Wednesday

All plasma processes are associated with characteristic length and time scales. The characteristic length scales in the solar wind in the inner heliosphere cover about twelve orders of magnitude between the Debye length in the corona and the size of the system (1 au). The characteristic time scales cover about ten orders of magnitude between the period of plasma oscillations near the Sun and the expansion time in the inner heliosphere. This wide range of scales is a major challenge for the numerical treatment of the solar wind, although interactions between the different scales are the very important building blocks of space-plasma physics.

We will review the most relevant multi-scale effects in space plasmas like the solar wind. These effects are a consequence of couplings between kinetic small-scale effects and the global evolution of the plasma dynamics and thermodynamics. In order to understand the behaviour of the solar wind, data from missions such as Parker Solar Probe and Solar Orbiter will connect these multi-scale effects and thus revolutionise our understanding of the processes that govern the physics of space plasmas. Our review addresses the ingredients for this multi-scale understanding of the solar wind including, for example, the role of expansion, collisions, waves/turbulence, and kinetic instabilities.