SOME POSSIBLE EVIDENCE FOR A CHAOTIC GEOMAGNETIC-FIELD FROM OBSERVATIONAL DATA

The behaviour of the geomagnetic field as observed almost continuously at three European locations over the last 130 years is investigated b y means of a non-linear forecasting approach. The analysis of the data in terms of first-differences (secular variation) of the horizontal m agnetic components made in phase space with the simplex technique seem s to exclude the pre-eminence of any stochastic or periodic behaviour. The dimensionality of the underlying non-linear process and the corre sponding largest positive Lyapunov exponent are estimated. The results give some evidence that the geomagnetic field evolves as a non-linear chaotic system with unpredictable behaviour after times greater than a few years, confirming the common practice of updating global models of the geomagnetic field every 5 years.