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

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• 作者：V. Pierrard ; M. Lazar ; S. Poedts ; Š. Štverák ; M. Maksimovic…
• 关键词：Solar wind ; Electron velocity distributions ; Temperature anisotropy
• 刊名：Solar Physics
• 出版年：2016
• 出版时间：August 2016
• 年：2016
• 卷：291
• 期：7
• 页码：2165-2179
• 全文大小：2,178 KB
• 刊物类别：Physics and Astronomy
• 刊物主题：Physics
  Astronomy
  Extraterrestrial Physics and Space Sciences
  Astrophysics
  
• 出版者：Springer Netherlands
• ISSN：1573-093X
• 卷排序：291

文摘

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, e.g., the solar wind expansion, or the particle heating by the fluctuations. However, the existence of plasma states with anticorrelated anisotropies of the core and halo populations and the increase in their number for high values of the power-index kappa suggest a dynamic interplay of these components, mediated, most probably, by the anisotropy-driven instabilities.