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Interplanetary (IP) shocks are perturbations observed in the solar wind. IP shocks correlate well with solar activity, being more numerous during times of high sunspot numbers. Earth‐bound IP shocks cause many space weather effects that are promptly observed in geospace and on the ground. Such effects can pose considerable threats to human assets in space and on the ground, including satellites in the upper atmosphere and power infrastructure. Thus, it is of great interest to the space weather community to (a) keep an accurate catalog of shocks observed near Earth, and (b) be able to forecast shock occurrence as a function of the solar cycle (SC). In this work, we use a supervised machine learning regression model to predict the number of shocks expected in SC25 using three previously published sunspot predictions for the same cycle. We predict shock counts to be around 275 ± 10, which is ∼47% higher than the shock occurrence in SC24 (187 ± 8), but still smaller than the shock occurrence in SC23 (343 ± 12). With the perspective of having more IP shocks on the horizon for SC25, we briefly discuss many opportunities in space weather research for the remainder years of SC25. The next decade or so will bring unprecedented opportunities for research and forecasting effects in the solar wind, magnetosphere, ionosphere, and on the ground. As a result, we predict SC25 will offer excellent opportunities for shock occurrences and data availability for conducting space weather research and forecasting. Plain Language Summary: Solar activity is quite correlated with sunspot numbers. Alternating periods between solar minima and minima, termed solar cycle, usually occur every ∼11 years. As a result, researchers often attempt to predict sunspot occurrences for the following solar cycle. Solar perturbations occur more frequently during periods of high solar activity, and Earth‐bound perturbations can disturb the Earth's magnetic field in geospace and on the ground, affecting satellites and power infrastructure. In this work, we use an artificial intelligence supervised model to predict the number of shock occurrences in the ongoing solar cycle (beginning December 2019) by training the model with observations of sunspots and solar perturbations in the previous two solar cycles (August 1996–December 2019). Then, sunspot number predictions for the ongoing solar cycle are applied to the model, and predictions for the solar perturbations are obtained. We find that the number of predicted solar perturbations is ∼50% higher than their occurrence number in the previous solar cycle (December 2008–December 2019). Finally, we discuss how this relatively higher number of predicted solar perturbations can impact space weather research given the unprecedented number of data sets available in geospace and on the ground in the upcoming years. Key Points: SSN and shock count data in SC23‐24 are used with SSN predictions for SC25 in a supervised regression model to estimate shock counts in SC25We predict SC25 (275) will have ∼48% more shocks in comparison to SC24 (187), but it will have fewer shocks in comparison to SC23 (343)SC25 will offer unprecedented opportunities for space weather research given the availability of many data sets from space to the ground [ABSTRACT FROM AUTHOR]

Utilizing magnetic field measurements made by the Iridium satellites and by ground magnetometers in North America we calculate the full ionospheric current system and investigate the substorm current wedge. The current estimates are independent of ionospheric conductance, and are based on estimates of the divergence‐free (DF) ionospheric current from ground magnetometers and curl‐free (CF) ionospheric currents from Iridium. The DF and CF currents are represented using spherical elementary current systems (SECS), derived using a new inversion scheme that ensures the current systems' spatial scales are consistent. We present 18 substorm events and find a typical substorm current wedge (SCW) in 12 events. Our investigation of these substorms shows that during substorm expansion, equivalent field‐aligned currents (EFACs) derived with ground magnetometers are a poor proxy of the actual FAC. We also find that the intensification of the westward electrojet can occur without an intensification of the FACs. We present theoretical investigations that show that the observed deviation between FACs estimated with satellite measurements and ground‐based EFACs are consistent with the presence of a strong local enhancement of the ionospheric conductance, similar to the substorm bulge. Such enhancements of the auroral conductance can also change the ionospheric closure of pre‐existing FACs such that the ground magnetic field, and in particular the westward electrojet, changes significantly. These results demonstrate that attributing intensification of the westward electrojet to SCW current closure can yield false understanding of the ionospheric and magnetospheric state. Plain Language Summary: With a new inversion scheme we resolve the full current based on ground and space magnetometers and spherical elementary current systems We introduce a new inversion scheme for spherical elementary current systems to resolve the full current using ground and space magnetometers. Key Points: With a new inversion scheme we resolve the full current based on ground and space magnetometers and spherical elementary current systemsDuring substorms and close to the onset the ground‐based equivalent field‐aligned current is a poor proxy for the field‐aligned currentThe intensification of the westward electrojet can be a false indication of the formation of the substorm current wedge [ABSTRACT FROM AUTHOR]

