Relation between the ring current and the tail current during magnetic storms

Abstract. We study the dynamics of the magnetospheric large-scale current systems during storms by using three different magnetospheric magnetic field models: the paraboloid, event-oriented, and Tsyganenko T01 models. We have modelled two storm events, one moderate storm on 25-26 June 1998, when Dst reached -120nT and one intense storm on 21-23 October 1999, when Dst dropped to -250nT. We compare the observed magnetic field from GOES 8, GOES 9, and GOES 10, Polar and Geotail satellites with the magnetic field given by the three models to estimate their reliability. All models demonstrated quite good agreement with observations. Since it is difficult to measure exactly the relative contributions from different current systems to the Dst index, we compute the contributions from ring, tail and magnetopause currents given by the three magnetic field models. We discuss the dependence of the obtained contributions to the Dst index in relation to the methods used in constructing the models. All models show a significant tail current contribution to the Dst index, comparable to the ring current contribution during moderate storms. The ring current becomes the major Dst source during intense storms.

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Distortions of the magnetic field by storm-time current systems in Earth's magnetosphere

Annales Geophysicae ◽

10.5194/angeo-28-123-2010 ◽

2010 ◽

Vol 28 (1) ◽

pp. 123-140 ◽

Cited By ~ 36

Author(s):

N. Yu. Ganushkina ◽

M. W. Liemohn ◽

M. V. Kubyshkina ◽

R. Ilie ◽

H. J. Singer

Keyword(s):

Magnetic Field ◽

Ring Current ◽

Geostationary Orbit ◽

Modeling Framework ◽

Inner Magnetosphere ◽

Tail Current ◽

Modeling Approaches ◽

Intense Storm ◽

The Magnetic Field ◽

Moderate Storm

Abstract. Magnetic field and current system changes in Earth's inner magnetosphere during storm times are studied using two principally different modeling approaches: on one hand, the event-oriented empirical magnetic field model, and, on the other, the Space Weather Modeling Framework (SWMF) built around a global MHD simulation. Two storm events, one moderate storm on 6–7 November 1997 with Dst minimum about −120 nT and one intense storm on 21–23 October 1999 with Dst minimum about −250 nT were modeled. Both modeling approaches predicted a large ring current (first partial, later symmetric) contribution to the magnetic field perturbation for the intense storm. For the moderate storm, the tail current plays a dominant role in the event-oriented model results, while the SWMF results showed no strong tail current in the main phase, which resulted in a poorly timed storm peak relative to the observations. These results imply that the the development of a ring current depends on a strong force to inject the particles deep into the inner magnetosphere, and that the tail current is an important external source for the distortions of the inner magnetospheric magnetic field for both storms. Neither modeling approach was able to reproduce all the variations in the Bx and By components observed at geostationary orbit by GOES satellites during these two storms: the magnetopause current intensifications are inadequate, and the field-aligned currents are not sufficiently represented. While the event-oriented model reproduces rather well the Bz component at geostationary orbit, including the substorm-associated changes, the SWMF field is too dipolar at these locations. The empirical model is a useful tool for validation of the first-principle based models such as the SWMF.

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Long-term evolution of magnetospheric current systems during storms

Annales Geophysicae ◽

10.5194/angeo-22-1317-2004 ◽

2004 ◽

Vol 22 (4) ◽

pp. 1317-1334 ◽

Cited By ~ 46

Author(s):

N. Yu. Ganushkina ◽

T. I. Pulkkinen ◽

M. V. Kubyshkina ◽

H. J. Singer ◽

C. T. Russell

Keyword(s):

Magnetic Field ◽

Ring Current ◽

Geomagnetic Storms ◽

High Time Resolution ◽

Time Step ◽

Field Representation ◽

Dst Index ◽

Model Free ◽

Magnetospheric Configuration And Dynamics ◽

Current Systems

Abstract. We present a method to model the storm-time magnetospheric magnetic field using representations of the magnetic field arising from the various magnetospheric current systems. We incorporate the effects of magnetotail changes during substorms by introducing an additional localized thin current sheet into the Tsyganenko T89 model. To represent the storm-time ring current the T89 ring current is replaced by a bean-shaped current system, which has a cross section that is close to the observed distribution of trapped particles in the inner magnetosphere and has an eastward flowing inner and westward flowing outer components. In addition to the symmetric ring current, an asymmetric partial ring current is taken into account with closing Region 2 sense field-aligned currents. Magnetopause currents are varied in accordance with solar wind dynamic pressure variations. Three moderate geomagnetic storms when Dst reached about –150 nT and one big storm with Dst about –250 nT are modelled. The model free parameters are specified for each time step separately using observations from GOES 8 and 9, Polar, Interball and Geotail satellites and Dst measurements. The model gives a high time-resolution field representation of the large-scale magnetic field, and a very good reproduction of the Dst index. It is shown that the ring current is most important during intense storms, whereas the near-Earth tail currents contribute more to the Dst index than the ring current during moderate storms. Key words. Magnetospheric physics (Current systems; Magnetospheric configuration and dynamics; Storms and substorms)

