Articles | Volume 17, issue 6
Research article
17 Dec 2010
Research article |  | 17 Dec 2010

Observational tests of the properties of turbulence in the Very Local Interstellar Medium

S. R. Spangler, A. H. Savage, and S. Redfield

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.