Simultaneous observations of earthward flow bursts and plasmoid ejection during magnetospheric substorms

Abstract

[1] Examination of observations taken by radially aligned International Solar Terrestrial Physics spacecraft in the nightside magnetosphere on 9 July 1997 has revealed close temporal correlations between earthward flow bursts in the plasma sheet and the ejection of plasmoids. A onedimensional model of plasma sheet flow is applied to these observations to determine the time and location for the initiation of lobe flux tube reconnection. For the single clear flow burst-plasmoid pair observed during the first substorm and the three pairs produced by the second substorm, lobe flux reconnection was inferred to have started at X $ À15 to À18 R E , respectively, about 2 -5 min prior to the observations of substorm expansion phase onset. These time delays and propagation speeds are shown to be consistent with the measured plasma sheet bulk flow speeds. Substorm expansion phase onset was essentially coincident with the arrival of the flow bursts at Geotail, which was located near the inner edge of the plasma sheet at X $ À9 R E . The dipolarization of the magnetic field at geosynchronous orbit, auroral kilometric radiation (AKR) emissions, Pi2 pulsations, high-latitude negative magnetic bays, and auroral breakup marking substorm expansion onset are all coincident within the ±1 min resolution of the measurements. Accordingly, it appears that earthward of the inner edge of the plasma sheet, where Geotail was located, substorm effects propagated at speeds comparable to the Alfven speed characteristic of the high-latitude inner magnetosphere, $10 3 km s À1 . In summary, the results of our investigation strongly support the modern near-Earth neutral line (NENL) model of substorms in which the onset of lobe flux tube reconnection in the near tail is followed $2-5 min later by the braking of earthward flow bursts as they encounter the inner magnetosphere and within $1 min, by Pi2s generations, current wedge development, and AKR and auroral expansion, and finally, $10 -20 min later, by the tailward retreat of the neutral line and either the development of a new NENL or the initiation of the recovery phase.

Statistical and superposed epoch study of dipolarization events using data from Wind perigee passes

“…Auroral kilometric radiation (AKR) is widely accepted as one indicator of auroral activity and substorms (e.g. Slavin et al, 2002). We decided to examine AKR observations from the Wind WAVES instrument during the Wind dipolarization events, since this is the one substorm indicator that was guaranteed to be available during all of the dipolarization events.…”

“…The signatures observed by satellites in various regions of the night-side magnetosphere during a typical substorm include bursts of high-speed earthward and tailward plasma flow, magnetic field dipolarizations, lowfrequency fluctuations of the electric and magnetic fields, the ejection of plasmoids, and energetic particle injections at geosynchronous orbit (e.g. Slavin et al, 2002;Nagai, 1982). Recent theories have suggested that the observations of dipolarizations and earthward flows in the magnetotail may be related to the formation of the substorm current wedge and the generation of the Pi2 pulsations observed by geosynchronous satellites and ground magnetometer stations (Shiokawa et al, 1998;Kivelson, 1999, 2001).…”

MESSENGER: Exploring Mercury’s Magnetosphere

“…The reconnection process produces a magnetically confined structure (ie., looplike or helical magnetic topology) termed a "plasmoid" (Hones et al, 1984) that is ejected down the tail at high speed, as schematically depicted in Figure 7. As at the Earth, the observation of plasmoids in Mercury's magnetotail would provide direct information regarding the time of onset and intensity of magnetic reconnection (e.g., Baker et al, 1987;Slavin et al, 2002).…”

What Controls the Structure and Dynamics of Earth’s Magnetosphere?

“…This is a plasmoid, which is bounded by magnetic tension of the surrounding closed field lines connected at both ends to the Earth. Eventually, reconnection begins to process open field lines, at which point the plasmoid is released and can move downtail (Hones 1977;Baker et al 1996;Slavin et al 1999Slavin et al , 2002. In reality, if the reconnecting fields are not perfectly anti-parallel, then the plasmoid will in fact be a flux rope.…”