Turbulent Density Fluctuations and Proton Heating Rate in the Solar Wind from 9–20 R ⊙

Abstract

We obtain scatter-broadened images of the Crab Nebula at 80 MHz as it transits through the inner solar wind in 2017 and 2016 June. These images are anisotropic, with the major axis oriented perpendicular to the radially outward coronal magnetic field. Using these data, we deduce that the density modulation index ($\delta {N}_{e}/{N}_{e}$) caused by turbulent density fluctuations in the solar wind ranges from $1.9\times {10}^{-3}$ to $7.7\times {10}^{-3}$ between 9 and 20 R ⊙. We also find that the heating rate of solar wind protons at these distances ranges from $2.2\times {10}^{-13}$ to $1.0\times {10}^{-11}\,\mathrm{erg}\,{\mathrm{cm}}^{-3}\,{{\rm{s}}}^{-1}$. On two occasions, the line of sight intercepted a coronal streamer. We find that the presence of the streamer approximately doubles the thickness of the scattering screen.