Observations of evolving turbulence in the polar solar wind

Abstract

The Ulysses magnetic field experiment has measured the heliospheric magnetic field in solar wind flows from the Sun's Southern polar coronal hole over a wide range of heliolatitudes and distances. We present an analysis of more than one year of data, covering a latitude range of 40° to 80°S and a distance range of 4.0 to 1.7 AU. We extend an earlier analysis of Ulysses magnetic field data and, by calculating structure functions, demonstrate that the spectrum of fluctuations in the magnetic field changed along the orbit of Ulysses within polar flows and that this change is a result of the variation in Ulysses' distance from the Sun, rather than its latitude. We interpret this change as being due to the development of turbulence in the polar solar wind.