The Electron Temperature and Anisotropy in the Solar Wind. Comparison of the Core and Halo Populations

Pierrard, Viviane;Lazar, M.;Poedts, S.;Štverák, Š.;Trávníček, P. M.;et.al.
(2016) Solar Physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics — Vol. 291, n° 7, p. 2165-2179 (2016)

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Authors
  • Pierrard, Vivianeorcid-logoUCLouvain
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  • Lazar, M.
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  • Poedts, S.
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  • Štverák, Š.
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  • Trávníček, P. M.
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Abstract
Estimating the temperature of solar wind particles and their anisotropies is particularly important for understanding the origin of their deviations from thermal equilibrium and the effects this has. In the absence of energetic events, the velocity distribution of electrons reveals a dual structure with a thermal (Maxwellian) core and a suprathermal (kappa) halo. This article presents a detailed observational analysis of these two components, providing estimations of their temperatures and temperature anisotropies, and decoding any potential interdependence that their properties may indicate. The dataset used in this study includes more than 120 000 of the distributions measured by three missions in the ecliptic within an extended range of heliocentric distances from 0.3 to over 4 AU. The core temperature is found to decrease with the radial distance, while the halo temperature slightly increases, clarifying an apparent contradiction in previous observational analyses and providing valuable clues about the temperature of the kappa-distributed populations. For low values of the power-index kappa, these two components manifest a clear tendency to deviate from isotropy in the same direction, which seems to confirm the existence of mechanisms with similar effects on both components
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Pierrard, V., Lazar, M., Poedts, S., Štverák, Š., Maksimovic, M., & Trávníček, P. M. (2016). The Electron Temperature and Anisotropy in the Solar Wind. Comparison of the Core and Halo Populations. Solar Physics : a journal for solar and solar-stellar research and the study of solar terrestrial physics, 291(7), 2165-2179. https://doi.org/10.1007/s11207-016-0961-7 (Original work published 2016)