Spatial Structure and Asymmetries of Magnetospheric Currents Inferred from High‐Resolution Empirical Geomagnetic Field Models

Sitnov, M. I.; Stephens, G. K.; Tsyganenko, N. A.; Ukhorskiy, A. Y.; Wing, Simon; Korth, H.; Anderson, B. J.

doi:10.1002/9781119216346.ch15

Cited by 15 publications

(32 citation statements)

References 66 publications

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“…Later, the increase in the size of the model's database and the number of degrees of freedom for equatorial currents allowed us to resolve more details of the storm‐time current systems, including the eastward current and its closure paths with the main (westward) partial ring current forming a horse‐shoe‐like current structure (Stephens et al, ), as well as storm‐time distributions of the plasma pressure (Sitnov et al, ). Similar improvement of the field‐aligned current (FAC) system (Sitnov et al, ) revealed the spiral structure of the low‐altitude FAC distributions, which can be independently reconstructed using LEO spacecraft observations (Iijima & Potemra, ).…”

Section: Methodsmentioning

confidence: 86%

“…SST19 also includes a flexible FAC system (Sitnov et al, ), necessary to reproduce the spiral FAC structure at low latitudes. Its importance was found in the first substorm reconstructions (Stephens et al, ), and it is likely explained by the important role played by the Harang reversal region (Harang, ) in the substorm reconfigurations of the magnetosphere (Zou et al, ).…”

Section: Methodsmentioning

confidence: 99%

“…Sitnov et al () proposed to use modules similar to the original TS07D FAC basis functions shifted in latitude to fill the possible gap between R1 and R2 distributions. In this study, following Sitnov et al () and Stephens et al (), we describe the FAC system using 16 basis functions with the first two Fourier harmonics ( l =1,2) for R1 and R2, as well as their latitude‐shifted clones.…”

Section: Methodsmentioning

confidence: 99%

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Signatures of Nonideal Plasma Evolution During Substorms Obtained by Mining Multimission Magnetometer Data

et al. 2019

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Substorm-type evolution of the Earth's magnetosphere is investigated by mining more than two decades of spaceborne magnetometer data from multiple missions including the first two years (2016)(2017) of the Magnetospheric MultiScale mission. This investigation reveals interesting features of plasma evolution distinct from ideal magnetohydrodynamics (MHD) behavior: X-lines, thin current sheets, and regions with the tailward gradient of the equatorial magnetic field B z . X-lines are found to form mainly beyond 20 R E , but for strong driving, with the solar wind electric field exceeding ∼ 5mV/m, they may come closer. For substorms with weaker driving, X-lines may be preceded by redistribution of the magnetic flux in the tailward B z gradient regions, similar to the magnetic flux release instability discovered earlier in PIC and MHD simulations as a precursor mechanism of the reconnection onset. Current sheets in the growth phase may be as thin as 0.2 R E , comparable to the thermal ions gyroradius, and at the same time, as long as 15 R E . Such an aspect ratio is inconsistent with the isotropic force balance for observed magnetic field configurations. These findings can help resolve kinetic mechanisms of substorm dipolarizations and adjust kinetic generalizations of global MHD models of the magnetosphere. They can also guide and complement microscale analysis of nonideal effects. Plain Language SummaryThe sun emits a steam of charged particles called the solar wind that flows past the Earth interacting with the planet's dipole magnetic field. This stretches the dipolar magnetic field away from the sun on the nightside of the planet storing energy in the stretched field. Once every few hours, this stretched configuration suddenly becomes more dipolar bringing particles and magnetic flux closer to the planet and powering aurora in the polar regions. During these processes, termed substorms, the gas of charged particles, protons, and electrons trapped by the dipole and known as plasma, behaves largely as a perfectly conducting fluid. However, only deviations from this ideal conducting plasma behavior can explain the substorm mechanisms. We mine two decades of spacecraft magnetometer data from multiple missions to form swarms of thousands of synthetic probes. They help reveal effects of nonideal plasma evolution during substorms, which cannot be captured by direct in situ observations because of their extreme paucity.However, more than half a century ago, while examining the magnetospheric convection cycle, Dungey (1961) concluded that there are regions with topological singularities of the magnetic field, where ideal MHD

