Long-term evolution of magnetospheric current systems during storms

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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Morphology of the ring current derived from magnetic field observations

Annales Geophysicae ◽

10.5194/angeo-22-1267-2004 ◽

2004 ◽

Vol 22 (4) ◽

pp. 1267-1295 ◽

Cited By ~ 105

Author(s):

G. Le ◽

C. T. Russell ◽

K. Takahashi

Keyword(s):

Magnetic Field ◽

Field Data ◽

Ring Current ◽

Current System ◽

Local Times ◽

Unexpected Result ◽

Magnetic Field Data ◽

Dst Index ◽

Ring Currents ◽

Magnetospheric Configuration And Dynamics

Abstract. Our examination of the 20 years of magnetospheric magnetic field data from ISEE, AMPTE/CCE and Polar missions has allowed us to quantify how the ring current flows and closes in the magnetosphere at a variety of disturbance levels. Using intercalibrated magnetic field data from the three spacecraft, we are able to construct the statistical magnetic field maps and derive 3-dimensional current density by the simple device of taking the curl of the statistically determined magnetic field. The results show that there are two ring currents, an inner one that flows eastward at ~3 RE and a main westward ring current at ~4–7 RE for all levels of geomagnetic disturbances. In general, the in-situ observations show that the ring current varies as the Dst index decreases, as we would expect it to change. An unexpected result is how asymmetric it is in local time. Some current clearly circles the magnetosphere but much of the energetic plasma stays in the night hemisphere. These energetic particles appear not to be able to readily convect into the dayside magnetosphere. During quiet times, the symmetric and partial ring currents are similar in strength (~0.5MA) and the peak of the westward ring current is close to local midnight. It is the partial ring current that exhibits most drastic intensification as the level of disturbances increases. Under the condition of moderate magnetic storms, the total partial ring current reaches ~3MA, whereas the total symmetric ring current is ~1MA. Thus, the partial ring current contributes dominantly to the decrease in the Dst index. As the ring current strengthens the peak of the partial ring current shifts duskward to the pre-midnight sector. The partial ring current is closed by a meridional current system through the ionosphere, mainly the field-aligned current, which maximizes at local times near the dawn and dusk. The closure currents flow in the sense of region-2 field-aligned currents, downward into the ionosphere near the dusk and upward out of the ionosphere near the dawn. Key words. Magnetospheric physics (current systems; storms and substorms; magnetospheric configuration and dynamics)

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

Annales Geophysicae ◽

10.5194/angeo-23-523-2005 ◽

2005 ◽

Vol 23 (2) ◽

pp. 523-533 ◽

Cited By ~ 36

Author(s):

V. V. Kalegaev ◽

N. Y. Ganushkina ◽

T. I. Pulkkinen ◽

M. V. Kubyshkina ◽

H. J. Singer ◽

...

Keyword(s):

Magnetic Field ◽

Large Scale ◽

Ring Current ◽

Storm Events ◽

Dst Index ◽

Tail Current ◽

Current Contribution ◽

Intense Storm ◽

Current Systems ◽

Good Agreement

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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Afternoon mid-latitude current system and low-latitude geomagnetic field asymmetry during geomagnetic storms

Annales Geophysicae ◽

10.1007/s00585-997-1537-5 ◽

1997 ◽

Vol 15 (12) ◽

pp. 1537-1547 ◽

Cited By ~ 13

Author(s):

A. Grafe ◽

P. A. Bespalov ◽

V. Y. Trakhtengerts ◽

A. G. Demekhov

Keyword(s):

Magnetic Field ◽

Ring Current ◽

Geomagnetic Storms ◽

Current System ◽

Three Dimensional ◽

Low Latitude ◽

Electrojet Current ◽

The Relationship ◽

Current Systems ◽

Correlative Relationship

Abstract. For four geomagnetic storms of middle intensity the relationship between the low-latitude magnetic field asymmetry using ASY indices and the intensity of the auroral eastward and westward electrojet was considered. It was asked whether there exists a connection between ASY and the eastward electrojet. To answer this question equivalent current systems were estimated in mid-latitudes. It was found that the observations obviously show no correlative relationship between the low-latitude magnetic-field asymmetry and the eastward electrojet, whereas one exists between ASY and the westward electrojet. To explain the generally accepted common three-dimensional current system between the partial ring current and the eastward electrojet, a condensor model of the three-dimensional current system was developed. It could be shown that the short periodic variations of the partial ring current are shielded by the condensor and cannot influence the eastward-electrojet current.

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First current density measurements in the ring current region using simultaneous multi-spacecraft CLUSTER-FGM data

Annales Geophysicae ◽

10.5194/angeo-23-1849-2005 ◽

2005 ◽

Vol 23 (5) ◽

pp. 1849-1865 ◽

Cited By ~ 53

Author(s):

C. Vallat ◽

I. Dandouras ◽

M. Dunlop ◽

A. Balogh ◽

E. Lucek ◽

...

