Rank ordering multifractal analysis of the auroral electrojet index

In the second half of the 90s interest grew on
the complex features of the magnetospheric dynamics in response
to solar wind changes. An important series of papers
were published on the occurrence of chaos, turbulence
and complexity. Among them, particularly interesting was
the study of the bursty and fractal/multifractal character of
the high latitude energy release during geomagnetic storms,
which was evidenced by analyzing the features of the Auroral
Electrojet (AE) indices. Recently, the multifractal features of
the small time-scale increments of AE-indices have been criticized
in favor of a more simple fractal behavior. This is particularly
true for the scaling features of the probability density
functions (PDFs) of the AE index increments. Here, after
a brief review of the nature of the fractal/multifractal features
of the magnetospheric response to solar wind changes, we investigate
the multifractal nature of the scaling features of the
AE index increments PDFs using the Rank Ordering Multifractal
Analysis (ROMA) technique. The ROMA results
clearly demonstrate the existence of a hierarchy of scaling
indices, depending on the increment amplitude, for the data
collapsing of PDFs relative to increments at different time
scales. Our results confirm the previous results by Consolini
et al. (1996) and the more recent results by Rypdal and Rypdal
(2010).

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