Analysis of the solar wind flow during an activity cycle

We have analyzed the time series of solar wind velocity fluctuations measured by the Helios spacecraft in the inner heliosphere corresponding to solar cycle 21. To understand the local dynamics of fluctuations in the slow speed wind velocity, we have calculated the largest Lyapunov exponent and its variance for a total of 18 data sets measured at a distance of 0.32 AU from the sun in the years 1975–1982. The Lyapunov exponents obtained are positive for all data sets but show large variance for some of the time series, suggesting inherent changes in the dynamics over the solar cycle. Furthermore, estimation of the correlation dimension for each of the 18 time series indicates presence of low-dimensional chaotic behavior in the underlying dynamics.