Substorms Observed by Balloon­borne Instruments, Geostationary Particle Detectors, and the VIKING UV Imager: Relativistic Dayside Electron Precipitation
G. Parks, T. Freeman, M. McCarthy, and S. Werden (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)

A substorm that occurred on July 26, 1986 produced intense dayside (near local noon) energetic electron precipitation. This precipitation event was observed by a balloon­borne X­ray pinhole camera. This event included about eight impulsive bursts that occurred every seven minutes. A similar period was observed in ground­based magnetic variations. The X­ray camera showed that these bursts filled the field of view of the camera, indicating that the precipitation region was >100 km. These events included very energetic X­rays (>100 keV) suggesting that the parent electrons responsible for the X­rays may have been relativistic. The UV imager on VIKING indicated that the balloon was located to the south of the equatorward boundary of the auroral oval. This event and previously observed events indicate that relativistic precipitation on the dayside occurs frequently in subauroral regions. A movie of this X­ray event will be shown.

10:35 UT
X­ray flux

[X-ray image]

movie: 10:19 - 10:55 UT

(animated GIF file, 409 k)

| Large­scale features | Pulsating aurora | Auroral X­ray imaging |