Solar Wind Turbulent Spectrum at Plasma Kinetic Scales

Abstract

The description of the turbulent spectrum of magnetic fluctuations in the solar wind in the kinetic range of scales is not yet completely established. Here, we perform a statistical study of 100 spectra measured by the STAFF instrument on the Cluster mission, which allows us to resolve turbulent fluctuations from ion scales down to a fraction of electron scales, i.e., from ~10² km to ~300 m. We show that for k ρ _e in [0.03, 3] (which corresponds approximately to the frequency in the spacecraft frame f in [3, 300] Hz), all the observed spectra can be described by a general law E(k )vpropk ^-8/3 exp (- k ρ _e ), where k is the wavevector component normal to the background magnetic field and ρ _e the electron Larmor radius. This exponential tail found in the solar wind seems compatible with the Landau damping of magnetic fluctuations onto electrons.