Keyword(s):

Magnetic Field ◽

Current Density ◽

Ring Current ◽

Magnetic Activity ◽

Activity Level ◽

Local Current Density ◽

Magnetospheric Configuration And Dynamics ◽

Local Current ◽

Current Region ◽

First Time

Abstract. The inner magnetosphere's current mapping is one of the key elements for current loop closure inside the entire magnetosphere. A method for directly computing the current is the multi-spacecraft curlometer technique, which is based on the application of Maxwell-Ampère's law. This requires the use of four-point magnetic field high resolution measurements. The FGM experiment on board the four Cluster spacecraft allows, for the first time, an instantaneous calculation of the magnetic field gradients and thus a measurement of the local current density. This technique requires, however, a careful study concerning all the factors that can affect the accuracy of the J estimate, such as the tetrahedral geometry of the four spacecraft, or the size and orientation of the current structure sampled. The first part of this paper is thus providing a detailed analysis of the method accuracy, and points out the limitations of this technique in the region of interest. The second part is an analysis of the ring current region, which reveals, for the first time, the large latitudinal extent of the ring current, for all magnetic activity levels, as well as the latitudinal evolution of the perpendicular (and parallel) components of the current along the diffuse auroral zone. Our analysis also points out the sharp transition between two distinct plasma regions, with the existence of high diamagnetic currents at the interface, as well as the filamentation of the current inside the inner plasma sheet. A statistical study over multiple perigee passes of Cluster (at about 4 RE from the Earth) reveals the azimuthal extent of the partial ring current. It also reveals that, at these distances and all along the evening sector, there isn't necessarily a strong dependence of the local current density value on the magnetic activity level. This is a direct consequence of the ring current morphology evolution, as well as the relative positioning of the spacecraft with respect to the bulk of the ring current. It also proves the existence of a substantial ring current at these distances, all over the evening and the post-midnight sector. Keywords. Magnetospheric physics (Current systems; Energetic particles, trapped; Magnetospheric configuration and dynamics)

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A quantitative model of the magnetosphere with poloidal vector fields

Annales Geophysicae ◽

10.1007/s00585-998-1557-9 ◽

1998 ◽

Vol 16 (12) ◽

pp. 1557-1566 ◽

Cited By ~ 3

Author(s):

J. C. Kosik

Keyword(s):

Magnetic Field ◽

Vector Fields ◽

Ring Current ◽

Computer Time ◽

Quantitative Model ◽

Magnetospheric Configuration And Dynamics ◽

Current Region ◽

Magnetospheric Configuration ◽

Distant Field ◽

Dependent Field

Abstract. A quantitative model of the magnetospheric magnetic field is developed using poloidal vector fields. This formalism is applied to the ring current region, the distant field and the return currents. The tail model is similar to the unwarped model of Tsyganenko. Several sets of coefficients are obtained for different Kp through a fit of the NSSDC data base. Experimental ΔB contours and theoretical distributed currents contours are correctly described and are Kp-dependent. Field line topology problems and poor ring current description observed in models of similar complexity are avoided. Computer time has been kept reasonable and makes this model particularly adapted to intensive-type calculations.Key words. Magnetospheric physics (magnetospheric · configuration and dynamics).

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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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A Statistical Study on DH CMEs and Its Geoeffectiveness

ISRN Astronomy and Astrophysics ◽

10.1155/2013/129426 ◽

2013 ◽

Vol 2013 ◽

pp. 1-13 ◽

Cited By ~ 4

Author(s):

V. Vasanth ◽

S. Umapathy

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Wind Speed ◽

Field Component ◽

Geomagnetic Storms ◽

Solar Wind Speed ◽

Type Ii ◽

Dst Index ◽

Long Duration ◽

Type Ii Bursts

A detailed investigation on geoeffectiveness of CMEs associated with DH-type-II bursts observed during 1997–2008 is presented. The collected sample events are divided into two groups based on their association with CMEs related to geomagnetic storms Dst ≤−50 nT, namely, (i) geoeffective events and (ii) nongeoeffective events. We found that the geoeffective events have high starting frequency, low ending frequency, long duration, wider bandwidth, energetic flares, and CMEs than nongeoeffective events. The geoeffective events are found to have intense geomagnetic storm with mean Dst index (−150 nT). There exists good correlation between the properties of CMEs and flares for geoeffective events, while no clear correlation exists for nongeoeffective events. There exists a weak correlation for geoeffective events between (i) CME speed and Dst index (R=-0.51) and good correlation between (i) CME speed and solar wind speed (R=0.60), (ii) Dst index and solar wind speed (R=-0.64), and (iii) Dst index and southward magnetic field component (Bz) (R=0.80). From our study we conclude that the intense and long duration southward magnetic field component (Bz) and fast solar wind speed are responsible for geomagnetic storms, and the geomagnetic storms weakly depend on CME speed. About 22% (50/230) of the DH-type-II bursts are associated with geomagnetic storms. Therefore the DH-type-II bursts associated with energetic flares and CMEs are good indicator of geomagnetic storms.

