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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, theSMLindex, SuperMAG equivalent to theALindex, 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) midlatitudeN(northward) andE(eastward) ground magnetic variations are highly correlated withSMLeven far from midnight; (2) the correlation between midlatitude magnetic variations andSMLare organized by the magnetic local time (MLT) of the peak westward electrojet intensity (as identified bySML), and their longitudinal structures are consistent with the conventional SCW model; and (3) eastward and westward midlatitudeEvariations 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.

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.

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.

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.

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|, IMFB_z, 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.

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.

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 atLshell = 3.5 andMLT = 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.