The MHD turbulence theory developed by Iroshnikov and Kraichnan predicts a $k^{-1.5}$ power spectrum. Solar wind observations, however, often show a $k^{-5/3}$ Kolmogorov scaling. Based on 3 years worth of Ulysses magnetic field data where over 28 000 current sheets are identified, we propose that the current sheet is the cause of the Kolmogorov scaling. We show that for 5 longest current-sheet-free periods the magnetic field power spectra are all described by the Iroshnikov-Kraichnan scaling. In comparison, for 5 periods that have the most number of current sheets, the power spectra all exhibit Kolmogorov scaling. The implication of our results is discussed.

• Received 13 December 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.125001