ANGEO Annales Geophysicae ANGEO Ann. Geophys. 1432-0576 Copernicus Publications Göttingen, Germany 10.5194/angeo-20-445-2002 Energetic particle observations at the subsolar magnetopause Eccles A. A. 1 2 Fritz T. A. 1 Boston University Center for Space Physics, Boston MA, USA Correspondence to: T. A. Fritz (fritz@bu.edu) 30 04 2002 20 4 445 460 Copyright: © 2002 A. A. Eccles 2002 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://angeo.copernicus.org/articles/20/445/2002/angeo-20-445-2002.html The full text article is available as a PDF file from https://angeo.copernicus.org/articles/20/445/2002/angeo-20-445-2002.pdf

The pitch-angle distributions (PAD) of energetic particles are examined as the ISEE-1 satellite crosses the Earth’s magnetopause near the subsolar point. The investigation focuses on the possible existence of a particular type of distribution that would be associated with a source of energetic particles in the high-latitude magnetosphere. PADs, demonstrating broad, persistent field-aligned fluxes filling a single hemisphere (upper/northern or lower/southern), were observed just sunward of the magnetopause current layer for an extended period of many minutes. These distributions are a direct prediction of a possible source of energetic particles located in the high altitude dayside cusp and we present five examples in detail of the three-dimensional particle distributions to demonstrate their existence. From these results, other possible causes of such PADs are examined.<br><br><b>Key words.</b> Magnetospheric physics (energetic particles, precipitating; magnetopause, cusp and boundary layers; magnetospheric configuration and dynamics)