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 Alfven 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 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.