Probability Density Functions for the Variable Solar Wind

The solar wind is a complex plasma system in which structures, fluctuations and turbulence co-exist over multiple scales. Some aspects of this complexity can be described statistically only. In order to study the time evolution of field and plasma fluctuations we consider normal, log-normal, kappa and log-kappa probability distributions. We demonstrate that the shape of distributions shows a large variability controlled for example by the level of plasma compression. For the description of large-scale multi-source fluctuations in the solar wind nonlinear multiplicative rather than linear additive processes are needed. This indicates that the log-normal or the log-kappa distributions have to be used. The changing statistical features of fluctuations have a large impact on the physics of plasma heating.