Intermittency in the Solar Wind: A Comparison between Solar Minimum and Maximum using Ulysses Data

The solar wind is a highly turbulent and intermittent medium at frequencies between 10^-3 and 10^-1 Hz. Various models have been put forward in an attempt to understand this process better, and tested against solar wind data. The Ulysses spacecraft, in a polar orbit of the Sun, has now completed two fast-latitude scans, one at solar minimum and one at solar maximum. We have performed a comparison of two intermittency models - the well-known P model and the lognormal cascade model over this range of data. They were tested using fits to graphs of the structure function exponents g(q). At solar minimum, tests of both models indicated a high level of intermittency in the fast solar wind, and showed varied structure in the slow wind, indicating that the slow wind has no uniform origin. At solar maximum, slow wind dominated the heliosphere and the parameters show high variability throughout the scan, indicating that intermittency is indeed highly dependent on flow speed, or rather the details of the origin of the slow wind plasma. We have also fitted Castaing distributions to the data over several scales, and show that this is in many ways a more informative method than structure function analysis for studying intermittency.