Outer Heliospheric Turbulence and the Angular Broadening of Radio Sources from the Voyager Data

Abstract

The properties of density turbulence are important in estimating the angular broadening of radio sources in the outer heliosphere and very local interstellar medium (VLISM). We calculate the density variance, inner scale, correlation length of the velocity, and relative density amplitude as a function of radial distance using plasma and magnetometer data from the Voyager 2 spacecraft over the period 1977 to 2018. We apply three different techniques to estimate the density turbulence amplitude, including an inner scale, using the Voyager 2 data. Related analyses compare Voyager data determined turbulence amplitudes with results from the density turbulence theories of Zank et al. [49, 50] and Bellamy et al. [6]. Theoretical predictions and observations show strong similarities: both qualitatively and quantitatively. In addition, the predicted turbulence amplitudes show radial trends similar to those observed. The numerical prediction of the scattering angle uses a turbulence spectrum that includes an inner scale. The numerical and analytic results are compared, and we find similar radial trends.