Modelling Reflexivity with a Time Series Model

[CyberneticAlph]

I'm new to this forum so hi to everyone!

I would like to find a time series model that is capable of modelling two time series with following properties:

1) consider time series X and Y. X is influencing Y positively and vice versa so that they move in the same direction. However one time series is influencing the other one stronger, so that the move more and more apart.

2) if they have moved too much apart a trend reversal sets in both time series.

You can find an illustration of the two time series here: http://www.georgesoros.com/wp-content/u ... 0004_c.gif

Does anyone know a proper time series model for this dynamik? Thanks in advance!