Evidence of Two Active Reconnection Sites in the Distant Magnetotail

Hoshino, Masahiro; Mukai, T.; Nishida, A.; Saito, Y.; Yamamoto, T.; Kokubun, S.

doi:10.5636/jgg.48.515

Cited by 26 publications

(7 citation statements)

References 16 publications

(20 reference statements)

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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. An event as shown in Panel A of Fig.…”

Section: Discussionmentioning

confidence: 65%

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: 65%

Structure and Kinetic Properties of Plasmoids and Their Boundary Regions

Mukai

Fujimoto

Hoshino

et al. 1996

J. geomagn. geoelec

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“…At the #S2 onset time on 4 September 1999, the auroral intensity in the 557.7 nm emissions at Gillam suddenly appeared at higher latitude and became stronger than those at lower latitudes that gradually declined after the #S1 onset of the second substorm (see Figure 2). 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.…”

Section: Discussionmentioning

confidence: 78%

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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“…We interpret Event 1 as a flux rope, embedded in between the near‐Earth neutral line (NENL) and the distant neutral line. This configuration of two connected reconnection lines is sometimes referred to as an “O‐line” [e.g., Hoshino et al , 1996], since it naturally forms an O‐type neutral line in between the two reconnection sites in a two‐dimensional configuration. The flow reversal at ∼17:19 UT serves as the main argument for the passage of an O‐line.…”

Section: Passage Of An O‐line (Event 1)mentioning

confidence: 99%

On the formation of tilted flux ropes in the Earth's magnetotail observed with ARTEMIS

et al. 2012

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[1] On 21 October 2010, ARTEMIS spacecraft P2, located at about À57 R E GSM in the Earth's magnetotail, observed a series of flux ropes during the course of a moderate substorm. Subsequently, ARTEMIS spacecraft P1, located about 20 R E farther downtail and farther into the lobe than P2, observed a series of TCRs, consistent with the flux ropes observed by P2. The dual-spacecraft configuration allows simultaneous examination of these phenomena, which are interpreted as an O-line, followed by a series of flux ropes/TCRs. An inter-spacecraft time of flight analysis, assuming tailward propagation of cross-tail aligned ropes, suggests propagation speeds of up to $2000 km/s. A principal axis investigation, however, indicates that the flux ropes were tilted between 41 and 45 in the GSM x-y-plane with respect to the noon-midnight meridional plane. Taking this into account, the tailward propagation speed of the different flux ropes is determined to be between 900 and 1400 km/s. The same timing analysis also reveals that the flux rope velocity increased progressively from one flux rope to the next. A clear correlation between the magnetic field and plasma flow components inside the flux ropes was observed. As possible mechanisms leading to the formation of tilted flux ropes we suggest (a) a progressive spreading of the reconnection line along the east-west direction, leading to a boomerang-like shape and (b) a tilting of flux ropes during their formation by non-uniform reconnection with open field lines at the ends of the flux ropes. The progressive increase in the propagation velocity from the first to the last flux rope may be evidence of impulsive reconnection: initially deep inside the plasma sheet the reconnection rate is slow but as reconnection proceeds at the plasma sheet boundary and possibly lobes, the reconnection rate increases.

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Evidence of Two Active Reconnection Sites in the Distant Magnetotail

Cited by 26 publications

References 16 publications

Structure and Kinetic Properties of Plasmoids and Their Boundary Regions

Structure and Kinetic Properties of Plasmoids and Their Boundary Regions

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

On the formation of tilted flux ropes in the Earth's magnetotail observed with ARTEMIS

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