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A note on the ring current in Saturn’s magnetosphere: Comparison of magnetic data obtained during the Pioneer-11 and Voyager-1 and -2 fly-bys

Annales Geophysicae ◽

10.5194/angeo-21-661-2003 ◽

2003 ◽

Vol 21 (3) ◽

pp. 661-669 ◽

Cited By ~ 20

Author(s):

E. J. Bunce ◽

S. W. H. Cowley

Keyword(s):

Magnetic Field ◽

Ring Current ◽

Current System ◽

Magnetic Data ◽

Total Current ◽

Planetary Magnetospheres ◽

Magnetospheric Configuration And Dynamics ◽

Magnetospheric Configuration ◽

First Time ◽

Current Systems

Abstract. We examine the residual (measured minus internal) magnetic field vectors observed in Saturn’s magnetosphere during the Pioneer-11 fly-by in 1979, and compare them with those observed during the Voyager-1 and -2 fly-bys in 1980 and 1981. We show for the first time that a ring current system was present within the magnetosphere during the Pioneer-11 encounter, which was qualitatively similar to those present during the Voyager fly-bys. The analysis also shows, however, that the ring current was located closer to the planet during the Pioneer-11 encounter than during the comparable Voyager-1 fly-by, reflecting the more com-pressed nature of the magnetosphere at the time. The residual field vectors have been fit using an adaptation of the current system proposed for Jupiter by Connerney et al. (1981a). A model that provides a reasonably good fit to the Pioneer-11 Saturn data extends radially between 6.5 and 12.5 RS (compared with a noon-sector magnetopause distance of 17 RS), has a north-south extent of 4 RS, and carries a total current of 9.6 MA. A corresponding model that provides a qualitatively similar fit to the Voyager data, determined previously by Connerney et al. (1983), extends radially between 8 and 15.5 RS (compared with a noon-sector magnetopause distance for Voyager-1 of 23–24 RS), has a north-south extent of 6 RS, and carries a total current of 11.5 MA.Key words. Magnetospheric physics (current systems, magnetospheric configuration and dynamics, planetary magnetospheres)

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The Geosynchronous Substorm

Convection and Substorms ◽

10.1093/oso/9780195085297.003.0016 ◽

1996 ◽

Author(s):

Charles F. Kennel

Keyword(s):

Magnetic Field ◽

Growth Phase ◽

Large Scale ◽

Current System ◽

Dynamic Pressure ◽

Geosynchronous Orbit ◽

Sudden Increase ◽

Tail Current ◽

Tightly Coupled ◽

The Cross

The reconnection model of substorms deals with the large-scale changes in the structure of the magnetosphere and tail as convection intensifies following a sudden increase in the dayside reconnection rate. The model has difficulty making statements relevant to the small scales that characterize auroral onset. However, there has been considerable progress in assembling high-resolution observations of the events in space that now appear to be tightly coupled to the dramatic auroral events that first defined the term substorm. We will call this clear and consistent ensemble the geosynchronous model of substorms, since most of it was first conceived from observations made on geostationary spacecraft. We will also include in this ensemble the recent observations made using the quasigeostationary spacecraft, AMPTE/CCE, and so, by the geosynchronous substorm, we really mean the substorm as it appears on the earth's nightside typically between 6 and, say, 10 RE downtail. The earth’s magnetic field at geosynchronous orbit is about 100 nT, some three times larger than in the tail lobes. Study of quiet field intervals singles out the dependence of the geosynchronous field on solar wind dynamic pressure, since the modulation due to changes in the direction of the interplanetary field is presumably negligible during quiet conditions. The periodic variations in the quiet field depend on local time, season, and orientation of the earth’s dipole axis relative to spacecraft location (McPherron and Barfield, 1980; Rufenach et al., 1992). Superposed on the quiet field are perturbations up to about 50 nT due to several magnetospheric current systems, including the magnetopause current, the ring current, and the cross-tail current; the most striking are due to changes in the cross-tail current system. Observations from geosynchronous orbit were the first to indicate that the nightside magnetic field becomes more “tail-like” during substorm growth phase, and more dipolar during the expansion phase. This simple observation is the foundation on which today’s elaborate geosynchronous substorm model rests. The geosynchronous field becomes progressively more “tail-like” as the cross-tail current system intensifies and/or moves earthward during the substorm growth phase (McPherron et al., 1975; Coleman and McPherron, 1976; McPherron, 1979; Kauffmann, 1987).

