Comparative study of ground-based and satellite observations of Pc5 geomagnetic pulsations during solar cycle 23

Abstract

Abstract Pc5 geomagnetic pulsations (PGPs) are ultra-low frequency (ULF) waves within the 1–7 mHz frequency band observed both in space and on the ground. PGPs offer versatile methods for studying the interaction between the magnetosphere and ionosphere in space. This study presents a comparative analysis of Pc5 pulsations observed in space and on the ground. The dataset used is the magnetic field-aligned readings obtained from the Geostationary Operational Environmental Satellite-10 (GOES-10) and ground-based magnetometer stations from the Svalbard network located in the auroral zone during solar cycle 23. Using the Empirical Mode Decomposition (EMD) method, we transformed the magnetic field time series from GOES-10 into the mean field-aligned coordinate system. PGPs were extracted from the toroidal component using a bandpass Butterworth filter. In addition, Pc5 waves were extracted from the Bx component of the ground magnetometer stations to enable effective comparison. Before conducting the comparative analysis, Pc5 events on the ground and in space were denoised using the heuristic Stein Unbiased Risk Estimate (SURE) approach with soft thresholding. Consequently, a good coherence between events from space and on the ground was observed, indicating the possibility of the same generation source. However, space-borne Pc5 events have a smaller average amplitude of 12 nT compared to Pc5 events observed on the ground, having an average amplitude of 139 nT. We attributed this difference in amplitude to the transformative mechanisms during the wave's propagation to the ground. The average percentage of occurrence of Pc5 geomagnetic pulsations observed in space was found to be 74%, and that on the ground was 92%. The percentage difference was found to be due to the spatial distribution of these waves. The integrity of the retrieved events was demonstrated by the strong correlation between the Kp index and events extracted from the ground magnetometer stations. Our results contribute significantly to the understanding of Pc5 geomagnetic pulsations within the space weather community. These findings will aid in developing forecasting and predictive models, enabling more effective studies of these waves and helping to mitigate their potential impacts on human activities and infrastructure.