This paper presents a multi-parameter global statistical model of extreme horizontal geomagnetic field fluctuations (dBH/dt), which are a useful input to models assessing the risk of geomagnetically induced currents in ground infrastructure. Generalised Pareto (GP) distributions were fitted to 1-min measurements of |dBH/dt| from 125 magnetometers (with an average of 28 years of data per site) and return levels (RL) predicted for return periods (RP) between 5 and 500 years. Analytical functions characterise the profiles of maximum-likelihood GP model parameters and the derived RLs as a function of corrected geomagnetic latitude, λ. A sharp peak in both the GP shape parameter and the RLs is observed at |λ| = 53° in both hemispheres, indicating a sharp equatorward limit of the auroral electrojet region. RLs also increase strongly in the dayside region poleward of the polar cusp (|λ| > 75°) for RPs > 100 years. We describe how the GP model may be further refined by modelling the probability of occurrences of |dBH/dt| exceeding the 99.97th percentile as a function of month, magnetic local time, and the direction of the field fluctuation, dBH, and demonstrate that these patterns of occurrence align closely to known patterns of auroral substorm onsets, ULF Pc5 wave activity, and (storm) sudden commencement impacts. Changes in the occurrence probability profiles with the interplanetary magnetic field (IMF) orientation reveal further details of the nature of the ionospheric currents driving extreme |dBH/dt| fluctuations, such as the changing location of the polar cusp and seasonal variations explained by the Russell-McPherron effect.

Learning from successful applications of methods originating in statistical mechanics, complex systems science, or information theory in one scientific field (e.g., atmospheric physics or climatology) can provide important insights or conceptual ideas for other areas (e.g., space sciences) or even stimulate new research questions and approaches. For instance, quantification and attribution of dynamical complexity in output time series of nonlinear dynamical systems is a key challenge across scientific disciplines. Especially in the field of space physics, an early and accurate detection of characteristic dissimilarity between normal and abnormal states (e.g., pre-storm activity vs. magnetic storms) has the potential to vastly improve space weather diagnosis and, consequently, the mitigation of space weather hazards. This review provides a systematic overview on existing nonlinear dynamical systems-based methodologies along with key results of their previous applications in a space physics context, which particularly illustrates how complementary modern complex systems approaches have recently shaped our understanding of nonlinear magnetospheric variability. The rising number of corresponding studies demonstrates that the multiplicity of nonlinear time series analysis methods developed during the last decades offers great potentials for uncovering relevant yet complex processes interlinking different geospace subsystems, variables and spatiotemporal scales. [ABSTRACT FROM AUTHOR]

Inverse modeling has become one of the primary methods for studying ionospheric electrodynamics, especially when using magnetic field measurements from below the ionosphere. We present a method for quantifying the spatial resolution in an inverse model for non‐uniformly sampled spatial data. This method provides a tool for assessing if a model can resolve the physical phenomena of interest. We quantify the spatial resolution for the Spherical Elementary Current System basis functions to model the ionospheric dynamics. Our results apply to models with spatially confined model parameters, unlike spherical harmonics where the model parameters describe the amplitude of global surface functions. The method is demonstrated for the upcoming Electrojet Zeeman Imaging Explorer cubesat mission which will provide spatially distributed remote sensing measurements of the magnetic field in the mesosphere. We show that, including measurements from a single ground magnetometer can significantly improve the spatial resolution. However, the impact of including a ground magnetometer depends on the relative position of the station with respect to the mesospheric measurements. In addition, a method for reducing two regularization parameters to one is presented. Reducing the amount of regularization parameters simplifies the optimization problem and facilitates a fair comparison between the models with and without a ground magnetometer. Key Points: A method for quantifying spatial resolution in inverse problems is presentedWe show that adding a ground magnetometer to a reconstruction based on Electrojet Zeeman Imaging Explorer satellite measurements improves accuracy locally and globallyA method for reducing model complexity by combining regularization parameters is presented [ABSTRACT FROM AUTHOR]

