Turbulence Driving by Interstellar Pickup Ions in the Outer Solar Wind

TL;DR

This paper investigates how interstellar pickup ions influence turbulence in the outer solar wind, proposing a self-regulation mechanism that aligns with observed turbulence levels and solar wind heating.

Contribution

It introduces a new model where PUI energization by turbulence explains the observed turbulence levels and reduces fluctuation energy compared to previous predictions.

Findings

Energization of PUIs leads to more spherical distributions.

Reduces fluctuation energy to observed levels.

Supports a self-regulation mechanism for turbulence and heating.

Abstract

We revisit the question of how the unstable scattering of interstellar pickup ions (PUIs) may drive turbulence in the outer solar wind, and why the energy released into fluctuations by this scattering appears to be significantly less than the standard bispherical prediction. We suggest that energization of the newly picked-up ions by the ambient turbulence during the scattering process can result in a more spherical distribution of PUIs, and reduce the generated fluctuation energy to a level consistent with the observations of turbulent intensities and core solar wind heating. This scenario implies the operation of a self-regulation mechanism that maintains the observed conditions of turbulence and heating in the PUI-dominated solar wind.