Parker Sampled Fast Wind Below the Alfvén Surface

Near its 23rd perihelion, Parker Solar Probe sampled an extended sub-Alfvénic interval at roughly ten solar radii with speeds mostly above 400 kilometers per second. The authors identify it as the first polar-coronal-hole-like fast stream observed inside the sub-Alfvénic corona. Its turbulence was already developed, strongly transverse and highly imbalanced despite the close distance. The source is inferred as a large equatorial coronal hole rather than directly traced to a polar hole.