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Department of Physics, Faculty of Natural Sciences, University of Tirana, Albania
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- PublicationOpen AccessA geomagnetic reference model for Albania, Southern Italy and the Ionian Sea from 1990 to 2005(2004)
; ; ; ; ; ; ;Duka, B.; Department of Physics, Faculty of Natural Sciences, University of Tirana, Albania ;Gaya-Piqué, L. R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Bushati, S.; Academy of Sciences of Albania, Tirana, Albania ;Chiappini, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Dominici, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; ; ; ; ; Taking advantage of the measurements undertaken during the Albanian and Italian magnetic repeat station networks since 1990, as well as of a selected set of Ørsted satellite total field measurements, a magnetic reference model for the region comprising the Albanian territory, the southern part of the Italian Peninsula, and the Ionian Sea is presented. The model, designed to model the components of the main geomagnetic field for epochs between 1990 and 2005, has been developed by means of spherical cap harmonic analysis applied to a cap of semiangle 8°, larger than that investigated to take into account the appropriate spatial wavelength content of the main geomagnetic field over the region. The goodness of the fit to the real data suggests that the model can be used as a reference model to reduce magnetic surveys developed in the area during the time of validity of the model.288 179 - PublicationRestrictedGeomagnetic jerks as chaotic fluctuations of the Earth’s magnetic field(2013-04-12)
; ; ; ; ; ; ;Qamili, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Isac, A.; Geological Institute of Romania, Bucharest, Romania ;Mandea, M.; Centre National d’Etudes Spatiales, Paris, France ;Duka, B.; Faculty of Natural Sciences, University of Tirana, Tirana, Albania ;Simonyan, A.; Institute of Geophysics, Academy of Science, Yerevan, Armenia; ; ; ; ; The geomagnetic field is chaotic and can be characterized by a mean exponential time scaleafter 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.319 39 - PublicationOpen AccessTwo geomagnetic regional models for Albania and south-east Italy from 1990 to 2010 with prediction to 2012 and comparison with IGRF-11(2010)
; ; ; ; ; ; ; ;Qamili, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Cianchini, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Duka, B.; Department of Physics, Faculty of Natural Sciences, University of Tirana, Albania ;Gaya-Piqué, L. R.; On-Site Inspection Division, Comprehensive Nuclear-Test Ban Treaty Organization PrepCom, Vienna, Austria ;Dominici, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Hyka, Niko; Department of Physics, Faculty of Natural Sciences, University of Tirana, Albania; ; ; ; ; ; Here we present a revised geomagnetic reference model for the region comprising Albanian territory, south-east 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) 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 2012.341 320 - PublicationOpen AccessComparison of different methods of analysis of satellite geomagnetic anomalies over Italy(1998-04)
; ;Duka, B.; Department of Physics, Faculty of Natural Sciences, University of Tirana, AlbaniaDifferent methods of analysis have been applied to satellite geomagnetic data that are claimed to be representative of the crustal geomagnetic field of the Italian area. The methods are compared with each other concluding that the SCHA is the best one. The downward continuation of the field by different methods gives different results, the most realistic are those of SCHA and RHA methods. Some remarks about each method and their results for the Italian area are presented.242 200 - PublicationOpen AccessGeomagnetic jerks characterization via spectral analysis(2012-05)
; ; ; ; ; ;Duka, B.; Faculty of Natural Sciences, University of Tirana, Tirana, Albania ;De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Mandea, M.; Centre National d’Etudes Spatiales, Paris, France ;Isac, A.; Geological Institute of Romania, Bucharest, Romania ;Qamili, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; ; ; ; 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.250 120 - PublicationRestrictedThe Albanian Geomagnetic Repeat Station Network at 1994.75(1997)
; ; ; ; ; ; ; ; ; ; ;A new national geomagnetic network of repeat stations for total field F, horizontal component H, vertical component Z and declination D has been established in a collaboration between the Albanian Geological Society (Center for Geochemistry and Geophysics), the Tirana University (Albania) and the Istituto Nazionale di Geofisica (Italy). From the observed magnetic field elements all repeat stations were referred to Epoch 1994.75 and normal reference fields were computed in the form of 1st order polynomials in latitude and longitude. An overview of all work, including a brief history of the Albanian magnetic measurements, magnetic survey results, normal fields and secular variation estimates is presented.243 5 - PublicationOpen AccessCrustal field recovery and secular variation from regional and global models over AlbaniaThe static geomagnetic field of crustal origin is optionally calculated bythe recent global geomagnetic field models. However, their description in global scale tends to miss some local characteristics. The same can be inferred for the rate of the geomagnetic field changes i.e. secular variation (SV). In order to depict some particularity of crustal field in local scale for small region like as Albania, two regional models are constructed: one based on the Legendre’s polynomials and the other based on a linear approximation. Both models use data from different measurement campaigns in the Albanian repeat stations and few data from neighbourhood countries. The residuals produced by these models and by the recent global models: EMM2015, POMME – 9 and CM5 are calculated and compared. The SV from regional and global models following standard procedures are also calculated. Substantial differences between SV calculated by global models and regional models are observed.
