Investigating solar wind acceleration and non-adiabatic expansion with the Parker Solar Probe and Solar Orbiter missions

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The project will focus on the inner Heliosphere and the properties of the Solar Wind plasma close to the Sun: origin and acceleration; expansion in interplanetary space. The research activity will exploit new measurements by the NASA Parker Solar Probe (PSP) mission (launched in 2018) and in the near future by Solar Orbiter (launch in February 2019) during the cruise phase. These include high-resolution in situ observations of electric and magnetic fields and particles (ions and electrons) that compose the solar wind plasma at different heliocentric distances. The project will take advantage of the fact that PSP is collecting measurements in close-Sun regions unexplored before and its closest approach will continue to gradually reduce - from ~30 Solar radii to less than 20 during the 3 years of the project. These circumstances will make possible detailed studies of the solar wind plasma thermodynamic state and its evolution with radial distance, in order to identify processes responsible for the energy exchanges between particles and fields during the expansion and ultimately leading to the heating of the plasma and the dissipation of the solar wind turbulent cascade. The methodology adopted will be mostly based on data analysis and the associated interpretative modelling. Results will be critically reviewed and compared with state-of-art theoretical and numerical predictions, exploiting both existing and new scientific collaborations of the Space Physics Group, in the UK and abroad.