Prediction of the Proton-to-Total Turbulent Heating in the Solar Wind

TL;DR

This study predicts the proton-to-total turbulent heating ratio in the solar wind using a recent turbulent heating model, finding good agreement with observations beyond 0.8 AU but underestimating proton heating closer to the Sun due to cascade limitations.

Contribution

It applies a turbulent heating prescription to predict proton heating ratios in the solar wind and compares these predictions with empirical data across different heliocentric distances.

Findings

Good agreement with empirical data for R > 0.8 AU.

Underestimation of proton heating at smaller radii due to cascade reaching proton cyclotron frequency.

Turbulent cascade likely reaches proton cyclotron frequency at R < 0.8 AU.

Abstract

This paper employs a recent turbulent heating prescription to predict the ratio of proton-to-total heating due to the kinetic dissipation of Alfvenic turbulence as a function of heliocentric distance. Comparing to a recent empirical estimate for this turbulent heating ratio in the high-speed solar wind, the prediction shows good agreement with the empirical estimate for R >~ 0.8 AU, but predicts less ion heating than the empirical estimate at smaller heliocentric radii. At these smaller radii, the turbulent heating prescription, calculated in the gyrokinetic limit, fails because the turbulent cascade is predicted to reach the proton cyclotron frequency before Landau damping terminates the cascade. These findings suggest that the turbulent cascade can reach the proton cyclotron frequency at R <~ 0.8 AU, leading to a higher level of proton heating than predicted by the turbulent heating prescription in the gyrokinetic limit. At larger heliocentric radii, R >~ 0.8 AU, this turbulent heating prescription contains all of the necessary physical mechanisms needed to reproduce the empirically estimated proton-to-total heating ratio.