Solar Wind Plasma Particles Organized by the Flow Speed
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Solar Wind Plasma Particles Organized by the Flow Speed Viviane Pierrard1,2 Stepan Štverák5,6
· Marian Lazar3,4
·
Received: 2 September 2020 / Accepted: 27 October 2020 © The Author(s) 2020
Abstract Recent reports of the first data from Parker Solar Probe (PSP) have pointed to a series of links, correlations or anti-correlations between the solar wind bulk speed (VSW ) and physical properties of plasma particles from less than 0.25 AU in the corona. In the present paper, we describe corresponding and additional links of solar wind properties, at 0.4 AU and 1.0 AU, in an attempt to complement the PSP data and understand their evolution. A detailed analysis is carried out for the main electron populations, comparing the low-energy (thermal) core and the collisionless suprathermal halo. We show that the anti-correlation observed at 0.4 AU between VSW and the number density (average value) is maintained also at 1 AU for both the core and halo electrons. On the contrary, only the core electrons manifest a clear anti-correlation of the temperature with VSW , while the halo temperature does not vary much. We also describe the ions, protons and helium, which have a more reduced mobility and their properties exhibit different variations with the solar wind speed. The results are used to shed more light on the mechanisms leading to a differential acceleration of these species and the origin of slow and fast wind modulation. Keywords Solar wind · Electrons · Protons · Observations
B V. Pierrard
[email protected]
1
Royal Belgian Institute for Space Aeronomy BIRA-IASB, Space Physics and STCE, 3 av. Circulaire, 1180 Brussels, Belgium
2
Center for Space Radiations (CSR), Georges Lemaître Centre for Earth and Climate Research (TECLIM), Earth and Life Institute (ELI), Université Catholique de Louvain (UCLouvain), Place Louis Pasteur 3 bte L4.03.08, 1348 Louvain-La-Neuve, Belgium
3
Theoretical Physics IV, Ruhr-University Bochum, 44780 Bochum, Germany
4
Centre for Mathematical Plasma Astrophysics, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
5
Institute of Atmospheric Physics, Czech Academy of Sciences, Prague, Czech Republic
6
Astronomical Institute, Czech Academy of Sciences, Ondrejov, Czech Republic
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1. Introduction Properties of the solar wind (SW) plasma particles have been measured in-situ by a multitude of spacecraft missions, e.g., Ulysses, Helios 1 and 2, Wind, Cluster, etc. (Domingo, 2002; Meyer-Vernet, 2007; Lazar, 2012), enabling also indirect interpretations of plasma physics at low heliocentric distances in the corona where direct in-situ measurements were not possible (Scudder, 1992; Pierrard, Maksimovic, and Lemaire, 2001a,b). The new observations from Parker Solar Probe (PSP) and Solar Orbiter (SO) are expected to confirm these predictions, and explain the main mechanisms which trigger plasma outflows and modulate the main properties of the SW plasma particles, i.e., electrons, protons and heavier ions (Berˇciˇc et al., 2020; Halekas et al
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