The relationship between solar-wind conditions and substorm activity is modelled with an approach based on an echo state network. Substorms are a fundamental physical phenomenon in the magnetosphere–ionosphere system, but the deterministic prediction of substorm onset is very difficult because the physical processes that underlie substorm occurrences are complex. To model the relationship between substorm activity and solar-wind conditions, we treat substorm onset as a stochastic phenomenon and represent the stochastic occurrences of substorms with a non-stationary Poisson process. The occurrence rate of substorms is then described with an echo state network model. We apply this approach to two kinds of substorm onset proxies. One is a sequence of substorm onsets identified from auroral electrojet intensity, and the other is onset events identified from activity of Pi2 pulsations, which are irregular geomagnetic oscillations often associated with substorm onsets. We then analyse the response of substorm activity to solar-wind conditions by feeding synthetic solar-wind data into the echo state network. The results indicate that the effect of the solar-wind speed is important, especially for Pi2 substorms. A Pi2 pulsation can often occur even if the interplanetary magnetic field (IMF) is northward, while the activity of auroral electrojets is depressed during northward IMF conditions. We also observe spiky enhancements in the occurrence rate of substorms when the solar-wind density abruptly increases, which might suggest an external triggering due to a sudden impulse of solar-wind dynamic pressure. It seems that northward turning of the IMF also contributes to substorm occurrences, though the effect is likely to be minor. [ABSTRACT FROM AUTHOR]

In this paper, we provide statistical evidence that the level of solar wind‐magnetosphere‐ionosphere (SW‐M‐I) coupling is weaker under radial (Sun‐Earth component dominant) interplanetary magnetic field (IMF) conditions than non‐radial IMF conditions. This is performed by analyzing auroral electrojet activity (using SuperMAG auroral electrojet indices) in the sunlit and dark ionospheres for long‐duration (at least 4 hr) radial IMF events and comparing against the same for long‐duration azimuthal (dusk‐dawn component dominant) IMF events. We show that the north‐south IMF component (IMF Bz) plays a crucial role in controlling the level of auroral electrojet activity as a negative half‐wave rectifier even for both IMF orientation categories. However, it is found that the magnitudes of the auroral electrojet indices are generally lower for radial IMF than for azimuthal IMF under similar sets of solar wind (radial bulk velocity and number density) and IMF Bz conditions, regardless of whether these indices are derived in the sunlit or dark regions. Moreover, the efficiency of coupling functions is lower for radial IMF than for azimuthal IMF, implying that increased coupling strength due to the azimuthal IMF component alone cannot well explain weaker auroral electrojets during radial IMF periods. Lastly, the contribution of the radial IMF component itself to auroral electrojet activity is also lower compared to the azimuthal IMF component. Our results suggest that the level of SW‐M‐I coupling characterized by auroral electrojet activity can be modulated by the radial IMF component, although the effect of this component is weaker than the other two IMF components. Plain Language Summary: The ionospheric electric current that flows along the auroral oval, called the auroral electrojet, is one of the manifestations of solar wind energy transfer into the magnetosphere‐ionosphere system via magnetic reconnection processes between the interplanetary and terrestrial magnetic field lines. Previous studies mainly focused on the role of interplanetary magnetic field (IMF) orientation in the plane perpendicular to the Sun‐Earth line (approximately solar wind flow direction) in controlling auroral electrojet activity, based on the dayside magnetopause magnetic field topology viewed from the Sun. In this study, we turn our attention to auroral electrojet activity under radial (nearly parallel to the Sun‐Earth line) IMF conditions by statistically examining the SuperMAG auroral electrojet indices for radial IMF intervals and comparing them with those for non‐radial IMF intervals under similar sets of interplanetary conditions. Our statistical results reveal that both the auroral electrojet intensity and the coupling efficiency between interplanetary and auroral electrojet parameters are lower under radial IMF conditions than non‐radial IMF conditions. These findings indicate that the radial component of the IMF can modulate the level of solar wind‐magnetosphere‐ionosphere coupling, although its effect is weaker than the other IMF components. Key Points: Auroral electrojet intensity is typically lower for radial interplanetary magnetic field (IMF) than for azimuthal IMF under similar IMF Bz and solar wind conditionsIncreased coupling strength due to IMF By alone cannot well explain weaker auroral electrojets during radial IMF compared to azimuthal IMFThe level of solar wind‐magnetosphere‐ionosphere coupling can be modulated by the radial IMF component as well as the other two IMF components [ABSTRACT FROM AUTHOR]

