Observational Tests of the Properties of Turbulence in the Very Local Interstellar Medium

TL;DR

This study uses spectroscopic data to analyze turbulence properties in the Very Local Interstellar Medium, comparing them to solar wind turbulence, and finds notable differences in anisotropy and ion heating.

Contribution

It provides the first observational assessment of turbulence characteristics in the VLISM and compares these with solar wind turbulence, highlighting key differences.

Findings

No evidence of anisotropy in velocity fluctuations or temperature.

Larmor radius-dependent ion heating is not observed.

Turbulence in the VLISM differs from solar wind turbulence.

Abstract

The Very Local Interstellar Medium (VLISM) contains clouds which consist of partially-ionized plasma. These clouds can be effectively diagnosed via high resolution optical and ultraviolet spectroscopy of the absorption lines they form in the spectra of nearby stars. Among the information provided by these spectroscopic measurements are the root-mean-square velocity fluctuation due to turbulence in these clouds and the ion temperature, which may be partially determined by dissipation of turbulence. We consider whether this turbulence resembles the extensively studied and well-diagnosed turbulence in the solar wind and solar corona. Published observations are used to determine if the velocity fluctuations are primarily transverse to a large-scale magnetic field, whether the temperature perpendicular to the large scale field is larger than that parallel to the field, and whether ions with larger Larmor radii have higher temperatures than smaller gyroradius ions. Although a thorough investigation of the data is underway, a preliminary examination of the published data shows neither evidence for anisotropy of the velocity fluctuations or temperature, nor Larmor radius-dependent heating. These results indicate differences between solar wind and Local Cloud turbulence.