The anisotropic nature of the intermittent turbulence spectra in the solar wind

Abstract:

Intermittent structures in the solar wind turbulence carry important information on the turbulent non-linear dynamics and the heating effect of solar wind. However, the intermittency on small scales was rarely studied. Here we present a study of intermittent structures in the small timescale from 5 seconds to 100 seconds using the data from WIND observations in the high-speed solar wind. We find that the intermittent structures dominate the magnetic field turbulence in the scale. In this scale, the power spectrum of the intermittent structures with PVI >1 appears to be anisotropic with regards to the angle θ_RB between the direction of the local background magnetic field and the radial direction. The anisotropic nature in this sub-range is presented as follows: 1. At the scale τ=12s, the power spectral density of the intermittency withθ_RB = 84^o-90^o is one time larger than that of the intermittency with θ_RB =0^o-6^o; 2. The power spectrum becomes flatter as θ_RB increases, with an index of -2 at θ_RB =0^o-6^o and index of -1.6 at θ_RB =84^o-90^o; 3. The most probable value of the proton temperature distribution of the intermittent structures is 2.1×10⁵K, higher than the most probable proton temperature for the general solar wind (1.9×10⁵K); 4. The most probable value of the proton temperature of the intermittency with θ_RB =70^o-90^o is 2.2×10⁵K, clearly higher than that with θ_RB =0^o-20^o, which is 2.0×10⁵K. We think that the intermittent structures in the scale from 5s to 100s and their anisotropic spectral nature could be related to the non-linear interactions in the MHD turbulence, and they may have some influence on the dissipation processes in the solar wind turbulence.