A Quasi-stagnant Plasmoid Observed With Geotail on October 15, 1993

Kawano, Hideaki; Nishida, A.; Fujimoto, M.; Mukai, T.; Kokubun, S.; Yamamoto, T.; Terasawa, T.; Hirahara, Masafumi; Saito, Y.; Machida, S.; Yumoto, K.; Matsumoto, Hiroshi; Murata, Takeshi

doi:10.5636/jgg.48.525

Cited by 20 publications

(5 citation statements)

References 22 publications

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“…This two-point reconnection model has been suggested to interpret a stagnant plasmoid (Nishida et al, 1986;Kawano et al, 1996). Hoshino et al (1996) has also reported evidence for this model with the GEOTAIL observations.…”

Section: Discussionmentioning

confidence: 71%

Structure and Kinetic Properties of Plasmoids and Their Boundary Regions

Mukai

Fujimoto

Hoshino

et al. 1996

J. geomagn. geoelec

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Based on GEOTAIL/LEP observations in the distant magnetotail, this paper reports on several new features of velocity distribution functions of electrons and ions within a plasmoid and at its boundary. Here we use the term'plasmoid' in a wider meaning than usual in spite of the presence of significant magnetic By fields. In the lobe, as expected from MHD simulations of magnetic reconnection processes, cold plasmas are pushed away from the plasma sheet before the arrival of plasmoids, while after the plasmoid passage the convection is enhanced toward the normal direction to the plasma sheet. The cold ions flow into the plasmoid along magnetic field lines, are heated and accelerated perpendicularly at the boundary, and finally merge with hot plasmas deeper inside the plasmoids. Deep inside plasmoids, however, the ion distribution functions often show the existence of counterstreaming ion beams, while the simultaneously measured electron distribution functions show a flat-top distribution. It is noted that the presence of the counterstreaming ions is a fine structure along magnetic field lines inside the whole distribution convecting tailward with speeds of 500-900 km/s. The relative velocity of the two components along the magnetic field line reaches 1000-1500 km/s, which is much higher than the local Alfven speed. Each component has an anisotropic distribution with respect to its center in the velocity space; the perpendicular temperature is several times higher than the parallel temperature. We conclude that these counterstreaming ions are most likely of lobe origin, and they have not had time enough for thermalization. They might have entered the plasmoid from the northern and southern lobes, being heated and accelerated through slow-mode shocks at the boundaries. Hence, these field lines are open, and both ends are connected to the northern and southern lobes. This phenomenon is observed predominantly in the latter part of the plasmoid after southward turning of the magnetic field, especially after the plasma bulk speed has increased stepwise and the Ba/B, field magnitudes have attained the peak value. It is also observed even near the neutral sheet, where the magnetic Bs field is very small, but significant By and/or B. fields exist. Since the tailward flow speed becomes faster associated with the above phenomenon, these open field lines would be draped around the leading (core) part of plasmoids. The compression due to the draping may increase the field intensity.

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Section: Discussionmentioning

confidence: 71%

Structure and Kinetic Properties of Plasmoids and Their Boundary Regions

Mukai

Fujimoto

Hoshino

et al. 1996

J. geomagn. geoelec

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“…As pointed out by Slavin et al [1989] and Ieda et al [1998], enhancements of the total pressure and the total magnetic field cannot be seen in waves. Therefore we interpret the observed signatures as successive tailward moving small plasmoids, although they were much slower than usual plasmoids, i.e., quasi‐stagnant plasmoids [ Nishida et al , 1986; Kawano et al , 1996]. Slowly moving plasmoids at less than 200 km/s are sometimes observed in the near‐Earth tail; see the examples of Slavin et al [2003, 2005].…”

