Abstract
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. Information provided by these spectroscopic measurements includes values for ξ, the root-mean-square velocity fluctuation due to turbulence in these clouds, and T, 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. We ask if the spectroscopically-deduced parameters such as ξ and T depend on the direction on the sky. We also consider the degree to which a single temperature T and turbulence parameter ξ account for the spectral line widths of ions with a wide range of masses. A preliminary examination of the published data shows no 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. Possible physical reasons for these differences are discussed.
Highlights
It is arguably the case that the best experimental data for studying magnetohydrodynamic (MHD) turbulence come from spacecraft measurements of turbulent fluctuations in the solar wind
We first consider whether the turbulence in the Local Clouds possesses transverse velocity fluctuations, in which the fluid motion is perpendicular to the large scale magnetic field
We conclude that there is no strong evidence for anisotropy of turbulent velocity fluctuations in the Local Clouds, as would occur if the turbulence is transverse in the sense of solar wind turbulence
Summary
It is arguably the case that the best experimental data for studying magnetohydrodynamic (MHD) turbulence come from spacecraft measurements of turbulent fluctuations in the solar wind. Among the many reviews of the subject is the monograph by Tu and Marsch (1995) and the review article by Goldstein et al (1995). Another nearby plasma with extensive diagnostics ( not, as yet, in situ measurements) is the solar corona. Measurements and observations of solar wind and coronal turbulence provide the best data for testing our ideas on the nature of MHD turbulence, and guide our thinking about turbulence in other astrophysical plasmas. We discuss the degree to which the turbulence in one well-diagnosed plasma, the partially ionized media which constitute the Local Clouds in the Very Local Interstellar Medium (VLISM), have properties similar to those of turbulence in the solar wind and solar corona
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