WHERE DOES FLUID-LIKE TURBULENCE BREAK DOWN IN THE SOLAR WIND?

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 Alfv ́ n wave fluctuations above the ion-cyclotron frequency or to whistler turbulence above e the frequency corresponding to the proton gyroradius. Using solar wind data, we show that the observed high- frequency 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.