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Strong Southward and Northward Currents Observed in the Inner Plasma Sheet

10.5194/angeo-2019-56 ◽

2019 ◽

Author(s):

Yanyan Yang ◽

Chao Shen ◽

Yong Ji

Keyword(s):

Magnetic Field ◽

Plasma Sheet ◽

Ring Current ◽

Generation Mechanism ◽

Storm Events ◽

Current Generation ◽

Inner Magnetosphere ◽

Latitude Region ◽

Field Lines ◽

The Magnetic Field

Abstract. It is generally believed that field aligned currents (FACs) and the ring current (RC) are two dominant parts of the inner magnetosphere. However, using the Cluster spacecraft crossing of the pre-midnight inner plasma sheet in the latitude region between 10° N and 30° N, it is found that, during large storm events, in addition to FACs and the RC, there also exist strong southward and northward currents, which cannot be FACs, because the magnetic field in these regions is mainly along the XY plane. Detailed investigation shows that both magnetic field lines (MFLs) and currents in these regions highly fluctuate. When the curvature of MFLs changes direction in the XY plane, the current also alternatively switches between southward and northward. Further analysis of the current generation mechanism indicates that the most reasonable candidate for the origin of these southward and northward currents is the curvature drift of energetic particles.

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Connecting magnetic fields from sub-galactic scale to clusters of galaxies and beyond with cosmological MHD simulations

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316006396 ◽

2015 ◽

Vol 11 (A29B) ◽

pp. 699-699

Author(s):

Klaus Dolag ◽

Alexander M. Beck ◽

Alexander Arth

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Heat Transport ◽

Galaxy Clusters ◽

Large Scale ◽

High Redshift ◽

Galactic Halos ◽

Rotation Measure ◽

The Magnetic Field ◽

Good Agreement

AbstractUsing the MHD version of Gadget3 (Stasyszyn, Dolag & Beck 2013) and a model for the seeding of magnetic fields by supernovae (SN), we performed simulations of the evolution of the magnetic fields in galaxy clusters and study their effects on the heat transport within the intra cluster medium (ICM). This mechanism – where SN explosions during the assembly of galaxies provide magnetic seed fields – has been shown to reproduce the magnetic field in Milky Way-like galactic halos (Beck et al. 2013). The build up of the magnetic field at redshifts before z = 5 and the accordingly predicted rotation measure evolution are also in good agreement with current observations. Such magnetic fields present at high redshift are then transported out of the forming protogalaxies into the large-scale structure and pollute the ICM (in a similar fashion to metals transport). Here, complex velocity patterns, driven by the formation process of cosmic structures are further amplifying and distributing the magnetic fields. In galaxy clusters, the magnetic fields therefore get amplified to the observed μG level and produce the observed amplitude of rotation measures of several hundreds of rad/m2. We also demonstrate that heat conduction in such turbulent fields on average is equivalent to a suppression factor around 1/20th of the classical Spitzer value and in contrast to classical, isotropic heat transport leads to temperature structures within the ICM compatible with observations (Arth et al. 2014).

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Statistical analysis of storm-time near-Earth current systems

Annales Geophysicae ◽

10.5194/angeo-33-965-2015 ◽

2015 ◽

Vol 33 (8) ◽

pp. 965-982 ◽

Cited By ~ 8

Author(s):

M. W. Liemohn ◽

R. M. Katus ◽

R. Ilie

Keyword(s):

Electric Field ◽

Ring Current ◽

Recovery Phase ◽

Hot Electron ◽

Early Recovery ◽

Superposed Epoch Analysis ◽

Tail Current ◽

Near Earth Space ◽

Epoch Analysis ◽

Current Systems

Abstract. Currents from the Hot Electron and Ion Drift Integrator (HEIDI) inner magnetospheric model results for all of the 90 intense storms (disturbance storm-time (Dst) minimum < −100 nT) from solar cycle 23 (1996–2005) are calculated, presented, and analyzed. We have categorized these currents into the various systems that exist in near-Earth space, specifically the eastward and westward symmetric ring current, the partial ring current, the banana current, and the tail current. The current results from each run set are combined by a normalized superposed epoch analysis technique that scales the timeline of each phase of each storm before summing the results. It is found that there is a systematic ordering to the current systems, with the asymmetric current systems peaking during storm main phase (tail current rising first, then the banana current, followed by the partial ring current) and the symmetric current systems peaking during the early recovery phase (westward and eastward symmetric ring current having simultaneous maxima). The median and mean peak amplitudes for the current systems ranged from 1 to 3 MA, depending on the setup configuration used in HEIDI, except for the eastward symmetric ring current, for which the mean never exceeded 0.3 MA for any HEIDI setup. The self-consistent electric field description in HEIDI yielded larger tail and banana currents than the Volland–Stern electric field, while the partial and symmetric ring currents had similar peak values between the two applied electric field models.

