Parker Solar Probe Observations of Turbulence in the Near-Sun Solar Wind and Solar Corona

Since its launch, Parker Solar Probe has allowed us an unprecedented opportunity to understand how solar wind turbulence works up close to the Sun, and the role that it plays in shaping the solar wind that we see. In this presentation, I will discuss what we have learnt from the most recent orbits where PSP crossed several times into sub-Alfvénic wind and saw clear changes in the turbulence properties. In particular, we see a change in the evolution of turbulence amplitudes that allow testing of the WKB vs non-WKB evolution of the fluctuations. We see a clear decrease of amplitudes in the sub-Alfvénic wind, as expected, that shows up prominently in the normalised amplitude δB/B - this is compared to theoretical predictions, allowing us to study the processes responsible for the fluctuations growing to the large amplitudes seen in the super-Alfvénic wind (δB/B~1, also known as "switchbacks"). We also discuss how other turbulence properties change in the sub-Alfvénic wind, including the magnetic compressibility, cross-helicity, and Elsasser spectra. These results will be discussed in the context of understanding the mechanisms for both the acceleration of the solar wind and the generation of large-amplitude turbulence.