Spacecraft radial alignments for investigations of the evolution of solar wind turbulence: A review

Abstract

With the launch of the Parker Solar Probe, BepiColombo, and Solar Orbiter missions in the three-year period 2018−2020, the investigation of the evolution of solar wind turbulence, dynamics, and structures in the inner heliosphere has become more readily feasible, thanks to the increasing availability of orbital configurations suitable for multi-point observations of the Sun and the processes it drives in interplanetary space. Specifically, data analysis, models, and numerical simulations based on multi-spacecraft coordinated studies have been allowing scientists to address still unsolved questions, such as how turbulence and plasma heating evolve with the heliocentric distance. A few instances of spacecraft radial alignments have been used, even before the advent of the three most recent heliospheric missions, to track the evolution of the solar wind plasma throughout interplanetary space, leading to major advances in understanding the mechanisms underlying magnetohydrodynamic turbulence and the physical processes involved in dissipating the energy transferred along the turbulent cascade to heat the plasma. This paper aims to review the different works carried out so far on these issues, describing the diagnostics adopted and discussing the most important achievements in the field of solar wind turbulence evolution.