Ground‐based indices, such as the Dst, ap, and AE, have been used for decades to describe the interplay of the terrestrial magnetosphere with the solar wind and provide quantifiable indications of the state of geomagnetic activity in general. These indices have been traditionally derived from ground‐based observations from magnetometer stations all around the Earth. In the last 7 years though, the highly successful satellite mission Swarm has provided the scientific community with an abundance of high quality magnetic measurements at Low Earth Orbit, which can be used to produce the space‐based counterparts of these indices, such the Swarm‐Dst, Swarm‐ap, and Swarm‐AE indices. In this work, we present the first results from this endeavor, with comparisons against traditionally used parameters. We postulate on the possible usefulness of these Swarm‐based products for a more accurate monitoring of the dynamics of the magnetosphere and thus, for providing a better diagnosis of space weather conditions. Plain Language Summary: Ground‐based geomagnetic activity indices have been used for decades to monitor the dynamics of the Earth's magnetosphere, and provide information on two major types of space weather phenomena, that is, magnetic storm and magnetospheric substorm occurrence and intensity. This study demonstrates how magnetic field data from a Low Earth Orbit satellite mission, like ESA's Swarm constellation, can be used to derive corresponding space‐based geomagnetic activity indices. Swarm is unraveling one of the most mysterious aspects of our planet: the magnetic field. The magnetic field and electric currents in and around our planet generate complex forces that have immeasurable impact on everyday life. The comparison of Swarm‐based with ground‐based indices shows a very good agreement, indicating that Swarm magnetic field data can be used to provide new satellite‐based global indices to monitor the level of geomagnetic activity. Given the fact that the official ground‐based index for the substorm activity is constructed by data from 12 ground stations solely in the northern hemisphere, it can be said that this index is predominantly northern, while the Swarm‐derived substorm activity index may be more representative of a global state, since it is based on measurements from both hemispheres. Key Points: New geomagnetic activity indices based on Swarm magnetic field data are computed similar to standard ground‐based indices of Dst, ap, and AESwarm‐derived indices show excellent correlations with both the traditional and SuperMAG‐derived indicesSwarm‐based AE index enable us to monitor substorm activity also at the southern hemisphere [ABSTRACT FROM AUTHOR]

Large changes of the magnetic field associated with magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5–10 min duration have been frequently observed within a few hours of midnight. This study compares the statistical location of nighttime MPEs with |dB/dt| ≥ 6 nT/s within the auroral current system observed during 2015 and 2017 at two stations, Cape Dorset and Kuujjuarapik, in Eastern Canada. Maps of the two dimensional nightside auroral current system were derived using the Spherical Elementary Current Systems (SECS) technique. Analyses were produced at each station for all events, and for premidnight and postmidnight subsets. We examine four MPE intervals in detail, two accompanied by auroral images, and show the varying associations between MPEs and overhead ionospheric current systems including electrojets and the field‐aligned like currents. We find 225 of 279 MPEs occurred within the westward electrojet and only 3 within the eastward electrojet. For the premidnight MPEs 100 of 230 events occurred within the Harang current system while many of the remainder occurred within either the downward region 1 current system or the upward region 2 current system. Many of the 49 postmidnight MPEs occurred in either the downward region 1 (11 events) or upward region 2 current system (27 events). These result suggest that the source of MPEs in the premidnight sector is somewhere between the inner to mid plasma sheet and the source for the MPEs in the postmidnight sector is somewhere between the inner magnetosphere and the inner plasma sheet. Key Points: Magnetic perturbation events most frequently occur within a westward electrojetPremidnight MPEs commonly occur within the Harang current system and Postmidnight MPEs commonly occur within the region 2 upward currentsMagnetic perturbation events with all sky image data display a sudden brightening and distortion of auroral arcs [ABSTRACT FROM AUTHOR]

