scholarly journals A quantitative study of magnetospheric magnetic field line deformation by a two-loop substorm current wedge

2015 ◽  
Vol 33 (4) ◽  
pp. 505-517 ◽  
Author(s):  
A. V. Nikolaev ◽  
V. A. Sergeev ◽  
N. A. Tsyganenko ◽  
M. V. Kubyshkina ◽  
H. Opgenoorth ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Geomagnetic Latitude ◽  
Current Loop ◽  
Loop Model ◽  
Total Current ◽  
Substorm Current Wedge ◽  
Secondary Importance ◽  
Background Magnetic Field ◽  
Auroral Expansion ◽  
Current Wedge

Abstract. Substorm current wedge (SCW) formation is associated with global magnetic field reconfiguration during substorm expansion. We combine a two-loop model SCW (SCW2L) with a background magnetic field model to investigate distortion of the ionospheric footpoint pattern in response to changes of different SCW2L parameters. The SCW-related plasma sheet footprint shift results in formation of a pattern resembling an auroral bulge, the poleward expansion of which is controlled primarily by the total current in the region 1 sense current loop (I1). The magnitude of the footprint latitudinal shift may reach ∼ 10° corrected geomagnetic latitude (CGLat) during strong substorms (I1= 2 MA). A strong helical magnetic field around the field-aligned current generates a surge-like region with embedded spiral structures, associated with a westward traveling surge (WTS) at the western end of the SCW. The helical field may also contribute to rotation of the ionospheric projection of narrow plasma streams (auroral streamers). Other parameters, including the total current in the second (region 2 sense) loop, were found to be of secondary importance. Analyzing two consecutive dipolarizations on 17 March 2010, we used magnetic variation data obtained from a dense midlatitude ground network and several magnetospheric spacecraft, as well as the adaptive AM03 model, to specify SCW2L parameters, which allowed us to predict the magnitude of poleward auroral expansion. Auroral observations made during the two substorm activations demonstrate that the SCW2L combined with the AM03 model nicely describes the azimuthal progression and the observed magnitude of the auroral expansion. This finding indicates that the SCW-related distortions are responsible for much of the observed global development of bright auroras.

scholarly journals Development and validation of inversion technique for substorm current wedge using ground magnetic field data

2014 ◽  
Vol 119 (3) ◽  
pp. 1909-1924 ◽  
Author(s):  
Xiangning Chu ◽  
Tung-Shin Hsu ◽  
Robert L. McPherron ◽  
Vassilis Angelopoulos ◽  
Zuyin Pu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Data ◽  
Substorm Current Wedge ◽  
Magnetic Field Data ◽  
Inversion Technique ◽  
Ground Magnetic ◽  
Development And Validation ◽  
Current Wedge

The response of ionospheric convection in the polar cap to substorm activity

1995 ◽  
Vol 13 (2) ◽  
pp. 147-158 ◽  
Author(s):  
M. Lester ◽  
M. Lockwood ◽  
T. K. Yeoman ◽  
S. W. H. Cowley ◽  
H. Lühr ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Flux ◽  
Neutral Line ◽  
Flow Reversal ◽  
Polar Cap ◽  
Substorm Current Wedge ◽  
Expansion Phase ◽  
Ionospheric Convection ◽  
Eiscat Radar ◽  
Current Wedge

Abstract. We report multi-instrument observations during an isolated substorm on 17 October 1989. The EISCAT radar operated in the SP-UK-POLI mode measuring ionospheric convection at latitudes 71°λ-78°λ. SAMNET and the EISCAT Magnetometer Cross provide information on the timing of substorm expansion phase onset and subsequent intensifications, as well as the location of the field aligned and ionospheric currents associated with the substorm current wedge. IMP-8 magnetic field data are also included. Evidence of a substorm growth phase is provided by the equatorward motion of a flow reversal boundary across the EISCAT radar field of view at 2130 MLT, following a southward turning of the interplanetary magnetic field (IMF). We infer that the polar cap expanded as a result of the addition of open magnetic flux to the tail lobes during this interval. The flow reversal boundary, which is a lower limit to the polar cap boundary, reached an invariant latitude equatorward of 71°λ by the time of the expansion phase onset. A westward electrojet, centred at 65.4°λ, occurred at the onset of the expansion phase. This electrojet subsequently moved poleward to a maximum of 68.1°λ at 2000 UT and also widened. During the expansion phase, there is evidence of bursts of plasma flow which are spatially localised at longitudes within the substorm current wedge and which occurred well poleward of the westward electrojet. We conclude that the substorm onset region in the ionosphere, defined by the westward electrojet, mapped to a part of the tail radially earthward of the boundary between open and closed magnetic flux, the "distant" neutral line. Thus the substorm was not initiated at the distant neutral line, although there is evidence that it remained active during the expansion phase. It is not obvious whether the electrojet mapped to a near-Earth neutral line, but at its most poleward, the expanded electrojet does not reach the estimated latitude of the polar cap boundary.

scholarly journals Global manifestations of a substorm onset observed by a multi-satellite and ground station network

