Where does fluid-like turbulence break down in the solar wind?

Abstract

Power spectra of the magnetic field in solar wind display a Kolmogorov law f-5/3 at intermediate range of frequencies f, say within the inertial range. Two spectral breaks are also observed: one separating the inertial range from an f-1 spectrum at lower frequencies, and another one between the inertial range and an f-7/3 spectrum at higher frequencies. The breaking of fluid-like turbulence at high frequencies has been attributed to either the occurrence of kinetic Alfvén wave fluctuations above the ion-cyclotron frequency or to whistler turbulence above the frequency corresponding to the proton gyroradius. Using solar wind data, we show that the observed highfrequency spectral break seems to be independent of the distance from the Sun, and then of both the ion-cyclotron frequency and the proton gyroradius. We suppose that the observed high-frequency break could be either caused by a combination of different physical processes or associated with a remnant signature of coronal turbulence. © 2010. The American Astronomical Society. All rights reserved.