Estimation of turbulent proton and electron heating rates via Landau damping constrained by Parker Solar Probe observations

TL;DR

This study models proton and electron heating rates in the solar wind using Parker Solar Probe data, demonstrating Landau damping's role in plasma heating and validating a turbulence cascade model across different plasma conditions.

Contribution

It applies a Landau damping-based turbulence model to PSP observations, providing new insights into ion-electron heating ratios in the inner heliosphere.

Findings

Model accurately describes over 39% of observed spectra.

Heating ratios strongly depend on plasma beta parameter.

Model's validity increases with higher plasma beta.

Abstract

The heating of ions and electrons due to turbulent dissipation plays a crucial role in the thermodynamics of the solar wind and other plasma environments. Using magnetic field and thermal plasma observations from the first two perihelia of the Parker Solar Probe (PSP), we model the relative heating rates as a function of radial distance, magnetic spectra, and plasma conditions, enabling us to better characterize the thermodynamics of the inner heliosphere. We employ the Howes et al. 2008 steady-state cascade model, which considers the behavior of turbulent, low-frequency, wavevector-anisotropic, critically balanced Alfv\'enic fluctuations that dissipate via Landau damping to determine proton-to-electron heating rates $Q_p/Q_e$. We distinguish ion-cyclotron frequency circularly polarized waves from low-frequency turbulence and constrain the cascade model using spectra constructed from the latter. We find that the model accurately describes the observed energy spectrum from over 39.4 percent of the intervals from Encounters 1 and 2, indicating the possibility for Landau damping to heat the young solar wind. The ability of the model to describe the observed turbulent spectra increases with the ratio of thermal-to-magnetic pressure, $\beta_p$, indicating that the model contains the necessary physics at higher $\beta_p$. We estimate high magnitudes for the Kolmogorov constant which is inversely proportional to the non-linear energy cascade rate. We verify the expected strong dependency of $Q_p/Q_e$ on $\beta_p$ and the consistency of the critical balance assumption.