Wavelet-Coherence and multifractal analysis of Geomagnetic disturbances

Abstract

This work explores the solar wind–magnetosphere interaction during the major geomagnetic disturbances of 2024, with particular focus on the May 11 storm. We examined how variations in the interplanetary magnetic field’s component and solar wind dynamic pressure ( ) translate into magnetic perturbations on Earth. The response of the terrestrial system was evaluated using horizontal field measurements from mid-latitude observatories together with the global SYM-H and auroral AL indices. Time–frequency analysis with wavelet coherence exposed the highly scale-dependent and non-stationary character of the coupling process. In addition, multifractal detrended fluctuation analysis revealed a marked reduction in the Hurst exponent during the May 11 event. This feature was present in both mid-latitude and auroral electrojet records but absent in SYM-H, highlighting distinct regional responses. The absence of this feature in the ring current index, coupled with its presence in mid-latitude and auroral records, indicates that the auroral oval expanded equatorward, leaving a clear imprint at lower latitudes. Our findings highlight that combining localized and global perspectives is essential to fully capture the diverse impacts of severe geomagnetic storms on the near-Earth environment.