The rate at which the solar wind extracts angular momentum from the Sun has been predicted by theoretical models for many decades , and yet we lack a conclusive measurement from in-situ observations .
In this letter we present a new estimate of the time-varying angular momentum flux in the equatorial solar wind , as observed by the Wind spacecraft from 1994-2019 .
We separate the angular momentum flux into contributions from the protons , alpha particles , and magnetic stresses , showing that the mechanical flux in the protons is \sim 3 times larger than the magnetic field stresses .
We observe the tendency for the angular momentum flux of fast wind streams to be oppositely signed to the slow wind streams , as noted by previous authors .
From the average total flux , we estimate the global angular momentum loss rate of the Sun to be 3.3 \times 10 ^ { 30 } erg , which lies within the range of various MHD wind models in the literature .
This angular momentum loss rate is a factor of \sim 2 weaker than required for a Skumanich-like rotation period evolution ( \Omega _ { * } \propto stellar age ^ { -1 / 2 } ) , which should be considered in studies of the rotation period evolution of Sun-like stars .