Rapid changes of magnetic fields associated with nighttime magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5–10 min duration can induce geomagnetically induced currents (GICs) that can harm technological systems. Here we present superposed epoch analyses of large nighttime MPEs (|dB/dt| ≥ 6 nT/s) observed during 2015 and 2017 at five stations in Arctic Canada ranging from 64.7° to 75.2° in corrected geomagnetic latitude (MLAT) as functions of the interplanetary magnetic field (IMF), solar wind dynamic pressure, density, and velocity, and the SML, SMU, and SYM/H geomagnetic activity indices. Analyses were produced for premidnight and postmidnight events and for three ranges of time after the most recent substorm onset: (a) 0–30 min, (b) 30–60 min, and (c) >60 min. Of the solar wind and IMF parameters studied, only the IMF Bz component showed any consistent temporal variations prior to MPEs: a 1–2 h wide 1–3 nT negative minimum at all stations beginning ∼30–80 min before premidnight MPEs, and minima that were less consistent but often deeper before postmidnight MPEs. Median, 25th, and 75th percentile SuperMAG auroral indices SML (SMU) showed drops (rises) before pre‐ and post‐midnight type A MPEs, but most of the MPEs in categories B and C did not coincide with large‐scale peaks in ionospheric electrojets. Median SYM/H indices were flat near −30 nT for premidnight events and showed no consistent temporal association with any MPE events. More disturbed values of IMF Bz, Psw, Nsw, SML, SMU, and SYM/H appeared postmidnight than premidnight. Key Points: Superposed epoch analyses of 2 years of >6 nT/s magnetic perturbation events (MPEs) from 5 high latitude Arctic stations are presentedOf the solar wind and interplanetary magnetic field (IMF) parameters studied, only IMF Bz showed any consistent pattern: a drop and rise prior to MPE occurrenceMost of the MPEs that occurred more than 30 min after a substorm onset did not coincide with peaks in the westward electrojet [ABSTRACT FROM AUTHOR]

We advance the modeling capability of electron particle precipitation from the magnetosphere to the ionosphere through a new database and use of machine learning (ML) tools to gain utility from those data. We have compiled, curated, analyzed, and made available a new and more capable database of particle precipitation data that includes 51 satellite years of Defense Meteorological Satellite Program (DMSP) observations temporally aligned with solar wind and geomagnetic activity data. The new total electron energy flux particle precipitation nowcast model, a neural network called PrecipNet, takes advantage of increased expressive power afforded by ML approaches to appropriately utilize diverse information from the solar wind and geomagnetic activity and, importantly, their time histories. With a more capable representation of the organizing parameters and the target electron energy flux observations, PrecipNet achieves a >50% reduction in errors from a current state‐of‐the‐art model oval variation, assessment, tracking, intensity, and online nowcasting (OVATION Prime), better captures the dynamic changes of the auroral flux, and provides evidence that it can capably reconstruct mesoscale phenomena. We create and apply a new framework for space weather model evaluation that culminates previous guidance from across the solar‐terrestrial research community. The research approach and results are representative of the "new frontier" of space weather research at the intersection of traditional and data science‐driven discovery and provides a foundation for future efforts. Plain Language Summary: Space weather is the impact of solar energy on society and a key to understanding it is the way that regions of space between the Sun and the Earth's surface are connected. One of the most important and most challenging to model are the way that energy is carried into the upper atmosphere (100–1,000 km altitude). Particles moving along magnetic field lines "precipitate" into this region, carrying energy and momentum which drive space weather. We have produced a new model, using machine learning (ML), that better captures the dynamics of this precipitation from a large volume of data. Machine learning models, carefully evaluated, are capable of better representing nonlinear relationships than simpler approaches. We reveal our approach to using ML for space weather and provide a new framework to understand these models. Key Points: We utilize a data‐driven organization of input parameters to produce a new total electron energy flux nowcast model (see Figure 4)Extended input features and higher expressive power provided by machine learning (ML) approach yields more capable mesoscale and peak flux specification (see Figure 7) and an overall reduction in specification errors compared with the state‐of‐the‐art (see Table 1)A framework for evaluation of ML (and any model) in geospace is suggested, building on momentum in the community (see Section 6) [ABSTRACT FROM AUTHOR]

