| In spite of a large number of papers dedicated to the study of MHD
turbulence in the solar wind there are still some simple
questions which have never been sufficiently addressed, such as:
a) Do we really know how the magnetic field vector orientation
fluctuates in space? b) What are the statistics followed by the
orientation of the vector itself? c) Do the statistics change as
the wind expands into the interplanetary space?
A better understanding of these points can help us to better
characterize the nature of interplanetary fluctuations and can
provide useful hints to investigators who try to numerically
simulate MHD turbulence.
This work follows a recent paper presented by some of the authors
which shows that these fluctuations might resemble a sort of
random walk governed by Truncated Lévy Flight statistics.
However, the limited statistics used in that paper did not allow for
final conclusions but only speculative hypotheses. In this work
we aim to address the same problem using more robust statistics
which, on the one hand, forces us not to consider velocity fluctuations
but, on the other hand, allows us to establish the nature of the
governing statistics of magnetic fluctuations with more
confidence.
In addition, we show how features similar to those found in the
present statistical analysis for the fast speed streams of solar
wind are qualitatively recovered in numerical simulations of the
parametric instability. This might offer an alternative viewpoint
for interpreting the questions raised above. |