2006 ◽  
Vol 24 (12) ◽  
pp. 3491-3496 ◽  
Author(s):  
H. Wang ◽  
S. Y. Ma ◽  
H. Lühr ◽  
Z. X. Liu ◽  
Z. Y. Pu ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Substorm Onset ◽  
Double Star ◽  
Auroral Ionosphere ◽  
Substorm Current Wedge ◽  
Station Network ◽  
Ground Station ◽  
Auroral Breakup ◽  
Current Wedge

Abstract. With a favorable constellation of spacecraft and ground stations, a study is made on the global manifestations of a substorm onset. The onset occurred simultaneously and conjugately in both hemispheres, confirmed by observations of the auroral breakup from IMAGE FUV-WIC and a sudden intensification of a westward electrojet from ground-based magnetometers. Concurrently with the onset, field-aligned and Hall currents in the auroral ionosphere are observed by CHAMP, which are consistent with the signature of a Harang discontinuity. Immediately after the onset a magnetic field dipolarization is clearly observed by Double Star TC-1, located near the central magnetotail and subsequently, by the Cluster quartet. The observations can be explained by a dawnward propagation of the substorm current wedge at a speed of about 300 km/s.

Parametric excitation of magnetoacoustic waves by a pump magnetic field in a high-β plasma

1977 ◽  
Vol 17 (1) ◽  
pp. 93-103 ◽  
Author(s):  
N. F. Cramer
Keyword(s):  
Magnetic Field ◽  
Parametric Excitation ◽  
Acoustic Waves ◽  
Magnetic Pressure ◽  
Gas Pressure ◽  
Alfven Wave ◽  
Fast Wave ◽  
Magnetoacoustic Waves ◽  
Background Magnetic Field ◽  
The Waves

The parametric excitation of slow, intermediate (Alfvén) and fast magneto-acoustic waves by a modulated spatially non-uniform magnetic field in a plasma with a finite ratio of gas pressure to magnetic pressure is considered. The waves are excited in pairs, either pairs of the same mode, or a pair of different modes. The growth rates of the instabilities are calculated and compared with the known result for the Alfvén wave in a zero gas pressure plasma. The only waves that are found not to be excited are the slow plus fast wave pair, and the intermediate plus slow or fast wave pair (unless the waves have a component of propagation direction perpendicular to both the background magnetic field and the direction of non-uniformity of the field).

scholarly journals Network community structure of substorms using SuperMAG magnetometers

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
L. Orr ◽  
S. C. Chapman ◽  
J. W. Gjerloev ◽  
W. Guo
Keyword(s):  
Large Scale ◽  
Three Dimensional ◽  
Easy Access ◽  
Directed Network ◽  
Coherent System ◽  
Dimensional System ◽  
Ionospheric Currents ◽  
Substorm Current Wedge ◽  
Spatially Extended ◽  
Current Wedge

AbstractGeomagnetic substorms are a global magnetospheric reconfiguration, during which energy is abruptly transported to the ionosphere. Central to this are the auroral electrojets, large-scale ionospheric currents that are part of a larger three-dimensional system, the substorm current wedge. Many, often conflicting, magnetospheric reconfiguration scenarios have been proposed to describe the substorm current wedge evolution and structure. SuperMAG is a worldwide collaboration providing easy access to ground based magnetometer data. Here we show application of techniques from network science to analyze data from 137 SuperMAG ground-based magnetometers. We calculate a time-varying directed network and perform community detection on the network, identifying locally dense groups of connections. Analysis of 41 substorms exhibit robust structural change from many small, uncorrelated current systems before substorm onset, to a large spatially-extended coherent system, approximately 10 minutes after onset. We interpret this as strong indication that the auroral electrojet system during substorm expansions is inherently a large-scale phenomenon and is not solely due to many meso-scale wedgelets.

New technique to diagnose the geomagnetic field based on the single circular current loop model

2020 ◽  
Author(s):  
Zhaojin Rong ◽  
Yong Wei ◽  
Masatoshi Yamauchi ◽  
Wenyao Xu ◽  
Dali Kong ◽  
...  
Keyword(s):  
Geomagnetic Field ◽  
New Technique ◽  
Current Loop ◽  
Loop Model ◽  
Circular Current

On the existence of compressional MHD oscillations in an inhomogeneous magnetoplasma

1990 ◽  
Vol 44 (2) ◽  
pp. 361-375 ◽  
Author(s):  
Andrew N. Wright
Keyword(s):  
Magnetic Field ◽  
Wave Equation ◽  
Density Distribution ◽  
Cold Plasma ◽  
Wave Equations ◽  
Perturbation Field ◽  
Plasma Density Distribution ◽  
Background Magnetic Field ◽  
Transverse Fields ◽  
The Magnetic Field

In a cold plasma the wave equation for solely compressional magnetic field perturbations appears to decouple in any surface orthogonal to the background magnetic field. However, the compressional fields in any two of these surfaces are related to each other by the condition that the perturbation field b be divergence-free. Hence the wave equations in these surfaces are not truly decoupled from one another. If the two solutions happen to be ‘matched’ (i.e. V.b = 0) then the medium may execute a solely compressional oscillation. If the two solutions are unmatched then transverse fields must evolve. We consider two classes of compressional solutions and derive a set of criteria for when the medium will be able to support pure compressional field oscillations. These criteria relate to the geometry of the magnetic field and the plasma density distribution. We present the conditions in such a manner that it is easy to see if a given magnetoplasma is able to executive either of the compressional solutions we investigate.

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