Substorms Observed by Balloon­borne Instruments, Geostationary Particle Detectors, and the VIKING UV Imager: Large­Scale Features
S. Werden, T. Freeman, M. McCarthy, and G. Parks (Geophysics Program, AK­50, University of Washington, Seattle, WA 98195)

R. Elphinstone and J. S. Murphree (University of Calgary, Calgary, Alberta, Canada)

J. Ducarteron and J. P. Treilhou (C. E. S. R., Toulouse, France)

Two substorm associated electron precipitation events that occurred on July 26 and 27, 1986 were observed by a balloon, flown from Kiruna, Sweden, carrying an X­ray pinhole camera and a magnetometer, particle detectors in geostationary orbit, and the UV imager on the VIKING spacecraft. The first event occurred near local midnight during the expansion phase. This event included two distinct populations of electrons with different spatial and energy spectral characteristics. These observations suggest that substoms involve a two step process. The second event occurred on the dayside at subauroral latitudes to the south of the equatorward boundary of the auroral oval. Precipitation on the dayside included relativistic electrons. The spatial and energy spectral features do not exhibit behavior that can be directly correlated to events on the night side. Instead the data suggest that the dayside precipitation comes from a different source.

23:39 UT
X­ray flux


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| Pulsating aurora | Relativistic dayside electron precipitation | Auroral X­ray imaging |