The influence of intermittency on the spectral anisotropy of solar wind turbulence

The relation between the intermittency and the anisotropy of the power spectrum in the solar wind turbulence is studied by applying the wavelet technique to the magnetic field and flow velocity data measured by the WIND spacecraft. It is found that when the intermittency is removed from the turbulence, the spectral indices of the power spectra of the field and velocity turn out to be independent of the angle θ_RB between the direction of the local scale-dependent background magnetic field and the heliocentric direction. The spectral index becomes -1.63 ± 0.02 for magnetic field fluctuations and -1.56 ± 0.02 for velocity fluctuations. These results may suggest that the recently found spectral anisotropy of solar wind power spectra in the inertial range could result from turbulence intermittency. As a consequence, a new concept is here proposed of an intermittency-associated sub-range of the inertial domain adjacent to the dissipation range. Since spectral anisotropy was previously explained as evidence for the presence of a "critical balance" type turbulent cascade, and also for the existence of kinetic Alfvén waves, this new finding may stimulate fresh thoughts on how to analyze and interpret solar wind turbulence and the associated heating.