Multiscale Nonlinear Analysis of AE and AU Geomagnetic Activity Indices during the 2014 Solar Maximum

Abstract

This study investigates the variability and chaoticity behaviour of hourly geomagnetic field parameters (Auroral
Electrojet and Upper Auroral Electrojet) data from January 1st – December 31st 2014, corresponding to peak solar
activity obtained from the OMINIWEB dataset. Nonlinear time series techniques such as Embedding Taken’s and
Wavelet Power Spectrum analysis were applied to reconstruct the hidden system dynamics and energy distribution
respectively. Analysis of AE and AU indices exhibited similar irregular and highly fluctuating patterns particularly
during geomagnetic disturbances. Embedding Taken’s showed that delay time  = 12 and embedding dimension
m = 7 for both indices, these values were used for phase space reconstruction. Computed Largest Lyapounov
Exponent (LE) with value 0.152 for AE index and 0.132 for AU index (positive values) indicate the presence of
deterministic chaos within the geomagnetic system. Hurts exponent analysis revealed that AU and AE indices
displayed values of 0.96 and 0.78 respectively corresponding to perfectly deterministic process with strong
persistence. The Wavelet Power Spectrum (WPS) analysis indicated significant energy concentrations, with
average value of approximately 16,000mm2 for AE and 60,000mm2 for AU, confirming strong temporal variability
in both indices. Overall, the results demonstrated that temporal evolution of AE and AU indices are governed by
an underlying chaotic dynamics; behaviour arising from the complex interaction between solar wind conditions,
magnetotail energy storage processes, and ionospheric current dynamics capable of triggering geomagnetic storms
which enhances system instability. This study therefore provides valuable insight into nonlinear dynamics of
geomagnetic activity during periods of intense solar forcing.