부산대학교 도서관

The time of arrival at ATS 6 of substorm-associated energetic (>27 keV) proton flux enhancements has been examined as a function of both energy and pitch angle by using data from the University of Minnesota electron-proton spectrometer. The protons exhibit energy dispersion with the particles with the highest energy arriving first. This energy dispersion generally has been interpreted as evidence that these particles have gradient- and curvature-drifted to the spacecraft from an acceleration region on the nightside. In the evening quadrant, proton enhancements at 90/sup 0/ pitch angle arrived at the spacecraft prior to those at small pitch angles, as would be expected for particles drifting in a dipolelike magnetic field. However, on the dayside the increase occurs first at the smallest pitch angle (approx.30/sup 0/). The difference between the arrival times of the 30/sup 0/ and 90/sup 0/ protons increases for more westward local times. For the highest energy range observed (120--377 keV), drifting protons are rarely seen at large pitch angles. These observations place severe restrictions on the simple drift models. Since the pitch angle dependence of the particle drift velocity is a field geometric quantity, the observations require the modification of present magnetospheric magnetic field models. In particular, the models need to reproduce better the enhanced field observed on the dayside near synchronous orbit. The particle energy and pitch angle dispersion observations may provide a sensitive test of future models.