Large Scale Dynamics of the Magnetospheric Tail Induced by Substorms: A Multisatellite Study

Abstract

The large scale dynamics ofthe tail during substorms are examinedusing multi-satellite measurements made between 18 and 22:00 UT on August 22, 1983. We use data from ISEEI/2, 1977-007, IMP-8, and ISEE-3 located in the solar wind or tail at distances along the Sun-Earth line ranging from +11 to -205RE. During the period studied, which corresponded to a southward directed IMF, successive plasma injections were detected at 6.6RE first during a general increase of the magnetic field in the lobe. The magnetic field increase is attributed to an enhanced reconnection rate, as evidenced by the close relationship between the tail lobe magnetic energy density and the available Poynting energy in the solar wind, for near constant solar wind pressure. A Traveling Compression Region (flux rope) was detected in close association with the first energetic particle injection at geostationary orbit. After the first injections, the series of injections continued and the last ones are shown to be linked with a tailward propagating cross-tail current disruption detected onboard IMP-8 at --35RE. This event is seen in the distant tail at 205RE onboard ISEE-3 as an increase of the tail radius; the far magnetosphere engulfed the ISEE-3 satellite which was located in the solar wind prior to the event. The characteristic time delay between cross-tail current disruption onset occurring in the near-Earth plasma sheet and the enhancement of the tail diameter at 205RE is on the order of 40 minutes. Several hours before this event, a similar case was detected in which partial cross-tail current disruption in the mid-tail was also related to a far tail expansion. In both cases, the observed signatures are in agreement with the concept of the ejection of plasmoids from the magnetospheric tail with velocities comparable to that of the solarwind. These results strongly suggest that traveling cross-tail current disruption and plasmoid ejection from the far tail are the signature of the same propagating plasma process.

Far tail (255RE) fast response to very weak magnetic activity

“…These boundary motions can hardly be related to a plasmoid as a widening of the tail is expected from such a high‐pressure structure. Previous work has indeed shown, as expected, that plasmoids lead a satellite located in the distant magnetosheath to pass inside the lobe [e.g., Sauvaud et al , 1996], i.e., the reverse motion of what is observed for the cases presented here.…”

“…Magnetopause motions in the far tail have already been shown to be induced by substorm associated processes: a study performed from simultaneous IMP‐8 and ISEE‐3 data by Sauvaud et al [1996] has shown a characteristic time delay of 40 min between cross‐tail current disruption onset occurring in the near‐Earth plasma sheet and the enhancement of the tail diameter at 205 R E . The observed signatures were in agreement with the concept of the ejection of plasmoids from the magnetospheric tail and the tailward propagation of a compression region with enhanced pressure, so that the ISEE‐3 satellite initially in the distant magnetosheath was entering the magnetosphere when the high‐pressure region reached its location.…”

“…Direct comparisons of IMP‐8 midtail measurements of the cross tail current disruption and of distant effects induced by the passage of a plasmoid in the far tail onboard ISEE‐3 have also been reported [ Sauvaud et al , 1996]. Observations of plasmoids are in fact highly correlated with substorm onsets in view of magnetic field data observed at ground stations and energetic particle data from geosynchronous satellites [ Moldwin and Hughes , 1993; Nagai et al , 1994].…”

Sporadic plasma sheet ion injections into the high‐altitude auroral bulge: Satellite observations

“…Assessing the large-scale dynamics of the magnetospheric system during substorms has motivated a number of studies in the recent years, and it is still one of the main areas of magnetospheric research. Magnetic field observations in the equatorial region of the inner magnetosphere and farther in the magnetotail lobe have shown that a reconfiguration of the magnetic field topology ("dipolarization") linked to a partial disruption of the near-Earth cross-tail current is associated with substorm onsets detected as breakups of auroral forms in the ionosphere [e.g., Sauvaud and Winckler, 1980;Lui, 1988, as the plasma sheet recovery (thickening) and the release of plasmoids from the far tail [e.g., Hones et al, 1967Hones et al, , 1984Scholer et al, 1984;Sauvaud et al, 1996;Nagai et al, 1997Nagai et al, , 1998].…”

A study of the changes of the near‐Earth plasma sheet and lobe driven by multiple substorms: Comparison with a full particle simulation of reconnection

“…By fitting the data with a simple disrupted current slab whose tailward boundary propagates tailward, as well as using multipoint measurements (ISEE, IMP‐8 and INTERBALL‐Tail), it was concluded that the CD started at 6–9 R E and propagated down the tail with a velocity of the order of 150–350 km/s over tens of R E during substorm expansion phases [ Jacquey et al , 1991, 1993, 1998; Ohtani et al , 1992; Jacquey and Sauvaud , 1994]. Furthermore, direct comparisons of IMP‐8 and ISEE‐3 data during a major substorm led to linking CD and plasmoids ejected from the tail at ≈20 R E , and observed in the far tail during a major disruption [ Sauvaud et al , 1996a, 1996b].…”