Solar Wind Electron Strahls Associated with a High-Latitude CME: Ulysses Observations |
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Authors: | M Lazar J Pomoell S Poedts C Dumitrache N A Popescu |
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Institution: | 1. Center for Plasma Astrophysics, K.U. Leuven, Celestijnenlaan 200B, 3001, Leuven, Belgium 2. Institut für Theoretische Physik, Lehrstuhl IV: Weltraum- und Astrophysik, Ruhr-Universit?t Bochum, 44780, Bochum, Germany 3. Astronomical Institute of Romanian Academy, 040557, Bucharest, Romania
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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 investigation of a high-latitude CME registered by the Ulysses spacecraft on 18?–?19 January 2002 (Dumitrache, Popescu, and Oncica, Solar Phys. 272, 137, 2011), by surveying the solar-wind electron distributions associated with this event. The temporal evolution of the pitch-angle distributions reveals populations of electrons that are distinguishable through their anisotropy, with clear signatures of i) electron strahls, ii) counter-streaming in the magnetic clouds and their precursors, and iii) unidirectionality 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 embedded in the CME and to refine the borders of the event. Identifying such strahls in CMEs, which preserve properties of the low β <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. |
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