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Kinetic Instabilities and Turbulence in the Solar Wind
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  • Simon Opie,
  • Daniel Verscharen,
  • Christopher Chen,
  • Christopher Owen
Simon Opie
University College London

Corresponding Author:simon.opie.18@ucl.ac.uk

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Daniel Verscharen
University of New Hampshire Main Campus
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Christopher Chen
Queen Mary University of London
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Christopher Owen
University College London, Mullard Space Science Laboratory
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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.