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Section: Methodsmentioning

confidence: 86%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Signatures of Nonideal Plasma Evolution During Substorms Obtained by Mining Multimission Magnetometer Data

et al. 2019

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“…In this test example we set IMF B = +5 nT; it should also be noted in passing that, due to the assumed linear dependence of the model field on the IMF B (equations (6)- (7)), reversing the IMF B orientation does not affect the shape of the internal equatorial B distribution nor its absolute magnitude but only reverses its polarity. The cause of the effect is not clear; it may be of either internal (such as the convection asymmetry, e.g., Spence & Kivelson, 1993;Sitnov et al, 2017) or external (IMF spiral structure) origin, or both. First, the induced B is not limited to only the nightside but extends throughout the entire equatorial magnetosphere.…”

Section: Global Modeling Resultsmentioning

confidence: 99%

Magnetospheric “Penetration” of IMF Viewed Through the Lens of an Empirical RBF Modeling

Tsyganenko

Andreeva

2020

JGR Space Physics

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The spiral structure of the interplanetary magnetic field (IMF) is known to induce intramagnetospheric azimuthal magnetic field B , which strongly correlates with the IMF B . We reconstruct this effect for the first time in 3-D, using a large set of data taken in the near/inner magnetosphere and a flexible magnetic field model based on expansions in radial basis functions (RBF). The RBF model serves here as a magnifying glass with tunable resolution, focused on the specific region of interest. In this study, we used it to explore the IMF-induced B both on a global scale (i.e., for the entire range of local times) and in the night sector only, to better visualize details in the region with the strongest "penetration" magnitude. The induced B was found to maximize on the nightside at distances R ∼10-12 R E , where it concentrates around the solar-magnetic equator and bifurcates into a pair of peaks located in predawn and postdusk sectors. The B "penetration" is associated with the IMF-induced asymmetry of field-aligned currents at the plasma sheet boundary. Even on a statistical level, the peak values of the induced B can substantially exceed the external IMF B . The effect is significantly stronger under southward IMF B z conditions and grows with increasing geodipole tilt angle. Key Points: • Global/local 3-D distributions of IMF-induced B are derived in closed field line domain using a new technique and large multiyear database • The induced B maximizes near SM equator at Xsm ∼ −10 R E where it splits into a pair of duskside/dawnside peaks and can significantly exceed IMF B • The effect is associated with asymmetry of Birkeland currents and increases under southward IMF

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“…The validation results for the 8 March 2009 substorm, in particular Figure 2t showing the comparison with GOES-11 data, demonstrate that while our method initially reconstructs the dipolarization signatures during Figure 1 respectively. (c and d) The square root of the sum of the squared amplitude coefficients for the R1 and R2 field-aligned current (FAC) modules, respectively (Sitnov, Stephens, et al, 2017). (e) The equatorial current sheet (CS) half thickness parameter for the thick CS in green and the thin current sheet (TCS) in orange.…”

Section: 1029/2018ja025843mentioning

confidence: 99%

Global Empirical Picture of Magnetospheric Substorms Inferred From Multimission Magnetometer Data

et al. 2019

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Magnetospheric substorms represent key explosive processes in the interaction of the Earth's magnetosphere with the solar wind, and their understanding and modeling are critical for space weather forecasting. During substorms, the magnetic field on the nightside is first stretched in the antisunward direction and then it rapidly contracts earthward bringing hot plasmas from the distant space regions into the inner magnetosphere, where they contribute to geomagnetic storms and Joule dissipation in the polar ionosphere, causing impressive splashes of aurora. Here we show for the first time that mining millions of spaceborne magnetometer data records from multiple missions allows one to reconstruct the global 3‐D picture of these stretching and dipolarization processes. Stretching results in the formation of a thin (less than the Earth's radius) and strong current sheet, which is diverted into the ionosphere during dipolarization. In the meantime, the dipolarization signal propagates further into the inner magnetosphere resulting in the accumulation of a longer lived current there, giving rise to a protogeomagnetic storm. The global 3‐D structure of the corresponding substorm currents including the substorm current wedge is reconstructed from data.

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Spatial Structure and Asymmetries of Magnetospheric Currents Inferred from High‐Resolution Empirical Geomagnetic Field Models

Cited by 15 publications

References 66 publications

Signatures of Nonideal Plasma Evolution During Substorms Obtained by Mining Multimission Magnetometer Data

Signatures of Nonideal Plasma Evolution During Substorms Obtained by Mining Multimission Magnetometer Data

Magnetospheric “Penetration” of IMF Viewed Through the Lens of an Empirical RBF Modeling

Global Empirical Picture of Magnetospheric Substorms Inferred From Multimission Magnetometer Data

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