Relative heating of ions and electrons in the young solar wind due to turbulent dissipation mediated via Landau damping

Abstract:

The relative heating of ions and electrons due to turbulent dissipation plays a crucial role in the thermodynamics of the solar wind. Previous works have used in situ observations from Helios, Ulysses, and Voyager to construct profiles of ion and electron heating rates as a function of distance from the Sun, by making a variety of theoretical assumptions regarding the turbulent distribution of power and the accessible damping mechanisms. These in situ measurements of the solar wind have been limited to a heliocentric distance of greater than 0.29 au. Parker Solar Probe (PSP) will eventually provide such measurements down to 0.046 au. One particular theoretical model, developed in Howes et al. 2008 and expanded in Kunz et al. 2018, determines these heating rates as a function of observable plasma parameters when dissipation is mediated by Landau damping. The model considers a steady-state cascade of wavevector anisotropic turbulent fluctuations from the inertial to dissipation range, connecting the MHD and kinetic descriptions. We apply this model to observations from the first two PSP encounters, characterizing how the relative heating rates vary as a function of radial distance, plasma and solar wind parameters, and solar wind source, and compare these results to previous analysis of heating rates. Our work would illuminate how energy is partitioned in the young solar wind.