We calculate high latitude electrodynamic parameters using global maps of field‐aligned currents from the Active Magnetosphere and Planetary Response Experiment (AMPERE). The model is based on previous studies that relate field‐aligned currents to auroral Pedersen and Hall conductances measured by incoherent scatter radar. The field‐aligned currents and conductances are used to solve for the electric potential at high latitudes from which electric fields are computed. The electric fields are then used with the conductances to calculate horizontal ionospheric currents. We validate the results by simulating the SuperMAG magnetic indices for 30 geomagnetically active days. The correlation coefficients between derived and actual magnetic indices were 0.68, 0.76, and 0.84 for the SMU, SML, and SME indices, respectively. We show examples of times when the simulations differ markedly from the measured indices and attribute them to either small‐scale, substorm‐related current structures or the effects of neutral winds. Overall, the performance of the model demonstrates that with few exceptions, auroral electrodynamic parameters can be accurately deduced from the global field‐aligned current distribution provided by AMPERE. Key Points: Relations between field‐aligned currents and ionospheric conductances are used to model electrical properties at high latitudesThe spatial and temporal distribution of electric fields and currents can be calculated from maps of field‐aligned currentsThe currents derived from the model accurately replicate magnetic indices based on the SuperMAG global magnetometer network [ABSTRACT FROM AUTHOR]

We observationally address substorm-related ground magnetic disturbances in terms of the substorm current wedge (SCW) system. The study consists of three data analyses, which approach different aspects of this subject. First, by comparing nightside magnetic disturbances below and above the ionosphere, we confirm that substorm-related midlatitude magnetic disturbances around the edges of the SCW can be attributed to a remote current system (i.e., SCW) rather than to a local ionospheric current. Second, we statistically examine the magnetic local time (MLT) distributions of the correlation between midlatitude magnetic variations and the nightside westward auroral electrojet (AEJ). We confirm that nightside magnetic disturbances are consistent with the SCW, and find that correlated magnetic variations extend to the midday sector. Finally, we introduce midlatitude and high-latitude geomagnetic indices for each MLT quadrant, and find that their variations are often correlated with the nightside AEJ intensity. From the magnitude of the correlated variations it is inferred that midday magnetic disturbances at both midlatitudes and high latitudes are remote effects of the SCW. In the dawn-sector and dusk-sector auroral zone, in contrast, correlated magnetic disturbances can be attributed mostly to the global enhancement of AEJs, which suggests that the global region-1 system also changes in correlation with the nightside westward AEJ during substorms. These results consistently indicate that ground magnetic disturbances are correlated globally with the substorm westward AEJ. In contrast, the geomagnetic effect of midlatitude ionospheric currents must be relatively small not only on the night side but also on the day side. [ABSTRACT FROM AUTHOR]

Rapid changes of magnetic fields associated with nighttime magnetic perturbation events (MPEs) with amplitudes |ΔB| of hundreds of nT and 5-10 min duration can induce geomagnetically induced currents (GICs) that can harm technological systems. This study compares the occurrence and amplitude of nighttime MPEs with |dB/dt| ≥ 6 nT/s observed during 2015 and 2017 at five stations in Arctic Canada ranging from 64.7° to 75.2° in corrected geomagnetic latitude (MLAT) as functions of magnetic local time (MLT), the SME (SuperMAG version of AE) and SYM/H magnetic indices, and time delay after substorm onsets. Although most MPEs occurred within 30 min after a substorm onset, ~10% of those observed at the four lower latitude stations occurred over two hours after the most recent onset. A broad distribution in local time appeared at all five stations between 1700 and 0100 MLT, and a narrower distribution appeared at the lower latitude stations between 0200 and 0700 MLT. There was little or no correlation between MPE amplitude and the SYM/H index; most MPEs at all stations occurred for SYM/H values between -40 and 0 nT. SME index values for MPEs observed >1 h after the most recent substorm onset fell in the lower half of the range of SME values for events during substorms, and dipolarizations in synchronous orbit at GOES 13 during these events were weaker or more often nonexistent. These observations suggest that substorms are neither necessary nor sufficient to cause MPEs, and hence predictions of GICs cannot focus solely on substorms. [ABSTRACT FROM AUTHOR]