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Relation of polar auroral arcs to magnetotail twisting and IMF rotation: a systematic MHD simulation study

Annales Geophysicae ◽

10.5194/angeo-22-951-2004 ◽

2004 ◽

Vol 22 (3) ◽

pp. 951-970 ◽

Cited By ~ 44

Author(s):

A. Kullen ◽

P. Janhunen

Keyword(s):

Magnetic Field ◽

Simulation Study ◽

Large Scale ◽

Detailed Examination ◽

Mhd Simulation ◽

Mhd Simulations ◽

Sign Change ◽

Auroral Arcs ◽

Good Agreement ◽

Imf Clock Angle

Abstract. We investigate with the help of a magnetohydrodynamic (MHD) model how the large-scale topology of the magnetosphere develops for a constant interplanetary magnetic field (IMF) with different IMF clock angles and for an IMF By sign change during northward IMF. A detailed examination of the topological changes in the tail and the ionosphere for different IMF conditions shows a good agreement with observational results. The MHD simulations for different constant IMF clock angle cases show the expected field-line bending and tail twisting for nonzero IMF By. The tail becomes longer and at its tailward end stronger twisted for IMF Bz>∣By∣ than for IMF Bz

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Storm-time ring current: model-dependent results

Annales Geophysicae ◽

10.5194/angeo-30-177-2012 ◽

2012 ◽

Vol 30 (1) ◽

pp. 177-202 ◽

Cited By ~ 23

Author(s):

N. Yu. Ganushkina ◽

M. W. Liemohn ◽

T. I. Pulkkinen

Keyword(s):

Magnetic Field ◽

Electric Field ◽

Boundary Conditions ◽

Electric Fields ◽

Ring Current ◽

Current Model ◽

Current Data ◽

Storm Events ◽

Boundary Location ◽

Field Lines

Abstract. The main point of the paper is to investigate how much the modeled ring current depends on the representations of magnetic and electric fields and boundary conditions used in simulations. Two storm events, one moderate (SymH minimum of −120 nT) on 6–7 November 1997 and one intense (SymH minimum of −230 nT) on 21–22 October 1999, are modeled. A rather simple ring current model is employed, namely, the Inner Magnetosphere Particle Transport and Acceleration model (IMPTAM), in order to make the results most evident. Four different magnetic field and two electric field representations and four boundary conditions are used. We find that different combinations of the magnetic and electric field configurations and boundary conditions result in very different modeled ring current, and, therefore, the physical conclusions based on simulation results can differ significantly. A time-dependent boundary outside of 6.6 RE gives a possibility to take into account the particles in the transition region (between dipole and stretched field lines) forming partial ring current and near-Earth tail current in that region. Calculating the model SymH* by Biot-Savart's law instead of the widely used Dessler-Parker-Sckopke (DPS) relation gives larger and more realistic values, since the currents are calculated in the regions with nondipolar magnetic field. Therefore, the boundary location and the method of SymH* calculation are of key importance for ring current data-model comparisons to be correctly interpreted.

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Modelling of the ring current in Saturn's magnetosphere

Annales Geophysicae ◽

10.5194/angeo-22-653-2004 ◽

2004 ◽

Vol 22 (2) ◽

pp. 653-659 ◽

Cited By ~ 38

Author(s):

G. Giampieri ◽

M. K. Dougherty

Keyword(s):

Magnetic Field ◽

Ring Current ◽

Current Model ◽

Temporal Variations ◽

Data Sets ◽

Data Set ◽

Equatorial Current ◽

The Difference ◽

Current Systems ◽

The Magnetic Field

Abstract. The existence of a ring current inside Saturn's magnetosphere was first suggested by Smith et al. (1980) and Ness et al. (1981, 1982), in order to explain various features in the magnetic field observations from the Pioneer 11 and Voyager 1 and 2 spacecraft. Connerney et al. (1983) formalized the equatorial current model, based on previous modelling work of Jupiter's current sheet and estimated its parameters from the two Voyager data sets. Here, we investigate the model further, by reconsidering the data from the two Voyager spacecraft, as well as including the Pioneer 11 flyby data set. First, we obtain, in closed form, an analytic expression for the magnetic field produced by the ring current. We then fit the model to the external field, that is the difference between the observed field and the internal magnetic field, considering all the available data. In general, through our global fit we obtain more accurate parameters, compared to previous models. We point out differences between the model's parameters for the three flybys, and also investigate possible deviations from the axial and planar symmetries assumed in the model. We conclude that an accurate modelling of the Saturnian disk current will require taking into account both of the temporal variations related to the condition of the magnetosphere, as well as non-axisymmetric contributions due to local time effects. Key words. Magnetospheric physics (current systems; planetary magnetospheres; plasma sheet)

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