Dependence of the decay phase of solar energetic electron events on the large- scale IMF structure: ACE observations

Abstract

Using recent measurements of energetic electrons (≥38 keV) by the ACE/EPAM experiment, we examine the dependence of the characteristic decay time of two impulsive solar electron events on the large-scale structure of the Interplanetary Magnetic Field (IMF) within which the electrons are emitted. The technique of mapping the solar wind and extrapolating the frozen-in magnetic field is used to obtain the large-scale IMF structure within and beyond the location of the ACE spacecraft. We find that the electron event that occurred within a converging IMF structure exhibits a remarkably longer decay phase compared to the electron event observed inside a diverging IMF configuration. The observations provide strong evidence for the location of magnetic "barriers" in space beyond 1 AU and their role in determining the decay phase of solar energetic electron events and the establishment and maintenance of particle reservoirs in the heliosphere. Copyright 2003 by the American Geophysical Union.