The goal of the present study is to observationally test the idea that the substorm current wedge (SCW) is an ensemble of wedgelets, mesoscale current systems that correspond to plasma sheet flow channels. According to this hypothesis, the SML index, SuperMAG equivalent to the AL index, represents a single particular wedgelet at a given time, whereas midlatitude positive bays are a sum of the remote effects of all wedgelets but with more weighting on ones closer in longitude. However, both event-based and statistical studies of isolated substorms show that (1) midlatitude N (northward) and E (eastward) ground magnetic variations are highly correlated with SML even far from midnight; (2) the correlation between midlatitude magnetic variations and SML are organized by the magnetic local time (MLT) of the peak westward electrojet intensity (as identified by SML), and their longitudinal structures are consistent with the conventional SCW model; and (3) eastward and westward midlatitude E variations observed at dusk and dawn, respectively, are well correlated. If the SCW is an ensemble of wedgelets, these results would imply that wedgelets with similar intensities are formed side by side throughout the SCW and evolve in parallel with each other, which is highly questionable from both physical and morphological points of view. Instead, it is suggested that the SCW is basically a globally coherent system. Although the SCW may evolve from a wedgelet formed at the onset of substorms, wedgelets are probably not a primary constituent of the SCW for most of the subsequent expansion phase. [ABSTRACT FROM AUTHOR]

We model lower band chorus observations from the DEMETER satellite using daily and hourly autoregressive‐moving average transfer function (ARMAX) equations. ARMAX models can account for serial autocorrelation between observations that are measured close together in time and can be used to predict a response variable based on its past behavior without the need for recent data. Unstable distributions of radiation belt source electrons (tens of keV) and the substorm activity (SMEd from the SuperMAG array) that is thought to inject these electrons were both statistically significant explanatory variables in a daily ARMAX model describing chorus. Predictions from this model correlated well with observations in a hold‐out test data set (validation correlation of 0.675). Source electron flux was most influential when observations came from the same day or the day before the chorus measurement, with effects decaying rapidly over time. Substorms were more influential when they occurred on previous days, presumably due to their injecting source electrons from the plasma sheet. A daily ARMAX model with interplanetary magnetic field (IMF)|B|, IMF Bz, and solar wind pressure as inputs instead of those given above was somewhat less predictive of chorus (r=0.611). An hourly ARMAX model with only solar wind and IMF inputs was even less successful, with a validation correlation of 0.502. Key Points: Empirically based autoregressive‐moving average transfer function models predict daily‐averaged lower band chorus power wellValidation correlation between chorus observations and predictions using source electron flux and substorm activity as inputs was 0.675Source electron flux showed an immediate influence on chorus, while substorms were influential over many days [ABSTRACT FROM AUTHOR]

