Solar Wind Electron Strahls Associated with a High-Latitude CME: \emph{Ulysses} Observations

TL;DR

This study analyzes Ulysses spacecraft data to characterize electron strahls and counter-streaming beams within a high-latitude CME, providing insights into magnetic cloud structures and the origin of solar wind electrons.

Contribution

It offers detailed observations of electron distributions in a high-latitude CME, clarifying the nature of electron strahls and their relation to coronal plasma properties.

Findings

Identification of electron strahls and counter-streaming beams within the CME

Refinement of magnetic cloud boundaries based on electron data

Support for the hypothesis that electron populations are remnants of coronal electrons

Abstract

Counterstreaming beams of electrons are ubiquitous in coronal mass ejections (CMEs) - although their existence is not unanimously accepted as a necessary and/or sufficient signature of these events. We continue the investigations of a high-latitude CME registered by the \emph{Ulysses} spacecraft on January 18\,--\,19, 2002 (Dumitrache, Popescu, and Oncica, Solar Phys. {\bf 272}, 137, 2011), by surveying the solar wind electron distributions associated with this event. The temporal-evolution of the pitch-angle distributions reveal populations of electrons distinguishable through their anisotropy, with clear signatures of i) electron strahls, ii) counter-streaming in the magnetic clouds and their precursors, and iii) unidirectional in the fast wind preceding the CME. The analysis of the counter-streams inside the CME allows us to elucidate the complexity of the magnetic-cloud structures embeded in the CME and to refine the borders of the event. Identifying such strahls in CMEs, which preserve properties of the low $\beta < 1$ coronal plasma, gives more support to the hypothesis that these populations are remnants of the hot coronal electrons that escape from the electrostatic potential of the Sun into the heliosphere.