how does the autocorrelation helps to understand the nonlinear dynamics

*_*Hello. I have a plot of autocorrelation where normal probalility of the 2 data sets are plotted against that 2 data sets and it shows both the datasets over lap on each other in the plot. but i dont understand how to describe the system nonlinear behaviour. (the corresponding parameters are chosen at nonlinear regime).

Does any one knows how do the autocorrelation characterises the linear and nonlinear system*_*