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Observations of plasma sheet expansion at substorm onset, R = 15 to 22 R e
Author(s) -
Lyons L. R.,
Huang C. Y.
Publication year - 1992
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/92gl02108
Subject(s) - substorm , plasma sheet , physics , longitude , geophysics , magnetosphere , local time , synchronous orbit , plasma , wedge (geometry) , satellite , magnetic field , astrophysics , latitude , geodesy , geology , astronomy , optics , geosynchronous orbit , statistics , mathematics , quantum mechanics
We have used a large number of auroral magnetograms to identify four isolated substorms and estimate their onset times. At the onsets, ISEE‐1 was in the vicinity of magnetic midnight at radial distances of 15.6 to 21.8 R e and very near the outer boundary of the plasma sheet. We find that, for each event, the plasma sheet expanded, and the magnetic field dipolarized at the inferred onset time. Our most definitive event occurred while ISEE was at a geocentric radial distance of 21.8 R e . This result conflicts with previous understanding, though further verification of the result is required. Our observations show very similar characteristics to those observed at synchronous orbit, and they are consistent with an extension of a portion of the substorm current wedge to the radial distance of the satellite. If this explanation is correct, ISEE must have been within the longitude range of the substorm current wedge at the onsets.