Multiple-satellite studies of magnetospheric substorms: Distinction between polar magnetic substorms and convection-driven negative bays
It is generally believed that long intervals of intense (500-1000 ..gamma..) negative auroral zone bays are caused by magnetospheric substorm occurrences at a high repetition rate. Since individual substorm phases may then overlap in time and occur within limited local time sectors, it may be difficult to identify their characteristic signatures. In this paper we have examined ground and multiple-satellite recordings during an approx.5-hour interval of persistent auroral zone activity in a systematic search for substorm expansion signatures. It appears that this enduring activity started as a rather weak substorm which thereafter developed into strong magnetospheric activity driven by a continuously southward interplanetary magnetic field (IMF). During this period there were no clear mid-latitude positive bays, and pulsation recordings from different local time sectors showed only one instance of weak Pi 2-like variations. The associated high-latitude equivalent ionospheric current pattern is consistent with a convection system, and we refer to this activity as the convection bay. Following the plasma sheet and ground signatures of substorm recovery early in the convection bay, there was no definite indication of substorm expansions other than this weak magnetic pulsation in any recordings during the next approx.3-1/2 hours until a clear substorm emerged. This substorm onset, which was associated with a not particularly strong auroral zone bay, was accompanied by the full complement of substorm expansion signatures. At this time a minimum plasma sheet thickness of only a few tenths of an earth radius was observed in the region where a neutral line appears to form during substorms. Prior to this onset, the plasma sheet was relatively thick, and it seems that the neutral line was located well tailward of the Vela orbit (rapprox.18 R/sub E/).
- Research Organization:
- Institute of Geophysics and Planetary Physics, University of California, Los Angeles, California 90024
- OSTI ID:
- 5034586
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 83:A2
- Country of Publication:
- United States
- Language:
- English
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Multiple-satellite studies of magnetospheric substorms: plasma sheet recovery and the poleward leap of auroral zone activity
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