Abstract
The solar wind is a continuous outflow of plasma from the Sun, which
expands into the space between the planets in our solar system and forms
the heliosphere. The solar wind is inherently turbulent and
characterised by kinetic micro-instabilities on a range of scales. The
Sun also intermittently ejects mass (coronal mass ejections; CMEs) or
solar energetic particles (SEPs) which change their trajectory or energy
due to their interactions with the solar wind. When these violent
particle events hit the Earth’s magnetosphere, they can cause “space
weather” with both long- and short-term impacts on our natural and
technological environment. This presentation investigates the behaviour
and the effects of kinetic instabilities in a turbulent plasma with
particular emphasis on energy transfer processes. We utilise the
unprecedented observations from ESA’s Solar Orbiter spacecraft, launched
in February 2020, to advance our understanding of the Sun, the solar
wind, and space weather. Large-scale compressions (ubiquitous in
solar-wind turbulence) create conditions for proton, alpha-particle and
electron microinstabilities, which then transfer energy to small-scale
fluctuations. These instability-driven small-scale fluctuations,
including those driven by turbulence and other sources of free energy
(e.g. particle beams, differential flows, heat fluxes, temperature
anisotropies), make a significant contribution to the fluctuation
spectrum at kinetic scales, where energy dissipation occurs. We consider
instabilities driven by turbulence in the plasma by using statistical
methods to analyse the Solar Orbiter data and characterise the
turbulence at the relevant scales and amplitude. Specifically, we
evaluate the processes by which turbulence combined with temperature
anisotropy causes instability, comparing theoretical calculations with
the high resolution data available from the Solar Orbiter MAG and SWA
instruments.