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The Plasmasphere During Major Geomagnetic Storms: Analysis Of Trapped Particles In The Outer Radiation Belt

10.5194/egusphere-egu2020-265 ◽

2020 ◽

Author(s):

Jessy Matar ◽

Benoit Hubert ◽

Stan Cowley ◽

Steve Milan ◽

Zhonghua Yao ◽

...

Keyword(s):

Magnetic Field ◽

Electric Field ◽

Geomagnetic Field ◽

Radiation Belt ◽

Ring Current ◽

Geomagnetic Storms ◽

Outer Radiation Belt ◽

Trapped Particles ◽

The Earth ◽

Field Lines

<p> The coupling between the Earth&#8217;s magnetic field and the interplanetary magnetic field (IMF) transported by the solar wind results in a cycle of magnetic field lines opening and closing generally known as the Dungey substorm cycle, mostly governed by the process of magnetic reconnection. The geomagnetic field lines can therefore have either a closed or an open topology, i.e. lower latitude field lines are closed (map from southern ionosphere to the northern), while higher latitude field lines are open (map from one polar ionosphere into interplanetary space). Closed field lines can trap electrically charged particles that bounce between mirror points located in the North and South hemispheres while drifting in longitude around the Earth, forming the plasmasphere, the radiation belts and the ring current. The outer boundary of the plasmasphere is the plasmapause. Its location is mostly driven by the interplay of the corotation electric field of ionospheric origin, and the convection electric field that results from the interaction between the IMF and the geomagnetic field. At times of prolonged intense coupling between these fields, the response of the magnetosphere becomes global and a geomagnetic storm develops. The ring current created by the motion of the trapped energetic particles intensifies and then decays as the storm abates. This study aims to find a possible relationship between the evolution of the trapped population and the process of magnetic reconnection during storm times. The EUV instrument on board the NASA-IMAGE spacecraft observed the distribution of the trapped helium ions (He+) in the plasmasphere. We consider several cases of intense geomagnetic storms observed by the IMAGE satellite. We identify the plasmapause location (Lpp) during those cases. We find a strong correlation between the Dst index and Lpp. The ring current and the trapped particles are expected to vary during storms. We use the Tsyganenko magnetic field model to map the electric potential between the Heppner-Maynard boundary (HMB) in the ionosphere and the magnetosphere and estimate the voltage and electric field in the vicinity of the plasmapause. The ionospheric electric field is deduced from the ionospheric convection velocity measured by the SuperDARN (SD) radar network at high latitudes. The tangential electric field component of the moving plasmapause boundary is estimated from IMAGE-EUV observations of the plasmasphere and is compared with expectations based on the SD data. We combine measurements of the trapped population from IMAGE-EUV and IMAGE-FUV observations of the aurora to better understand and quantify the variability of the Earth's outer radiation belt during strong storms. The auroral precipitation at ionospheric latitude is studied using FUV imaging and compared to the He+ response during the storms.</p>

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Ring current decay time model during geomagnetic storms: a simple analytical approach

Annales Geophysicae ◽

10.5194/angeo-26-2543-2008 ◽

2008 ◽

Vol 26 (9) ◽

pp. 2543-2550 ◽

Cited By ~ 15

Author(s):

R. Monreal MacMahon ◽

C. Llop-Romero

Keyword(s):

Continuous Function ◽

Decay Time ◽

Ring Current ◽

Geomagnetic Storms ◽

Reference Model ◽

Empirical Work ◽

Injection Rate ◽

Storm Events ◽

Time Model ◽

Dst Index

Abstract. The ring current growth and decay, characterized by the Dst index, has been studied for thirty years using the Burton et al. (1975) equation. The original formula is based on the restriction of the DPS (Dessler, Parker, and Schoppke) theorem and assuming a constant decay time of particles. The decay time scale is important because the energy injection rate cannot be determined it without the knowledge of this parameter. In a previous work, instead of using a constant value, we introduced the decay time of particles in the energy rate balance equation as a continuous function of the absolute value of the pressure corrected Dst index to avoid the reported discontinuities determining it. Here, based on the DPS restriction, we extend our previous empirical work to obtain analytically the proposed continuous function considering losses due to a global resistive force as a product of viscous-like, and other related dissipation processes. We test our model predicting Dst for a couple of specific storm events and also comparing our results with forecasts of a good reference model appeared in the literature.

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