Evaluation and analysis of Voyager 1 48-s resolution magnetic field data

Abstract

The aim of this paper is to provide information on the radial dependence of turbulence quantities as input for ab initio numerical cosmic-ray modulation models. We present an evaluation and analysis of 48-s resolution Voyager 1 data for the normal component of the magnetic field. These data were preprocessed to fill in data gaps and filter out spurious peaks. The effectiveness of this process is illustrated for a sample data set, for which we show that the underlying spectrum is indeed Kolmogorov. We use a second-order structure function to find correlation times, and also the spectral index and spectral level in the inertial range from expressions derived by Huang et al. (2010). The usefulness of the second-order structure function for data with significant gaps is illustrated by using synthetic data. Gaps up to 68% cause changes of less than 5% in the quantities that we calculate. We show that beyond about 20 au there are significant changes in the behaviour of the magnetic field magnitude and the inertial range spectral index, neither of which has a reasonable explanation. We find that the ratio δBN/BN remains almost constant out to 20 au, that the correlation times is consistent with results from other studies, and that the spectral index in the inertial range is consistent with the Kolmogorov value. A new result is that we could infer that the break between the energy- and the inertial range has a radial dependence that is consistent with that of the correlation scale.