A wavelet based method to remove the long term periodicities of geophysical time series

Abstract In this work it is shown how to remove the long-term periodicities present in geophysical time series using the Daubechies (db4) wavelet functions. This methodology consists in extraction of part of the energy from large scales (long periods) determined through of a threshold chosen from the variance analysis performed by scale. The Morlet wavelet transform was used in order to show that this procedure removes the energy from long-term periodicities while preserving all original frequencies. This method is applied to a case study of magnetotail response to interplanetary magnetic field (IMF) Bz fluctuations during a high-intensity long-duration continuous AE activity (HILDCAA) event.