Wavelet analysis applied to magnetograms: Singularity detections related to geomagnetic storms

When the interplanetary magnetic field carried by the solar wind opposes to the Earth intrinsic magnetic field, a substantial transfer of energy into the terrestrial magnetosphere takes place. If this condition persists for several hours, the magnetosphere becomes very disturbed. As a result, at mid-to-low latitudes a ring current starts to develop and at high latitudes ionospheric currents (electrojet and field-aligned currents) dominate. The ring current provides the geomagnetic conditions for magnetic storms to settle down. Wavelet analysis is becoming an usual tool since they allow the decomposition of data, functions or operators into different frequency or scale components. Accordingly, wavelet transforms seem to be suited to analyze short-lived high-frequency phenomena such as discontinuities (shocks) in signals and transient structures. In this work, the remarkable ability of wavelets to highlight the singularities associated with discontinuities present in the horizontal component of the Earth's magnetic field is explored. Magnetograms obtained at five magnetic stations for two geomagnetic storms have been analyzed by a Daubechies orthogonal wavelet transform. The wavelet coefficient magnitudes at three levels have been studied. In both cases, the physical discontinuities in the horizontal component of the geomagnetic field are clearly detected by means of these coefficients identifying the disturbed interval related to geomagnetic storms. Wavelet analysis has proved to be a useful tool in the identification of the geomagnetic storms using non-processed data.