Electron distributions upstream and downstream of ICME driven IP shocks

Abstract

We study suprathermal electron distributions (E > 80 eV) in regions adjacent to interplanetary (IP) shocks driven by interplanetary coronal mass ejections (ICMEs). The shocks were observed by the two STEREO spacecraft during the years 2007-2010, hence during the minimum and at the beginning of the rising phase of the current solar cycle. All the ICMEs were isolated events, meaning that the shocks were produced only due to interactions of the ICMEs with the solar wind. We find that suprathermal electron pitch angle distributions (PADs) in regions adjacent to ICME driven IP shocks vary from shock to shock. At some shocks, these electrons show the "usual" isotropic halo and a narrow, field-aligned strahl. The PADs upstream and downstream of these shocks differ only in the width of the strahl, with the later being wider in the downstream regions. In other cases we observe unusual downstream conical distributions at intermediate angles (between 0 and 90 or 90 and 180° PA), counterstreaming electrons at the shock transitions and downstream PADs without the strahl component. Here we present two shocks from our sample with such unusual electrons distributions, not reported in the literature.