Non-Gaussian distribution function of AE-index fluctuations: Evidence for time intermittency

The probability distribution functions (Pdfs) of the AE-index fluctuations at different time scales have been investigated using a time series covering a period from January 01, 1978 to December 31, 1985. The Pdfs are always non Gaussian for time scales in the range 1-120 min both in quiet and disturbed periods. The scale dependence of the Pdfs indicates that AE-index is not characterized by a global time self-similarity, indicating that an intermittency phenomenon characterizes both phases. The results on Pdfs are compared with functional form, proposed by Castaing et al. [1990], to characterize intermittency phenomena in ordinary turbulent fluid flows. Moreover the relevance of these observations to the understanding of the magnetospheric dynamical configuration is pointed out.