Alfvénic versus non-Alfvénic turbulence in the inner heliosphere as observed by Parker Solar Probe

Abstract

We make use of the Parker Solar Probe (PSP) data to explore the nature of solar wind turbulence focusing on the Alfvénic character and power spectra of the fluctuations and their dependence on distance and context (i.e. large scale solar wind properties), aiming to understand the role that different effects such as source properties, solar wind expansion, stream interaction might play in determining the turbulent state. We carry out a statistical survey of the data from the first five orbits of PSP with a focus on how the fluctuation properties at the large, MHD scales, vary with different solar wind streams and distance from the Sun. A more in-depth analysis from several selected periods is also presented. Our results show that as fluctuations are transported outward by the solar wind, the magnetic field spectrum steepens while the shape of the velocity spectrum remains unchanged. The steepening process is controlled by the "age" of the turbulence, determined by the wind speed together with the radial distance. Statistically, faster solar wind has higher "Alfvénicity", with more dominant outward propagating wave component and more balanced magnetic/kinetic energies. The outward wave dominance gradually weakens with radial distance, while the excess of magnetic energy is found to be stronger as we move closer toward the Sun. We show that the turbulence properties can vary significantly stream to stream even if these streams are of similar speed, indicating very different origins of these streams. Especially, the slow wind that originates near the polar coronal holes has much lower Alfvénicity compared with the slow wind that originates from the active regions/pseudostreamers. We show that structures such as heliospheric current sheets and velocity shears can play an important role in modifying the properties of the turbulence.

References in corpus (7)

• The Evolution and Role of Solar Wind Turbulence in the Inner Heliosphere
• Switchbacks in the near-Sun magnetic field: long memory and impact on the turbulence cascade
• First in-situ Measurements of Electron Density and Temperature from Quasi-Thermal Noise Spectroscopy with Parker Solar Probe/FIELDS
• Magnetic field kinks and folds in the solar wind
• Cross Helicity Reversals In Magnetic Switchbacks
• Evolution of turbulence in the expanding solar wind, a numerical study
• Propagation of Alfvén waves in the expanding solar wind with the fast-slow stream interaction

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• Does Turbulence along the Coronal Current Sheet Drive Ion Cyclotron Waves?
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