Scattering of suprathermal electrons in the solar wind: ACE observations

Abstract

Suprathermal electrons in the solar wind have a strahl component with anisotropic velocity distributions which are directed along the background magnetic field away from the Sun. Analyses of strahl distributions from 73.3 eV to 987 eV as measured during the year 2004 by the SWEPAM plasma instrument on the ACE spacecraft are reported here. This manuscript describes 29 events which correspond to times of strahl pitch-angle distributions which are broader than those observed at earlier or later times and enhanced magnetic field fluctuations at frequencies ≲3 Hz. Although most previously reported observations at energies up to a few hundred eV show that strahl pitch-angle widths decrease with increasing energy, during the 29 events reported here, this width increased on average as strahl energy increased. This manuscript also develops the hypothesis that this characteristic is due to electron scattering by broadband whistler fluctuations. Copyright 2007 by the American Geophysical Union.