Testing for nonlinearity in the solar wind flow

We analyse a time series of the velocities of the low-speed stream measured by the Helios spacecraft in the inner heliosphere, which is a region of space dominated by the solar wind flow. We use a moving average (linear) filter to give a faithful representation of the systemʹs nonlinear behaviour. We have found that trajectories describing the system in phase space asymptotically approach the attractor of the low dimension of 3 to 4. These values are significantly different from the values computed for the surrogate data. Thus these results provide evidence that the inner heliosphere is likely to be a nonlinear chaotic system.