Alfvén Speed Transition Zone in the Solar Corona

The Alfvén radius, rA, at which solar wind radial outflow speed exceeds the wave speed, is an important parameter in understanding evolution extended corona. mean angular momentum scales with axisymmetric steady-state approximation, so radius often referenced study of corotation and dynamics. derived from magnetic-field intensity plasma mass density. In inner coronal regions, these parameters were previously estimated using empirical models based on remote sensing observations or inverse-square scaling measurements 1 au. Parker Solar Probe (PSP) orbital encounters now provide situ to determine speeds within 30 radii heliocenter. We combined PSP solar-wind calculated corona profile studies. zone super-Alfvénic cross over occur heliocentric distance 17.9 ± 2.1 R⊙ for slow winds low heliolatitude a near-minimum activity state. Our rA values constrain flux 3.5 1.01 × 1022 N m sr−1, reinforcing recent results by direct particle flows.