@article{ZaourarHamoudiMandeaetal.2013,
  author    = {Zaourar, N. and Hamoudi, M. and Mandea, M. and Balasis, G. and Holschneider, Matthias},
  title     = {Wavelet-based multiscale analysis of geomagnetic disturbance},
  series = {EARTH PLANETS AND SPACE},
  volume    = {65},
  journal   = {EARTH PLANETS AND SPACE},
  number    = {12},
  publisher = {TERRA SCIENTIFIC PUBL CO},
  address   = {TOKYO},
  issn      = {1343-8832},
  doi       = {10.5047/eps.2013.05.001},
  pages     = {1525 -- 1540},
  year      = {2013},
  abstract  = {The dynamics of external contributions to the geomagnetic field is investigated by applying time-frequency methods to magnetic observatory data. Fractal models and multiscale analysis enable obtaining maximum quantitative information related to the short-term dynamics of the geomagnetic field activity. The stochastic properties of the horizontal component of the transient external field are determined by searching for scaling laws in the power spectra. The spectrum fits a power law with a scaling exponent beta, a typical characteristic of self-affine time-series. Local variations in the power-law exponent are investigated by applying wavelet analysis to the same time-series. These analyses highlight the self-affine properties of geomagnetic perturbations and their persistence. Moreover, they show that the main phases of sudden storm disturbances are uniquely characterized by a scaling exponent varying between 1 and 3, possibly related to the energy contained in the external field. These new findings suggest the existence of a long-range dependence, the scaling exponent being an efficient indicator of geomagnetic activity and singularity detection. These results show that by using magnetogram regularity to reflect the magnetosphere activity, a theoretical analysis of the external geomagnetic field based on local power-law exponents is possible.},
  language  = {en}
}
@article{ZaourarHamoudiHolschneideretal.2013,
  author    = {Zaourar, Naima and Hamoudi, Mohamed and Holschneider, Matthias and Mandea, Mioara},
  title     = {Fractal dynamics of geomagnetic storms},
  series = {Arabian journal of geosciences},
  volume    = {6},
  journal   = {Arabian journal of geosciences},
  number    = {6},
  publisher = {Springer},
  address   = {Heidelberg},
  issn      = {1866-7511},
  doi       = {10.1007/s12517-011-0487-0},
  pages     = {1693 -- 1702},
  year      = {2013},
  abstract  = {We explore fluctuations of the horizontal component of the Earth's magnetic field to identify scaling behaviour of the temporal variability in geomagnetic data recorded by the Intermagnet observatories during the solar cycle 23 (years 1996 to 2005). In this work, we use the remarkable ability of scaling wavelet exponents to highlight the singularities associated with discontinuities present in the magnetograms obtained at two magnetic observatories for six intense magnetic storms, including the sudden storm commencements of 14 July 2000, 29-31 October and 20-21 November 2003. In the active intervals that occurred during geomagnetic storms, we observe a rapid and unidirectional change in the spectral scaling exponent at the time of storm onset. The corresponding fractal features suggest that the dynamics of the whole time series is similar to that of a fractional Brownian motion. Our findings point to an evident relatively sudden change related to the emergence of persistency of the fractal power exponent fluctuations precedes an intense magnetic storm. These first results could be useful in the framework of extreme events prediction studies.},
  language  = {en}
}