Simultaneous THEMIS observations in the near‐tail portion of the inner and outer plasma sheet flux tubes at substorm onset

Сергеев, В. А.; Apatenkov, S.; Angelopoulos, V.; McFadden, J. P.; Larson, D. E.; Bonnell, J. W.; Кузнецова, М.; Partamies, Noora; Honary, F.

doi:10.1029/2008ja013527

Cited by 17 publications

(23 citation statements)

References 25 publications

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“…The oscillations of B z in the Pi2 frequency range began at the same time that the dipolarization started. The Z component of the plasma flow during the interval (Figure 7f) was similar to that during the plasma sheet expansion on 27 December 2007 [ Sergeev et al , 2008].…”

Section: Observations From Themismentioning

confidence: 76%

THEMIS observations of the near‐Earth plasma sheet during a substorm

Tang

Angelopoulos

et al. 2009

J. Geophys. Res.

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[1] We present observations of a substorm on 13 March 2008 by Time History of Events and Macroscale Interactions during Substorms (THEMIS) spacecraft in the near-Earth tail during the plasma sheet expansion evidenced by increase in the plasma density and temperature. The main features of the event are as follows: (1) Cross-tail current reduction or current disruption (CD) was observed in the near-Earth tail at X $ À8.0 R E and Y $ 2.0 R E , marked by a sharp drop of jB x j and accompanied by sharp increases in the plasma density and temperature, manifesting a rapid expansion (recovery) of the local plasma sheet. During the course of the plasma sheet expansion, the propagation speed of the dipolarization is $48 km/s in tailward direction and $35 km/s in azimuthal direction.(2) In the inner edge of the plasma sheet, slow flux pileup is observed. The magnetic flux pileup is characterized by continuous enhancement of B z and B t and a reduction of the plasma density, pressure P th , and b in the flow-braking region. The tailward moving plasma sheet expansion (CD) is also passing across the flow-braking region. In short, the dipolarization in the inner edge of the plasma sheet can be attributed to CD, while the tailward progression of dipolarization in the flow-braking region can be attributed to magnetic flux pileup. (3) A sharp decrease in the magnitude of B x at P1 (À13.1 R E , 2.5 R E , À0.56 R E ) prior to the dipolarization at P5 is difficult to explain as part of the outward evolution of the CD. The rapid change in the magnetic field topology, and signatures of earthward flows and dipolarization observed at P1 prior to Pi2 onset may be caused by inward motion of flux from magnetic reconnection in the midtail (20-30 R E ). Tail reconnection prior to substorm expansion can result in a sudden change of the near-Earth configuration, which may result in instabilities related to the onset of CD.

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Section: Observations From Themismentioning

confidence: 76%

THEMIS observations of the near‐Earth plasma sheet during a substorm

Tang

Angelopoulos

et al. 2009

J. Geophys. Res.

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“…This small and gradual increase of B z , which itself is only a minor component of the total magnetic field at the current sheet boundary region of our interest, has little influence on the overall B ‐field topology and thus is not considered as signature of CD (see our criteria stated in section 4). Sergeev et al [2008] interpreted the concurrence of B z increase and the plasma sheet thinning as a consequence of the near‐Earth reconnection via a global MHD simulation. As mentioned above we cannot entirely exclude the possibility of the reconnection for many of our events.…”

Section: Discussionmentioning

confidence: 99%

Ion temperature drop and quasi‐electrostatic electric field at the current sheet boundary minutes prior to the local current disruption

2009

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[1] From a survey of the cross-tail current disruption (CD) events in the near-Earth plasma sheet collected from the Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, we identify a highly repeatable class of event occurring at the current sheet boundary in a few minutes before the local CD onset. Salient features of this class of event include (1) a precipitous drop of the ion temperature, (2) concurrent growth of a neutral sheet-pointing electric field, and (3) ULF wave activations at Pi1/Pi2 bands. We interpret the ion temperature drop as a manifestation of the extremely thinning of the local current sheet prior to its disruption. This thinning process is inferred as nonadiabatic by nature. Particularly, when the current sheet thickness is down to ion kinetic scales, the ions are demagnetized, and a quasi-electrostatic neutral sheet-pointing electric field emerges owing to the charge separation. The ULF fluctuations of electric/magnetic field have a two-band structure. The lower-frequency band with a period of 50 to 80 s is interpreted as an Alfvenic mode coupled from other preonset wave modes excited at the equatorial plasma sheet such as the ballooning. The higher-frequency wave at 10-to 20-s periods is attributed to some instability mode, directly leading to the disruption of the thin current sheet (TCS). We suggest that an extremely thinned non-Harris TCS and the emergence of quasi-electrostatic field constitute the conducive conditions for a local CD to occur. A companion paper by covers some theoretical aspects of this study.Citation: Liang, J., W. W. Liu, and E. F. Donovan (2009), Ion temperature drop and quasi-electrostatic electric field at the current sheet boundary minutes prior to the local current disruption,

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“…Enhanced southward flows, corresponding to the dawn-to-dusk electric field of up to 2.5 mV/m, continued afterward, accompanied by a decrease in pressure, which indicates unloading and exiting to the lobe. Such signatures have been reported as the current sheet thinning associated with the enhanced flux transport rate due to activation of near-Earth reconnection tailward of the spacecraft (Sergeev et al 2008). Therefore, Geotail was likely close to the reconnection region and then detected its tailward progression.…”

Section: Observationsmentioning

confidence: 98%

Near-Earth plasma sheet boundary dynamics during substorm dipolarization

Nakamura

Nagai

Birn

et al. 2017

Earth Planets Space

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We report on the large-scale evolution of dipolarization in the near-Earth plasma sheet during an intense (AL ~ −1000 nT) substorm on August 10, 2016, when multiple spacecraft at radial distances between 4 and 15 R E were present in the night-side magnetosphere. This global dipolarization consisted of multiple short-timescale (a couple of minutes) B z disturbances detected by spacecraft distributed over 9 MLT, consistent with the large-scale substorm current wedge observed by ground-based magnetometers. The four spacecraft of the Magnetospheric Multiscale were located in the southern hemisphere plasma sheet and observed fast flow disturbances associated with this dipolarization. The high-time-resolution measurements from MMS enable us to detect the rapid motion of the field structures and flow disturbances separately. A distinct pattern of the flow and field disturbance near the plasma boundaries was found. We suggest that a vortex motion created around the localized flows resulted in another fieldaligned current system at the off-equatorial side of the BBF-associated R1/R2 systems, as was predicted by the MHD simulation of a localized reconnection jet. The observations by GOES and Geotail, which were located in the opposite hemisphere and local time, support this view. We demonstrate that the processes of both Earthward flow braking and of accumulated magnetic flux evolving tailward also control the dynamics in the boundary region of the near-Earth plasma sheet.

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Simultaneous THEMIS observations in the near‐tail portion of the inner and outer plasma sheet flux tubes at substorm onset

Cited by 17 publications

References 25 publications

THEMIS observations of the near‐Earth plasma sheet during a substorm

THEMIS observations of the near‐Earth plasma sheet during a substorm

Ion temperature drop and quasi‐electrostatic electric field at the current sheet boundary minutes prior to the local current disruption

Near-Earth plasma sheet boundary dynamics during substorm dipolarization

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