Subauroral polarization streams (SAPS) prefer geomagnetically disturbed conditions and strongly correlate with geomagnetic indexes. However, the temporal evolution of SAPS and its relationship with dynamic and structured ring current and particle injection are still not well understood. In this study, we performed detailed analysis of temporal evolution of SAPS during a moderate storm on 18 May 2013 using conjugate observations of SAPS from the Van Allen Probes (VAP) and the Super Dual Auroral Radar Network (SuperDARN). The large‐scale SAPS (LS‐SAPS) formed during the main phase of this storm and decayed due to the northward turning of the interplanetary magnetic field. A mesoscale (approximately several hundreds of kilometers zonally) enhancement of SAPS was observed by SuperDARN at 0456 UT. In the conjugate magnetosphere, a large SAPS electric field (∼8 mV/m) pointing radially outward, a local magnetic field dip, and a dispersionless ion injection were observed simultaneously by VAP‐A at L shell = 3.5 and MLT = 20. The particle injection observed by VAP‐A is likely associated with the particle injection observed by the Geostationary Operational Environmental Satellite 15 near 20 MLT. Magnetic perturbations observed by the ground magnetometers and flow reversals observed by SuperDARN reveal that this mesoscale enhancement of SAPS developed near the Harang reversal and before the substorm onset. The observed complex signatures in both space and ground can be explained by a two‐loop current wedge generated by the perturbed plasma pressure gradient and the diamagnetic effect of the structured ring current following particle injection. Key Points: Mesoscale enhancement of SAPS was observed by VAP and SuperDARN on top of the existing large‐scale SAPSMesoscale enhancement is associated with energetic ion flux increase, energetic electron flux decrease, and local magnetic field dipMesoscale enhancement of SAPS and equatorward flow burst developed near the Harang reversal [ABSTRACT FROM AUTHOR]

Abstract: Relativistic electron flux at geosynchronous orbit depends on enhancement and loss processes driven by ultralow frequency (ULF) Pc5, chorus, and electromagnetic ion cyclotron (EMIC) waves, seed electron flux, magnetosphere compression, the “Dst effect,” and substorms, while solar wind inputs such as velocity, number density, and interplanetary magnetic field Bz drive these factors and thus correlate with flux. Distributed lag regression models show the time delay of highest influence of these factors on log10 high‐energy electron flux (0.7–7.8 MeV, Los Alamos National Laboratory satellites). Multiple regression with an autoregressive term (flux persistence) allows direct comparison of the magnitude of each effect while controlling other correlated parameters. Flux enhancements due to ULF Pc5 and chorus waves are of equal importance. The direct effect of substorms on high‐energy electron flux is strong, possibly due to injection of high‐energy electrons by the substorms themselves. Loss due to electromagnetic ion cyclotron waves is less influential. Southward Bz shows only moderate influence when correlated processes are accounted for. Adding covariate compression effects (pressure and interplanetary magnetic field magnitude) allows wave‐driven enhancements to be more clearly seen. Seed electrons (270 keV) are most influential at lower relativistic energies, showing that such a population must be available for acceleration. However, they are not accelerated directly to the highest energies. Source electrons (31.7 keV) show no direct influence when other factors are controlled. Their action appears to be indirect via the chorus waves they generate. Determination of specific effects of each parameter when studied in combination will be more helpful in furthering modeling work than studying them individually. [ABSTRACT FROM AUTHOR]

The question of whether an interplanetary (IP) fast-mode shock can trigger the substorm expansion is still not resolved. Some scientists believe that the substorm expansion can be triggered by a sudden compression of the magnetosphere if a substorm growth phase is in progress (e.g., the magnetosphere precondition hypothesis). Such a hypothesis has not been rigorously tested. Here we study 258 positive sudden impulse (SI +) events associated with interplanetary fast-mode shocks observed by the ACE spacecraft from 1998 to 2009. The westward auroral electrojet SML index, derived from the SuperMAG network geomagnetic field data, is used to check for negative magnetic bays. It is found that the probability of having a magnetic bay onset that follows a shock impact peaks (~27%) sharply and immediately (within 3 min) after the shock-induced SI +. This indicates that the majority of the shock events do not lead to magnetic bays. A superposed epoch analysis of the shock events associated with (Type-Y) and without (Type-N) negative bays indicates that the Type-Y events had stronger (~40%) solar wind driving than the Type-N ones. This result generally supports the magnetosphere precondition hypothesis. We also found that (1) Type-Y events are associated with even stronger (~56%) solar wind driving downstream of the shock than Type-N events and (2) there is a good correlation between the SML and the polar cap magnetic PC indices both upstream and downstream of the shock. It is suggested that sharp decreases in SML immediately after a shock impact are not associated with the substorm-driven DP-1 current system but with the convection-driven DP-2 current system. [ABSTRACT FROM AUTHOR]