Turbulent density fluctuations in the solar wind

TL;DR

This paper introduces a general structure function (GSF) for more accurate modeling of density turbulence effects in the solar wind, improving scatter-broadening estimates and enabling new insights into solar wind heating.

Contribution

The paper proposes the GSF as a superior alternative to asymptotic approximations for analyzing solar wind density turbulence and applies it to estimate solar wind heating rates from observational data.

Findings

GSF provides more accurate predictions than asymptotic approximations.

First estimates of the solar wind density modulation index from Sun to Earth.

Quantitative constraints on solar wind heating rates due to turbulence.

Abstract

Treatments of the radio scattering due to density turbulence in the solar wind typically employ asymptotic approximations to the phase structure function. We use a general structure function (GSF) that straddles the asymptotic limits and quantify the relative error introduced by the approximations. We show that the regimes where GSF predictions are accurate than those of its asymptotic approximations is not only of practical relevance, but are where inner scale effects influence the estimate of the scatter-broadening. Thus we propose that GSF should henceforth be used for scatter broadening calculations and estimates of quantities characterizing density turbulence in the solar corona and solar wind. In the next part of this thesis we use measurements of density turbulence in the solar wind from previously publish observations of radio wave scattering and interplanetary scintillations. Density fluctuations are inferred using the GSF for radio scattering data and existing analysis methods for IPS. Assuming that the density fluctuations below proton scales are due to kinetic Alfv`en waves, we constrain the rate at which the extended solar wind is heated due to turbulent dissipation. These results provide the first estimates of the density modulation index and the solar wind heating rate all the way from the Sun to the Earth.