Section: Discussionmentioning

confidence: 87%

Plasmoids observed in the near‐Earth magnetotail at X ∼ −7 R_E

et al. 2005

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[1] Recent studies have statistically shown that the magnetic reconnection site at substorm expansion onset is located in the magnetotail at X $ À20 R E on average. For a substorm event that occurred at $0153 UT on 2 July 1996, however, Geotail observed a series of tailward but slow flows with southward magnetic fields fairly close to the Earth at (X, Y) $ (À7, 9) R E . The flows had enhancements of the total pressure and the total magnetic field as well as bidirectional field-aligned low-energy electrons in their central part. We interpret these as signatures for tailward moving small plasmoids with scales of $0.5-3 R E . Considering that GOES-8 observed a dipolarization at (X, Y) $ (À4, 5) R E after the expansion onset, we estimate that the magnetic reconnection occurred between the Geotail and GOES-8 positions. UVI auroral images from Polar and ground magnetic field data show that this substorm, initiated at $20 hours MLT and $64°magnetic latitude, was not very intense, and the period examined was not during an intense storm. The southward interplanetary magnetic field (IMF) was not very large, while the large duskward IMF persisted for more than 12 hours before the onset as well as the somewhat large solar wind dynamic pressure. It seems likely that the global ionospheric convection was not very strong. Locally enhanced convection and auroral oval expansion due to the large IMF B y and the solar wind dynamic pressure might lead to the initiation of the magnetic reconnection much closer to the Earth than usual.

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“…By using Geotail observations, Hoshino et al [1996] confirmed the existence of a second distant neutral point in the magnetotail. In addition, Kawano et al [1996] found the sequence of earthward and tailward field-aligned beam directions when Geotail entered a plasmoid. At the north of Gillam, the geomagnetic field lines may thread through the tail lobes over the near-Earth neutral point.…”

Section: Discussionmentioning

confidence: 99%

On the relationships between double‐onset substorm, pseudobreakup, and IMF variation: The 4 September 1999 event

et al. 2005

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[1] The relationships between double-onset substorm, pseudobreakup, and IMF variation were investigated with magnetic, auroral, and particle observations from space to the ground during 0200-0600 UT on 4 September 1999. There were five consecutive bursts of Pi2 pulsations on the ground during the time of interest. The onset time of ground Pi2s maps to the same variation sequence in the IMF structure seen propagating to the Earth in multiple satellite observations in the upstream region. The comparison of auroral and energetic particle data with IMF observations shows that a sequence of two doubleonset substorms intervened by a pseudobreakup appears in two distinct cycles of southward IMF followed by a northward interval. For the first substorm, the first onset begins when the B y magnitude declines after the IMF turns southward for about 90 min, and the second onset occurs after northward turning of the IMF accompanied by an increasing B y magnitude. The pseudobreakup appears while the IMF turns southward and the B y magnitude slightly decreases. For the second substorm, the first onset commences while the IMF remains southward with a steady B y magnitude, and the second onset occurs after the IMF becomes strongly northward and the B y magnitude decreases instead. These observations can be explained with the two-neutral-point model. The first onset occurs when the IMF turns southward. Reconnection at the near-Earth neutral point first begins on closed field lines within the plasma sheet, and the second onset occurs when the IMF turns northward and reconnection at the distant neutral point ceases and reconnection at the near-Earth neutral point may reach the open flux of the tail lobes. In addition, a decrease in the B y magnitude may help reduce magnetotail convection and release all the built-up flux to allow the onset to commence after northward turning of the IMF. If the IMF remains southward, the reduction of magnetotail convection due to a decreasing B y would lead to a pseudobreakup instead. In contrast, an increasing B y magnitude would increase magnetotail convection and weaken magnetospheric substorm after the IMF turns northward. Consequently, for the occurrence of double-onset substorms and pseudobreakups, not only the first onset begins spontaneously during steady southward IMF and the second onset appears after northward turning of the IMF but the B y change also affects magnetotail convection which may evoke (or abate) the substorm-related activation while the IMF turns southward (or northward).

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A Quasi-stagnant Plasmoid Observed With Geotail on October 15, 1993

Cited by 20 publications

References 22 publications

Structure and Kinetic Properties of Plasmoids and Their Boundary Regions

Structure and Kinetic Properties of Plasmoids and Their Boundary Regions

Plasmoids observed in the near‐Earth magnetotail at X ∼ −7 R_E

On the relationships between double‐onset substorm, pseudobreakup, and IMF variation: The 4 September 1999 event

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A Quasi-stagnant Plasmoid Observed With Geotail on October 15, 1993

Cited by 20 publications

References 22 publications

Structure and Kinetic Properties of Plasmoids and Their Boundary Regions

Structure and Kinetic Properties of Plasmoids and Their Boundary Regions

Plasmoids observed in the near‐Earth magnetotail at X ∼ −7 RE

On the relationships between double‐onset substorm, pseudobreakup, and IMF variation: The 4 September 1999 event

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Plasmoids observed in the near‐Earth magnetotail at X ∼ −7 R_E