We review the main advantages and limitations of the kinetic exospheric and fluid models of the solar wind (SW). We discuss the hydrostatic model imagined by Chapman, the first supersonic hydrodynamic models published by Parker and the first generation subsonic kinetic model proposed by Chamberlain. It is shown that a correct estimation of the electric field as in the second generation kinetic exospheric models developed by Lemaire and Scherer, provides a supersonic expansion of the corona, reconciling the hydrodynamic and the kinetic approach. The third generation kinetic exospheric models considers kappa velocity distribution function (VDF) instead of a Maxwellian at the exobase and in addition they treat a non-monotonic variation of the electric potential with the radial distance; the fourth generation exospheric models include Coulomb collisions based on the Fokker--Planck collision term. Multi-fluid models of the solar wind provide a coarse grained description and reproduce with success the spatio-temporal variation of SW macroscopic properties (density, bulk velocity). The main categories of multi-fluid SW models are reviewed: the 5-moment, or Euler, models, originally proposed by Parker to describe the supersonic SW expansion; the 8-moment and 16-moment fluid models, the gyrotropic approach with improved collision terms as well as the gyrotropic models based on observed VDFs. The outstanding problem of collisions, including the long range Coulomb encounters, is also discussed, both in the kinetic and multi-fluid context. Although for decades the two approaches have been seen as opposed, in this paper we emphasize their complementary. The review of the kinetic and fluid models of the solar wind contributes also to a better evaluation of the open questions still existent in SW modeling and suggests possible future developments.
Anisotropy of Solar-Wind Turbulence in the Inner Heliosphere at Kinetic Scales: PSP Observations
太阳风湍流的各向异性是理解日球层尺度间能量传递和场与粒子间能量转换物理的关键问题。使用\emph{Parker Solar Probe}（\emph{PSP}）的测量，我们提出了一个观察的各向异性在动力学尺度上的缓慢，Alfvénic，太阳风的内日球层。\textbf{The magnetic compressibility behaves as expected for kinetic Alfvénic turbulence below the ion scale.}一个陡峭的过渡范围之间的惯性和动力学范围内的所有方向相对于当地的背景磁场方向。发现$k_\perp \gg k_\parallel$的各向异性在过渡区和动力学区都很明显，动力学区的幂次各向异性$P_\perp/P_\parallel > 10$大于过渡区的幂次各向异性，且比1 au的幂次各向异性强.光谱指数在过渡范围内从$α_{t\parallel}=-5.7\pm 1.0$到$α_{t\perp}=-3.7\pm 0.3$变化，在动力学范围内从$α_{k\parallel}=-3.12\pm 0.22$到$α_{k\perp}=-2.57\pm 0.09$变化。相应的波矢各向异性在过渡范围内具有$k_\parallel \sim k_\perp^{0.71\pm 0.17}$的标度，并且在动力学范围内变为$k_\p…
