# PSP Bibliography

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Sub-Alfv\ enic Solar Wind Observed by the Parker Solar Probe: Characterization of Turbulence, Anisotropy, Intermittency, and Switchback

 Author Bandyopadhyay, R.; Matthaeus, W.~H.; McComas, D.~J.; Chhiber, R.; Usmanov, A.~V.; Huang, J.; Livi, R.; Larson, D.~E.; Kasper, J.~C.; Case, A.~W.; Stevens, M.; Whittlesey, P.; Romeo, O.~M.; Bale, S.~D.; Bonnell, J.~W.; de Wit, Dudok; Goetz, K.; Harvey, P.~R.; MacDowall, R.~J.; Malaspina, D.~M.; Pulupa, M.; Keywords Parker Data Used; 1544; 1534; 824; 23; Physics - Space Physics; Astrophysics - Solar and Stellar Astrophysics; Physics - Plasma Physics Abstract In the lower solar coronal regions where the magnetic field is dominant, the Alfv\ en speed is much higher than the wind speed. In contrast, the near-Earth solar wind is strongly super- Alfv\ enic, i.e., the wind speed greatly exceeds the Alfv\ en speed. The transition between these regimes is classically described as the Alfv\ en point but may in fact occur in a distributed Alfv\ en critical region. NASA s Parker Solar Probe (PSP) mission has entered this region, as it follows a series of orbits that gradually approach more closely to the Sun. During its 8$^th$ and 9$^th$ solar encounters, at a distance of ≍16 R $_\ensuremath\odot$ from the Sun, PSP sampled four extended periods in which the solar wind speed was measured to be smaller than the local Alfv\ en speed. These are the first in situ detections of sub-Alfv\ enic solar wind in the inner heliosphere by PSP. Here we explore properties of these samples of sub-Alfv\ enic solar wind, which may provide important previews of the physical processes operating at lower altitude. Specifically, we characterize the turbulence, anisotropy, intermittency, and directional switchback properties of these sub-Alfv\ enic winds and contrast these with the neighboring super-Alfv\ enic periods. Year of Publication 2022 Journal \apjl Volume 926 Number of Pages L1 Section Date Published feb ISBN URL DOI 10.3847/2041-8213/ac4a5c