Turbulent density fluctuations and proton heating rate in the solar wind from 9-20~R_{\odot}

TL;DR

This study measures turbulent density fluctuations and proton heating rates in the solar wind between 9-20 solar radii using radio observations of the Crab Nebula, revealing anisotropic turbulence and the influence of coronal streamers.

Contribution

It provides new quantitative estimates of density fluctuation levels and proton heating rates in the inner solar wind, highlighting the impact of streamers on scattering properties.

Findings

Density modulation index ranges from 1.9e-3 to 7.7e-3 between 9-20 R_sun.

Proton heating rate varies from 2.2e-13 to 1.0e-11 erg cm^{-3} s^{-1}.

Streamer presence doubles the scattering screen thickness.

Abstract

We obtain scatter broadened images of the Crab Nebula at 80 MHz as it transits through the inner solar wind in June 2016 and 2017. 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 9-20 R_{\odot}. 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} ~erg~cm^{-3}~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.