One of the most prominent (and potentially dangerous) features of space weather are geomagnetically induced currents, commonly known as GICs. The understanding of GICs is a major concern in order to preserve the power and communication systems and other technology on the ground. GICs are currents induced by rapid fluctuations in the Earth's magnetic field in any extended conducting technological infrastructure and can lead to malfunction or black outs of high-voltage power transmission systems (

We present a case study of eight successive plasma sheet (PS) activations (usually referred to as bursty bulk flows or dipolarization fronts), associated with small individual BZGSM increases on 31 March 2009 (0200–0900 UT), observed by the Time History of Events and Macroscale Interactions During Substorms mission. This series of events happens during very quiet solar wind conditions, over a period of 7 h preceding a substorm onset at 1230 UT. The amplitude of the dipolarizations increases with time. The low‐amplitude dipolarization fronts are associated with few (1 or 2) rapid flux transport events (RFT, Eh>2 mV/m), whereas the large‐amplitude ones encompass many more RFT events. All PS activations are associated with small and localized substorm current wedge (SCW)‐like current system signatures, which seems to be the consequence of RFT arrival in the near tail. The associated ground magnetic perturbations affect a larger part of the contracted auroral oval when, in the magnetotail, more RFT are embedded in PS activations (>5). Dipolarization fronts with very low amplitude, a type usually not included in statistical studies, are of particular interest because we found even those to be associated with clear small SCW‐like current system and particle injections at geosynchronous orbit. This exceptional data set highlights the role of flow bursts in the magnetotail and leads to the conclusion that we may be observing the smallest form of a substorm or rather its smallest element. This study also highlights the gradual evolution of the ionospheric current disturbance as the plasma sheet is observed to heat up.

The response of the Earth's magnetosphere to changing solar wind conditions is studied with a 3-D Magnetohydrodynamic (MHD) model. One full year (155 Cluster orbits) of the Earth's magnetosphere is simulated using Grand Unified Magnetosphere Ionosphere Coupling simulation (GUMICS-4) magnetohydrodynamic code. Real solar wind measurements are given to the code as input to create the longest lasting global magnetohydrodynamics simulation to date. The applicability of the results of the simulation depends critically on the input parameters used in the model. Therefore, the validity and the variance of the OMNIWeb data are first investigated thoroughly using Cluster measurement close to the bow shock. The OMNIWeb and the Cluster data were found to correlate very well before the bow shock. The solar wind magnetic field and plasma parameters are not changed significantly from the L 1 Lagrange point to the foreshock; therefore, the OMNIWeb data are appropriate input to the GUMICS-4. The Cluster SC3 footprints are determined by magnetic field mapping from the simulation results and the Tsyganenko (T96) model in order to compare two methods. The determined footprints are in rather good agreement with the T96. However, it was found that the footprints agree better in the Northern Hemisphere than the Southern one during quiet conditions. If the B y is not zero, the agreement of the GUMICS-4 and T96 footprint is worse in longitude in the Southern Hemisphere. Overall, the study implies that a 3-D MHD model can increase our insight of the response of the magnetosphere to solar wind conditions.

[1] Comparisons of multispacecraft observations and full-particle simulations are used to understand magnetotail changes during substorms and the related cross-tail current disruptions/reductions. We first show that the electric field accompanying current disruptions can be measured in the tail lobe from the drift velocity of oxygen beams. A stormy period is studied here with a fleet of spacecraft including the four Cluster spacecraft and the Double Star spacecraft TC-1 in the tail, ACE and Geotail respectively in the solar wind and magnetosheath, and five LANL geostationary satellites, thus allowing the determination of the direction of propagation of the substorm disturbances. Each substorm here corresponds to an energy-loading period followed by a dipolarization of the magnetic field seen from 11 to 18 R E . Plasma sheet thinning inside 12 R E occurs during energy loading and is enhanced at the onset of strong dissipations of magnetic energy, which precede by several minutes particle injections at 6.6 R E . Dipolarizations coincide with an increase of the lobe electric field, up to several mV/m. This study shows that the onset of the magnetic energy conversion occurs at about $10-11 R E and that once initiated, the perturbation propagates both toward the Earth and toward the distant tail. Comparisons of the measurements with recently published 2D full particle simulations of the reconnection process by Oka et al. (2008) indicate a good agreement between data and simulated magnetic lobe signatures. This suggests that the lobe magnetic changes are the signature of a tailward retreating neutral line, with its associated current disruption/reduction. Citation: Sauvaud, J. -A., et al. (2012), A study of the changes of the near-Earth plasma sheet and lobe driven by multiple substorms: Comparison with a full particle simulation of reconnection,

[1] The THEMIS mission includes three closely separated probes that provide the opportunity to analyze the small and meso-scale dynamics of the cross-tail current sheet in the near-Earth magnetosphere (10 Re). In this study, we focus on dipolarization events which occurred when two of these satellites were: (1) separated only along the Z direction (i.e., at the same location in the XY GSM ) plane, and: (2) on separate sides of the neutral sheet. Following these criteria, our search resulted in 25 dipolarization events. Most of them were not associated with global auroral substorm but were rather associated with arc intensification and magnetic perturbation observed from the ground only in limited local time sectors. Based on these, we demonstrate that dipolarizations systematically correspond to a thickening of the current sheet rather than any other phenomena (e.g., flapping). We also show that the current density in the sheet systematically decreases after onset. Most of the events show an increase of the Laplace force and of the magnetic tension after the dipolarization onset. This trend is however, sensitive to the coordinate system chosen (i.e., GSM or SM). We find that the total energy density (total pressure) increases after 70% of the dipolarization events. However, when excluding the Z-component of the magnetic field (which is canceled by the dominant curvature terms) from the pressure, we find that the pressure decreases after 64% of events, and the remaining pressure increases occur closest to the neutral sheet. Five minutes averages are used 5 to 10 min before dipolarization and 10 to 15 min after dipolarization. We discuss the importance of both the spacecraft location relative to the neutral sheet and timescales chosen when calculating the pressure changes. These directly impact interpretations relative to dipolarization models.