Turbulence in the solar wind: spectra from Voyager 2 data at 5 AU

Abstract

Fluctuations in the flow velocity and magnetic fields are ubiquitous in the\nSolar System. These fluctuations are turbulent, in the sense that they are\ndisordered and span a broad range of scales in both space and time. The study\nof solar wind turbulence is motivated by a number of factors all keys to the\nunderstanding of the Solar Wind origin and thermodynamics. The solar wind\nspectral properties are far from uniformity and evolve with the increasing\ndistance from the sun. Most of the available spectra of solar wind turbulence\nwere computed at 1 astronomical unit, while accurate spectra on wide frequency\nranges at larger distances are still few. In this paper we consider solar wind\nspectra derived from the data recorded by the Voyager 2 mission during 1979 at\nabout 5 AU from the sun. Voyager 2 data are an incomplete time series with a\nvoids/signal ratio that typically increases as the spacecraft moves away from\nthe sun (45% missing data in 1979), making the analysis challenging. In order\nto estimate the uncertainty of the spectral slopes, different methods are\ntested on synthetic turbulence signals with the same gap distribution as V2\ndata. Spectra of all variables show a power law scaling with exponents between\n-2.1 and -1.1, depending on frequency subranges. Probability density functions\n(PDFs) and correlations indicate that the flow has a significant intermittency.\n