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Investigates harmonic changes in planetary geomagnetic index Ap, suggesting new insights into geomagnetic activity.
Fourier spectral analysis is applied to the planetary geomagnetic index Ap for the February 2001, 2003, and 2017 time intervals. We investigate how Fourier coefficients change in time with respect to geomagnetic activity. A detailed analysis of the 13–14 February 2001 substorm revealed that higher harmonics were suppressed during the event, contrary to what was expected.
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Vandas et al. (2026) studied this question.
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