of an ionospheric or M‐I process [ABSTRACT FROM AUTHOR]

Embedded Region 1 and 2 field‐aligned currents (FACs), intense FAC layers of mesoscale latitudinal width near the interface between large‐scale Region 1 and Region 2 FACs, are related to dramatic phenomena in the ionosphere such as discrete arcs, inverted‐V precipitation, and dawnside auroral polarization streams. These relationships suggest that the embedded FACs are potentially important for understanding ionospheric heating and magnetosphere‐ionosphere (M‐I) coupling and instabilities. Previous case studies of embedded FACs have led to the speculation that they may result from enhanced M‐I convection during active times. To explore this idea further, we investigate statistically their occurrence rates under a variety of geomagnetic conditions with a large event list constructed from 17 years of Defense Meteorological Satellite Program observations. The identification procedure is fully automated and explicit. The statistical results indicate that embedded Region 1 and 2 FACs are common, and that they have a higher chance to occur when the level of geomagnetic activity is higher (given by various indices), supporting the idea that they result from enhanced M‐I convection. Plain Language Summary: Earth's magnetosphere is coupled to its ionosphere by electric currents of different scales flowing along magnetic fields. Sometimes a special type of medium‐scale currents may significantly impact the ionosphere. From this statistical study, we found that these medium‐scale currents appear frequently and more often when the magnetosphere and ionosphere are characterized by a higher level of activity. These findings provide important information on how these medium‐scale systems are generated. Key Points: We designed an automated, explicit selection algorithm to build a large database of embedded Region 1 and 2 currentsEmbedded Region 1 and 2 (ER1 and ER2) currents appear frequently and preferentially under geomagnetically active conditionsThe latitudinal widths of ER1 and ER2 currents increase with geomagnetic activity but not as much as those of R1 and R2 currents do [ABSTRACT FROM AUTHOR]

The effects of free radicals and hypotaurine on the development of bovine embryos produced by in vitro fertilization of in vitro-matured oocytes were examined. Embryos that developed to the 4- to 6-cell stage after in vitro fertilization were cultured without feeder cells in TCM199 medium supplemented with 1% calf serum (CS) under either 5% C[O.sub.2] in air or 5% [O.sub.2], 5% C[O.sub.2] and 90% [N.sub.2]. The percentages of blastocysts (including early, expanding, and hatched stages) that developed under 5% [O.sub.2] was higher (P < .01) than the percentage of those that developed under 20% [O.sub.2]. The respective percentages in 5% vs 20% [O.sub.2] concentration were as follows: blastocysts (d 8), 49% vs 17%; expanded blastocysts (d 8), 19% vs 6%; hatched blastocysts (d 10), 16% vs 0%. The development of embryos to blastocysts was suppressed (P < .05) when oxygen radicals were generated in culture medium by 2,2[inches]-azobis(2-amidinopropane) dihydrochloride (AAPH) under both 5% and 20% [O.sub.2]. The addition of hypotaurine permitted the development of embryos to blastocyst stage in medium with AAPH only under 5% [O.sub.2] (P < .05), but superoxide dismutase (SOD) did not permit the development of embryos to blastocysts. Alternatively, when embryos were cultured in medium without AAPH, the rates of development into blastocysts under 20% [O.sub.2] increased (P [less than] .05) by the addition of hypotaurine and SOD. However, under 5% [O.sub.2], the rates of blastocyst formation were not improved by addition of hypotaurine and SOD. Moreover, the cell numbers of blastocysts cultured in medium containing hypotaurine were greater (P < .01) than those of blastocysts cultured in medium without hypotaurine. It is concluded that hypotaurine may exert beneficial effects on in vitro development of bovine embryos under both 20% [O.sub.2] and 5% [O.sub.2] of gaseous conditions. Key Words: Bovine, Embryos, Oxygen Concentration, In Vitro Development, Hypotaurine

Dispersionless injections, involving sudden, simultaneous flux enhancements of energetic particles over some broad range of energy, are a characteristic signature of the particles that are experiencing a significant acceleration and/or rapid inward transport at the leading edge of injections. We have statistically analyzed data from Van Allen Probes (also known as Radiation Belt Storm Probes [RBSP]) to reveal where the proton (H+) and electron (e–) dispersionless injections occur preferentially inside geosynchronous orbit and how they develop depending on local magnetic field changes. By surveying measurements of RBSP during four tail seasons in 2012–2019, we have identified 171 dispersionless injection events. Most of the events, which are accompanied by local magnetic dipolarizations, occur in the dusk‐to‐midnight sector, regardless of particle species. Out of the selected 171 events, 75 events exhibit dispersionless injections of both H+ and e–, which occur within 2 min of each other. With only three exceptions, the both‐species injection events are further divided into two main subgroups: One is the H+ preceding e– events with a time offset of tens of seconds between H+ and e–, and the other the concurrent H+ and e– events without any time offset. Our superposed epoch results raise the intriguing possibility that the presence or absence of a pronounced negative dip in the local magnetic field ahead of the concurrent sharp dipolarization determines which of the two subgroups will occur. The difference between the two subgroups may be explained in terms of the dawn‐dusk asymmetry of localized diamagnetic perturbations ahead of a deeply penetrating dipolarization front. Key Points: Typical evolution of dispersionless injections inside geosynchronous orbit and related magnetic changes is derived from the 2012–2019 Radiation Belt Storm Probes measurementsMost of the dispersionless injections occur in the dusk‐to‐midnight sector and at >5 RE, regardless of speciesThe presence or absence of negative dip ahead of dipolarization likely determines a temporal offset between the proton and electron injection onsets [ABSTRACT FROM AUTHOR]

The expansion phase of auroral substorms is characterized by the formation of an auroral bulge, and it is generally considered that a single bulge forms following each substorm onset. However, we find that occasionally two auroral intensifications takes place close in time but apart in space leading to the formation of double auroral bulges, which later merge into one large bulge. We report three such events. In those events the westward auroral electrojet intensified in each auroral bulge, and geosynchronous magnetic field dipolarized in the same sector. It appears that two substorms took place simultaneously, and each substorm was accompanied by the formation of its own substorm current wedge system. This finding strongly suggests that the initiation of auroral substorms is a local process, and there is no global reference frame for their development. For example, ideas such as (i) the auroralbreakup takes place in the vicinity of the Harang reversal and (ii) the westward traveling surge maps to the interface between the plasma sheet and low‐latitude boundary layer, do not necessarily hold for every substorm. Even if those ideas may be suggestive of causal magnetospheric processes, the reference structures themselves are probably not essential. It is also found that despite the formation of two distinct auroral bulges, the overall magnetosphere‐ionosphere current system is represented by one globally coherent system, and we suggest that its structure is determined by the relative intensities and locations of the two substorm current wedges that correspond to the individual auroral bulges. Key Points: Occasionally more than one auroral substorm develops simultaneously at different magnetic local times leading to the formation of double auroral bulgesIt is suggested that the initiation of auroral substorms is a local process, and there is no global reference frame for their developmentEven with double auroral bulges, the overall magnetosphere‐ionosphere current system is represented by one globally coherent system [ABSTRACT FROM AUTHOR]