scholarly journals MMS Observation on the Cross‐Tail Current Sheet Roll‐up at the Dipolarization Front

2021 ◽  
Vol 126 (4) ◽  
Author(s):  
L. Q. Zhang ◽  
C. Wang ◽  
L. Dai ◽  
H. S. Fu ◽  
A. T. Y. Lui ◽  
...  
Keyword(s):  
Current Sheet ◽  
Tail Current ◽  
Dipolarization Front ◽  
The Cross

scholarly journals A physical explanation for the magnetic decrease ahead of dipolarization fronts

2015 ◽  
Vol 33 (10) ◽  
pp. 1301-1309 ◽  
Author(s):  
Z. H. Yao ◽  
J. Liu ◽  
C. J. Owen ◽  
C. Forsyth ◽  
I. J. Rae ◽  
...  
Keyword(s):  
Plasma Pressure ◽  
Current Loop ◽  
Tail Current ◽  
Dipolarization Front ◽  
Local Current ◽  
Order Of Magnitude ◽  
Closed Current ◽  
Field Aligned Current ◽  
The Cross ◽  
A Current

Abstract. Recent studies have shown that the ambient plasma in the near-Earth magnetotail can be compressed by the arrival of a dipolarization front (DF). In this paper we study the variations in the characteristics of currents flowing in this compressed region ahead of the DF, particularly the changes in the cross-tail current, using observations from the THEMIS satellites. Since we do not know whether the changes in the cross-tail current lead to a field-aligned current formation or just form a current loop in the magnetosphere, we thus use redistribution to represent these changes of local current density. We found that (1) the redistribution of the cross-tail current is a common feature preceding DFs; (2) the redistribution of cross-tail current is caused by plasma pressure gradient ahead of the DF and (3) the resultant net current redistributed by a DF is an order of magnitude smaller than the typical total current associated with a moderate substorm current wedge (SCW). Moreover, our results also suggest that the redistributed current ahead of the DF is closed by currents on the DF itself, forming a closed current loop around peaks in plasma pressure, what is traditionally referred to as a banana current.

scholarly journals Asymmetry in the Earth’s magnetotail neutral sheet rotation due to IMF $$B_y$$ sign?

2021 ◽  
Vol 8 (1) ◽  
Author(s):  
Timo Pitkänen ◽  
Anita Kullen ◽  
Lei Cai ◽  
Jong-Sun Park ◽  
Heikki Vanhamäki ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Interplanetary Magnetic Field ◽  
Current Sheet ◽  
The Sun ◽  
Neutral Sheet ◽  
Tail Current ◽  
Cluster Data ◽  
The Asymmetry ◽  
The Cross ◽  
Possible Cause

AbstractEvidence suggests that a non-zero dawn–dusk interplanetary magnetic field (IMF $$B_y$$ B y ) can cause a rotation of the cross-tail current sheet/neutral sheet around its axis aligned with the Sun–Earth line in Earth’s magnetotail. We use Geotail, THEMIS and Cluster data to statistically investigate how the rotation of the neutral sheet depends on the sign and magnitude of IMF $$B_y$$ B y . In our dataset, we find that in the tail range of $$-30<$$ - 30 < XGSM $$<-15$$ < - 15 $$R_{\mathrm{E}}$$ R E , the degree of the neutral sheet rotation is clearly smaller, there appears no significant rotation or even, the rotation is clearly to an unexpected direction for negative IMF $$B_y$$ B y , compared to positive IMF $$B_y$$ B y . Comparison to a model by Tsyganenko et al. (2015, doi:10.5194/angeo-33-1-2015) suggests that this asymmetry in the neutral sheet rotation between positive and negative IMF $$B_y$$ B y conditions is too large to be explained only by the currently known factors. The possible cause of the asymmetry remains unclear.

The near-Earth cross-tail current sheet: Detailed ISEE 1 and 2 case studies

1986 ◽  
Vol 91 (A4) ◽  
pp. 4287 ◽  
Author(s):  
D. J. McComas ◽  
C. T. Russell ◽  
R. C. Elphic ◽  
S. J. Bame
Keyword(s):  
Current Sheet ◽  
Case Studies ◽  
Tail Current

The Geosynchronous Substorm

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).

scholarly journals Global properties of magnetotail current sheet flapping: THEMIS perspectives

2009 ◽  
Vol 27 (1) ◽  
pp. 319-328 ◽  
Author(s):  
A. Runov ◽  
V. Angelopoulos ◽  
V. A. Sergeev ◽  
K.-H. Glassmeier ◽  
U. Auster ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Current Sheet ◽  
Growth Phase ◽  
Timing Analysis ◽  
Wave Length ◽  
Global Properties ◽  
The Cross ◽  
Magnetic Field Variations ◽  
The Magnetic Field ◽  
Magnetotail Current Sheet

Abstract. A sequence of magnetic field oscillations with an amplitude of up to 30 nT and a time scale of 30 min was detected by four of the five THEMIS spacecraft in the magnetotail plasma sheet. The probes P1 and P2 were at X=−15.2 and −12.7 RE and P3 and P4 were at X=−7.9 RE. All four probes were at −6.5>Y>−7.5 RE (major conjunction). Multi-point timing analysis of the magnetic field variations shows that fronts of the oscillations propagated flankward (dawnward and Earthward) nearly perpendicular to the direction of the magnetic maximum variation (B1) at velocities of 20–30 km/s. These are typical characteristics of current sheet flapping motion. The observed anti-correlation between ∂B1/∂t and the Z-component of the bulk velocity make it possible to estimate a flapping amplitude of 1 to 3 RE. The cross-tail scale wave-length was found to be about 5 RE. Thus the flapping waves are steep tail-aligned structures with a lengthwise scale of >10 RE. The intermittent plasma motion with the cross-tail velocity component changing its sign, observed during flapping, indicates that the flapping waves were propagating through the ambient plasma. Simultaneous observations of the magnetic field variations by THEMIS ground-based magnetometers show that the flapping oscillations were observed during the growth phase of a substorm.

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