Authors: Rohit Chhiber (NASA GSFC and U Delaware)

Observations from Parker Solar Probe’s first several orbits are used to investigate the helioradial evolution of probability density functions (pdfs) of fluctuations of magnetic-field components between ∼13 and 200 solar radii. Transformation of the magnetic-field vector to a local mean-field coordinate system permits examination of anisotropy relative to the mean magnetic-field direction. Attention is given to effects of averaging-interval size, with a focus on energy-containing scales. It is found that pdfs of the perpendicular fluctuations are well approximated by a Gaussian function, with the parallel fluctuations less so: kurtoses of the latter are generally larger than 10, and their pdfs indicate increasing skewness with decreasing distance r from the Sun. The behavior of the skewness of parallel fluctuations may be explained by the increasing Alfvenicity of the fluctuations. The ratio of perpendicular to parallel variances is greater than unity; this variance anisotropy becomes stronger with decreasing r. The ratio of the total rms fluctuation strength to the mean-field magnitude decreases with decreasing r, with a value ∼0.8 near 1 au and ∼0.3 near 0.07 au; the ratio is well approximated by an r^(1/4) power law. Preliminary comparison of sub-Alfvenic and super-Alfvenic intervals indicates that the skewness and intermittency of parallel fluctuations is diminished in sub-Alfvenic wind. These findings improve our understanding of the radial evolution of turbulence in the solar wind, and have implications for related phenomena such as energetic-particle transport in the inner heliosphere.