  We study the vortex dynamics in an evolutive flow. We carry out the
statistical analysis of the resulting time series by means of the joint use of
a compression and an entropy diffusion method. This approach to complexity
makes it possible for us to establish that the time series emerging from the
wavelet analysis of the vortex dynamics is a weakly chaotic process driven by a
hidden dynamic process. The complexity of the hidden driving process is shown
to be located at the border between the stationary and non-stationary state.
