Kolmogorov versus Iroshnikov-Kraichnan spectra: Consequences for ion heating in the solar wind

TL;DR

This study compares Kolmogorov and Iroshnikov-Kraichnan turbulence spectra to understand their effects on ion heating in the solar wind, finding IK scaling better matches observed temperature profiles and turbulence correlation lengths.

Contribution

It introduces a solar wind heating model using IK spectral scaling and demonstrates its improved agreement with observations over Kolmogorov-based models.

Findings

IK scaling yields higher proton temperatures consistent with observations.

IK-based turbulence correlation length aligns better with observational trends.

Including pickup ion effects enhances model accuracy regardless of spectral scaling.

Abstract

Whether the phenomenology governing MHD turbulence is Kolmogorov or Iroshnikov-Kraichnan (IK) remains an open question, theoretically as well as observationally. The ion heating profile observed in the solar wind provides a quantitative, if indirect, observational constraint on the relevant phenomenology. Recently, a solar wind heating model based on Kolmogorov spectral scaling has produced reasonably good agreement with observations, provided the effect of turbulence generation due to pickup ions is included in the model. Without including the pickup ion contributions, the Kolmogorov scaling predicts a proton temperature profile that decays too rapidly beyond a radial distance of 15 AU. In the present study, we alter the heating model by applying an energy cascade rate based on IK scaling, and show that the model yields higher proton temperatures, within the range of observations, with or without the inclusion of the effect due to pickup ions. Furthermore, the turbulence correlation length based on IK scaling seems to follow the trend of observations better.