Spectrum of kinetic plasma turbulence at 0.3-0.9 au from the Sun
Abstract
We investigate spectral properties of solar wind turbulence that constitutes a natural example of turbulence in weakly collisional astrophysical plasma accessible by in-situ observations. Here, we focus on properties of turbulent magnetic fluctuations on particle characteristic (kinetic) scales using Helios search coil magnetometer measurements in the fast solar wind in the inner heliosphere. We show that the magnetic power spectra between 0.3 and 0.9 AU from the Sun have a generic shape ~f-8/3exp(-f/fd) where the dissipation frequency fd is close to the Doppler shifted frequency of the electron Larmor radius fρe. This behavior is statistically significant, all observed kinetic spectra are well described by this model, with fd=fρe/1.8. These results, together with the previous observations with Cluster at 1 AU [Alexandrova et al. 2012, APJ], indicate that between 0.3 AU and 1 AU, similar physical processes govern kinetic-scale turbulence and the electron Larmor radius scale plays an important role in the dissipation of solar wind turbulence.