model revealed systematic discrepancies between the observed and predicted amplitudes, which suggested us to include additional region 2 sense currents (R2 loop) earthward of the dipolarized region (SCW2L model). Here we discuss alternative circuit geometries of the 3-D substorm current system and interpret observations of the magnetic field dipolarizations made between 6.6 R E and 11 R E , to quantitatively investigate the SCW2L model parameters. During two cases of a dipole-like magnetotail configuration, the dipolarization/injection front fortuitously stopped at r ∼ 9 R E for the entire duration of ∼ 30 min long SCW-related dipolarization within a unique, radially distributed multispacecraft constellation, which allowed us to determine the locations and total currents of both SCW2L loops. In addition, we analyzed the dipolarization amplitudes in events, simultaneously observed at 6.6 R E , 11 R E and at colatitudes under a wide range of magnetograph conditions. We infer that the ratio I 2 ∕I 1 varies in the range 0.2 to 0.6 (median value 0.4) and that the equatorial part of the R2 current loop stays at r > 6.6 R E in the case of a dipole-like field geometry (BZ 0 > 75 nT at 6.6 R E prior to the onset), but it is located at r < 6.6 R E in the case of a stretched magnetic field configuration (with BZ 0 < 60 nT). Since the ground midlatitude perturbations are sensitive to the combined effect of the R1 and R2 sense current loops with the net current roughly equal to I 1 − I 2 , the ratio I 2 /I 1 becomes an important issue when attempting to monitor the current disruption intensity from ground observations.

[1] Although the substorm current wedge (SCW) is recognized as a basic 3-D current system of the substorm expansion phase, its existing models still do not extend beyond a cartoon-like sketch, and very little is known of how well they reproduce magnetic variations observed in the magnetosphere during substorms. A lack of a realistic quantitative SCW model hampers testing model predictions against large sets of spacecraft data. This paper (1) presents a computationally efficient and flexible model with a realistic geometry of field-aligned currents, conveniently parameterized by the SCW strength, longitudinal width, and position, all derived from ground-based midlatitude magnetic variations; and (2) tests the model against INTERMAGNET network observations during substorms and compares its predictions with space magnetometer data. The testing demonstrated significant and systematic discrepancies between the observed and predicted magnetic variations, depending on spacecraft location, concurrent magnetotail configuration, and substorm phase. In particular, we found that the net SCW current derived from the midlatitude field variations corresponds to only a relatively small and variable fraction of the distant 3-D substorm current, inferred from spacecraft data in the lobe and at geosynchronous distance. The discrepancy can be partly attributed to additional region 2 polarity field-aligned currents in the same longitudinal sector, associated with azimuthal diversion of the earthward plasma flow when it encounters the region of strong quasi-dipolar field in the inner magnetosphere.

Key Points:• Azimuthal SCW dynamics nicely order various substorm signatures in the tail • AMPERE confirms quadrupolar FAC source of SCW supporting two-loop model • SCW2L model outperforms other models in describing dipolarized configuration Supporting Information:• Readme • Animation S1• Animation S2• Figure S1 • Figure S2 • Figure S3 Correspondence to: Abstract Unprecedented spacecraft and instrumental coverage and the isolated nature and distinct step-like development of a substorm on 17 March 2010 has allowed validation of the two-loop substorm current wedge model (SCW2L). We find a close spatiotemporal relationship of the SCW with many other essential signatures of substorm activity in the magnetotail and demonstrate its azimuthally localized structure and stepwise expansion in the magnetotail. We confirm that ground SCW diagnostics makes it possible to reconstruct and organize the azimuthal spatiotemporal substorm development pattern with accuracy better than 1 h magnetic local time (MLT) in the case of medium-scale substorm. The Active Magnetosphere and Planetary Electrodynamics Response Experiment (AMPERE)-based study of global field-aligned current distribution indicates that (a) the SCW-related field-aligned current system consists of simultaneously activated R1-and R2-type currents, (b) their net currents have a R1-sense, and (c) locations of net current peaks are consistent with the SCW edge locations inferred from midlatitude variations. Thanks to good azimuthal coverage of four GOES and three Time History of Events and Macroscale Interactions during Substorms spacecraft, we evaluated the intensities of the SCW R1-and R2-like current loops (using the SCW2L model) obtained from combined magnetospheric and ground midlatitude magnetic observations and found the net currents consistent (within a factor of 2) with the AMPERE-based estimate. We also ran an adaptive magnetospheric model and show that SCW2L model outperforms it in predicting the magnetic configuration changes during substorm dipolarizations.

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In this paper we study the properties of QCD at nonzero chiral density ρ5, which is introduced through chiral chemical potential µ5. The study is performed within lattice simulation of QCD with dynamical rooted staggered fermions. We first check that ρ5 is generated at nonzero µ5 and in the chiral limit observe ρ5 ∼ Λ 2 QCD µ5. We also test the possible connection between confinement and topological fluctuations. To this end, we measured the topological susceptibility χ top and string tension σ for various values of µ5. We observed that both string tension and chiral susceptibility grow with µ5 and there is a strong correlation between these quantities. We thus conclude that the chiral chemical potential enhances topological fluctuations and that these fluctuations can indeed be closely related to the strength of confinement.