On the variations of the solar wind magnetic field about the Parker spiral direction

Using ACE, Helios, and OMNI2 measurements, the direction vectors of the solar wind magnetic field are statistically analyzed. Two populations of direction vectors are found: a Gaussian distribution about the Parker spiral direction and an isotropic population. Examination of the isotropic population finds ejecta, long-duration non-Parker spiral intervals, magnetic depressions, heliospheric-current-sheet crossings, and spillover from the Gaussian population. Via numerical experiments, spillover in spherical coordinates from the Gaussian population into the isotropic population is explored and quantified. ACE measurements find that the angular width of the Gaussian Parker spiral population increases with solar wind speed. Examining the properties of the two populations year by year, no clear solar-cycle trends are found. Inside the compression regions of corotating interaction regions, the longitudinal width of the Gaussian Parker spiral population decreases by about a factor of two, while the latitudinal width of that population is approximately unchanged. Helios measurements find that the angular width of the Gaussian Parker spiral population decreases closer to the Sun, and the isotropic fraction decreases. The flux tube model of the solar wind structure is compared with spacecraft measurements: the model approximately agrees with the Helios behavior versus the distance from the Sun, and the model approximately agrees with the ACE behavior in the corotating interaction region compressions.