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Journal of Geophysical Research: Space Physics

The great solar energetic particle events of 1989 observed from geosynchronous orbit

Authors

  • G. D. Reeves,

  • T. E. Cayton,

  • S. P. Gary,

  • R. D. Belian


Abstract

Los Alamos energetic proton instruments at geosynchronous orbit observed more major solar energetic particle events during 1989 than any other year since this series of detectors began observations in 1976. The temporal flux profiles of four intervals, which contain six distinct events, are compared illustrating the uniqueness of each event. Characteristic risetime and decay time are computed for each event. During two of these events, brief order-of-magnitude increases of the proton flux are observed. They are associated with sudden commencement events and dramatic changes in the solar wind. We conclude that these two brief events are likely the result of shock acceleration in the solar wind. We have fit the measured count rates to a spectral form which is exponential in rigidity, and we have examined the changes in spectral slope with time for each of the four intervals. In general, harder spectra are measured near the onset of an event followed by a softening of the spectrum as the fluxes decay. We have also investigated the effects of these events on geomagnetic activity by comparing the fluxes of >30-keV electrons at geosynchronous orbit and Kp geomagnetic index during the early part of two of the solar energetic particle events.

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