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[1] The geomagnetic field is chaotic and can be characterized by a mean exponential time scale < t > after which it is no longer predictable. It is also ergodic, so time analyses can substitute the more difficult phase space analyses. Taking advantage of these two properties of the Earth's magnetic field, a scheme of processing global geomagnetic models in time is presented, to estimate fluctuations of the time scale t. Here considering that the capability to predict the geomagnetic field is reduced over periods of geomagnetic jerks, we propose a method to detect these events over a long time span. This approach considers that epochs characterized by relative minima of fluctuations in time scale t, i.e., those periods when a geomagnetic field is less predictable, are possible jerk occurrence dates. We analyze the last 400 years of the geomagnetic field (covered by the Gufm1 model) to detect minima of fluctuations, i.e., epochs characterized by low values of the time scale. Most of the well known jerks are confirmed through this method and a few others have been suggested. Finally, we also identify some short periods when the field is less chaotic (more predictable) than usual, naming these periods as steady state geomagnetic regime, to underline their opposite behavior with respect to jerks.

Here we present a revised geomagnetic reference model for the region comprising Albanian territory, southeast part of Italian Peninsula and Ionian Sea from 1990 to 2010 with prediction to 2012. This study is based on the datasets of magnetic measurements taken during different campaigns in Albania and Italy in the time of concern, together with a total intensity data set from the Ørsted and CHAMP satellite missions. The model is designed to represent the Cartesian components, X , Y , Z and the total intensity F of the main geomagnetic field (and its secular variation SV) for the period of interest. To develop the model, we applied a Spherical Cap Harmonic Analysis (SCHA) of the geomagnetic potential over a 16 • cap with most of the observations concentrated in the central 4 • half-angle. The use of a larger cap than that containing the data was made to reduce the typical problems in SV modelling over small regions. Also a new technique, called "Radially Simplified Spherical Cap Harmonic Analysis" (RS-SCHA), was developed to improve the model especially in the radial variation of the geomagnetic field components. Both these models provide an optimal representation of the geomagnetic field in the considered region compared with the International Geomagnetic Reference Field model (IGRF-11) and can be used as reference models to reduce magnetic surveys undertaken in the area during the time of validity of the model, or to extrapolate the field till 2012.

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In this study we have applied spectral techniques to analyze geomagnetic field time-series provided by observatories, and compared the results with those obtained from analogous analyses of synthetic data estimated from models. Then, an algorithm is here proposed to detect the geomagnetic jerks in time-series, mainly occurring in the eastern component of the geomagnetic field. Applying such analysis to time-series generated from global models has allowed us to depict the most important space-time features of the geomagnetic jerks all over the globe, since the beginning of XXth century. Finally, the spherical harmonic power spectrum of the third derivative of the main geomagnetic field has been computed from 1960 to 2002.5, bringing new insights to understand the spatial evolution of these rapid changes of the geomagnetic field