The multi-scale nature of the solar wind

Daniel Verscharen; Kristopher G Klein; Bennett A Maruca

doi:10.1007/s41116-019-0021-0

The multi-scale nature of the solar wind

Living Rev Sol Phys. 2019;16(1):5. doi: 10.1007/s41116-019-0021-0. Epub 2019 Dec 9.

Authors

Daniel Verscharen^{1

2}, Kristopher G Klein³, Bennett A Maruca⁴

Affiliations

¹ 1Mullard Space Science Laboratory, University College London, Dorking, RH5 6NT UK.
² 2Space Science Center, University of New Hampshire, Durham, NH 03824 USA.
³ 3Lunar and Planetary Laboratory and Department of Planetary Sciences, University of Arizona, Tucson, AZ 85719 USA.
⁴ 4Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 USA.

Abstract

The solar wind is a magnetized plasma and as such exhibits collective plasma behavior associated with its characteristic spatial and temporal scales. The characteristic length scales include the size of the heliosphere, the collisional mean free paths of all species, their inertial lengths, their gyration radii, and their Debye lengths. The characteristic timescales include the expansion time, the collision times, and the periods associated with gyration, waves, and oscillations. We review the past and present research into the multi-scale nature of the solar wind based on in-situ spacecraft measurements and plasma theory. We emphasize that couplings of processes across scales are important for the global dynamics and thermodynamics of the solar wind. We describe methods to measure in-situ properties of particles and fields. We then discuss the role of expansion effects, non-equilibrium distribution functions, collisions, waves, turbulence, and kinetic microinstabilities for the multi-scale plasma evolution.

Keywords: Coulomb collisions; Kinetic instabilities; Plasma waves and turbulence; Solar wind; Spacecraft measurements.

Publication types

Review