Wavelet analysis has been formalized extensively due to the efforts of mathematicians, physics and engineers in the last two decades. It has generated a tremendous interest in these communities both in theoretical and applied areas, in such a way that wavelet analysis is also considered now as a nucleus of shared aspirations and ideas. Initially applied to seismic signal studies in geophysics in the 80's, wavelet techniques have been explored in the atmospheric sciences since the pioneer applications in turbulence studies. If one decides to apply the wavelet analysis to a given signal, it is worthwhile to assess the actual need of the technique itself and the best way to perform it. In atmospheric signal applications, two main directions have been followed: the singularity and the variance analysis. In this paper the potential uses of this tool supported by some recently published works in the field of atmospheric sciences are discussed. Therefore, initially the characteristics and main properties of the wavelet analysis are presented, focusing on those that are mostly used in the analysis of atmospheric signals. Continuous and discrete wavelet transforms are also discussed, as well as the scalograms and the variance analysis. Finally some examples of wavelet analysis applied to a wide range of atmospheric science phenomena are presented.

When the interplanetary magnetic field carried by the solar wind opposes to the Earth's 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 be settled down. Wavelet analysis is becoming a common tool since they allow the decomposition of data, functions or operators into different frequency or scale components. Accordingly, wavelet transforms seem to be good tools to "zoom in" 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 magnetic field is explored. Magnetograms obtained at five magnetic stations for two geomagnetic storms have been analyzed by a Daubechies orthogonal wavelet transform decomposition. 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 just using non-processed data.

No abstract

No abstract

No abstract