155 49 - PublicationOpen AccessA numerical experiment on the spherical harmonic analysis of core and crustal geomagnetic fields(1993)
; ;Duka, B.; Faculty of Natural Science,s, Department of Physics, University of Tirana, Albania152 183 - PublicationRestrictedUsing ‘‘domino’’ model to study the secular variation of the geomagnetic dipolar moment(2015-03-14)
; ; ; ; ;Duka, B.; Dept. of Physics, Faculty of Natural Sciences – University of Tirana, Albania ;Peqini, K.; Dept. of Physics, Faculty of Natural Sciences – University of Tirana, Albania ;De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Pavón-Carrasco, F. J.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; ; ; Aiming to understand the physical processes underneath the reversals events of geomagnetic field, different numerical models have been conceived. We considered here the so named ‘‘domino’’ model, an Ising–Heisenberg model of interacting magnetic macrospins aligned along a ring. This model was proposed by Mazaud and Laj (1989) and then applied by Mori et al. (2013) to study geomagnetic field reversals. The long series of the axial magnetic moment (dipolar moment or ‘‘magnetization’’) generated by the ‘‘domino’’ model are empirically studied by varying all model parameters. We present here some results which are slightly different from those given by Mori et al. (2013), and will provide our explanation on the presence of these differences. We also define the set of parameters that supply the longest mean time between reversals. Using this set of parameters, a large number of time series of axial magnetic moment are also generated. After de-noising the fluctuation of these time series and averaging them, we compared the resulting averaged series with the series of axial dipolar magnetic moment values supplied by CALS7k.2, and CALS10k.1b models, finding similar behavior for the all time series. In a similar way, we also compared the averaged 14,000 years long series of dipolar moment with the dipolar magnetic moment obtained by the model SHA.DIF.14k.279 97 - PublicationRestrictedOn the Modeling of a Geomagnetic Reference Field for the Balkan Region(2006)
; ; ; ;Duka, B.; Department of Physics, Faculty of Natural Sciences, University of Tirana, Albania ;De Santis, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia ;Gaya-Piqué, L. R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; ; ; ; ; ;Rasson, J. L.; Institut Royal Météorologique de Belgique, Dourbes, Belgium ;Delipetrov, T.; Department of Geology and Geophysics, Faculty of Mining and Geology, 2000 Štip, Macedonia; This paper presents the situation of the geomagnetic measurements over Albanian territory, distinguishing the campaigns of 1942.0, 1961.0, 1990.4, 1994.75 and 2004.7 epochs. The results of the latest model of the geomagnetic field for Southern Italy and Albanian territory are therefore shown. This model was created using SCHA (Spherical Cap Harmonic Analysis) technique, applied on all ground data from three different epochs (1990.4, 1994.5 and 2003.7) and a selected dataset from Oersted satellite mission. The ground data were confined in a small Spherical Cap that we expect to enlarge with ground data from adjoining countries in order to compose an accurate Balkan Geomagnetic Reference Field Model.170 26