New Insights Gained From the Study of the PDF of Small Scale IMF Fluctuations

Interplanetary MHD fluctuations are strongly affected by the solar wind radial expansion. In a previous investigation we studied the radial evolution of the probability distribution function (PDF) of magnetic field and velocity fluctuations within the inner heliosphere and found that the behaviour of these fluctuations tended to resemble a Levy-flight statistics, especially with increasing heliocentric distance from the sun. We concluded that the observed behaviour is mainly due to a competing action between stochastic, propagating fluctuations and convected structures, both contributing to solar wind turbulent fluctuations. These two ingredients, which experience a different radial evolution, are represented by propagating Alfvénic fluctuations and convected flux tubes, respectively. In the present analysis we looked in more detail at the PDF of high resolution magnetic field fluctuations within the inner heliosphere gaining new interesting insights about the nature of these fluctuations and the topology of interplanetary magnetic field at small scale. We finally discuss initial results from a simple model which tries to resemble observations within fast and slow wind with some success.