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In the lower solar coronal regions where the magnetic field is dominant, theAlfven speed is much higher than the wind speed. In contrast, the near-Earthsolar wind is strongly super-Alfvenic, i.e., the wind speed greatly exceeds theAlfven speed. The transition between these regimes is classically described asthe "Alfven point" but may in fact occur in a distributed Alfven criticalregion. NASA's Parker Solar Probe (PSP) mission has entered this region, as itfollows a series of orbits that gradually approach more closely to the sun.During its 8th and 9th solar encounters, at a distance of 16 solar radii fromthe Sun, PSP sampled four extended periods in which the solar wind speed wasmeasured to be smaller than the local Alfven speed. These are the first in-situdetections of sub-Alfvenic solar wind in the inner heliosphere by PSP. Here weexplore properties of these samples of sub-Alfvenic solar wind, which mayprovide important previews of the physical processes operating at loweraltitude. Specifically, we characterize the turbulence, anisotropy,intermittency, and directional switchback properties of these sub-Alfvenicwinds and contrast these with the neighboring super-Alfvenic periods.

Sub-Alfvenic Solar Wind observed by PSP: Characterization of Turbulence, Anisotropy, Intermittency, and Switchback