Deep seafloor magnetic observations under GEOSTAR project

Performing good quality magnetic observations is not an easy task; making them in the extreme marine environment is even much more challenging. The European funded GEOSTAR project succeeded in reaching this difficult goal. After the shallow seawater test experiment performed in the Adriatic sea in 1998, the main aims of the GEOSTAR project were achieved two years later during the six-month deep seafloor mission in the Tyrrhenian sea at around 2 km depth. Details and results about the shallow seawater mission in the Adriatic sea were published in previous articles; this paper is concerned with the deep seafloor mission in the Tyrrhenian sea close to Ustica Island and presents some results related to the geomagnetic recordings

Two geomagnetic regional models for Albania and south-east Italy from 1990 to 2010 with prediction to 2012 and comparison with IGRF-11

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

ITalian Geomagnetic Reference Field (ITGRF): update for 2000 and secular variation model up to 2005 by autoregressive forecasting

The updated version of the ITalian Geomagnetic Reference Field (ITGRF) for 2000.0 and its secular variation model up to 2005.0 are presented in this paper. The main field model is based on a simple polynomial approximation in latitude and longitude of the geomagnetic field elements computed from IGRF on a 12° ¥ 11° grid centred over Italy. The annual means from L'Aquila observatory were used to determine the baseline level, imposing a constant observatory anomaly bias. This procedure gives a set of 6 coefficients every 5 years from 1960 to 2005 for the horizontal H, total field F, vertical Z and declination D elements of the geomagnetic field. The extrapolation of ITGRF to 2005 is based on an autoregressive forecasting of the L'Aquila observatory annual means. Comparison of the field values computed from the model with those recorded at the other Italian observatory (Castello Tesino) shows that the ITGRF improves the fit of the secular variation pattern with respect to the global IGRF model by a factor of 3. The ITGRF represents a reliable alternative to global models when reducing magnetic surveys to a common reference epoch over the Italian region

A geomagnetic reference model for Albania, Southern Italy and the Ionian Sea from 1990 to 2005

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

Deep seafloor magnetic observations under GEOSTAR project

n/

ITalian Geomagnetic Reference Field (ITGRF): update for 2000 and secular variation model up to 2005 by autoregressive forecasting

The updated version of the ITalian Geomagnetic Reference Field (ITGRF) for 2000.0 and its secular variation model up to 2005.0 are presented in this paper. The main field model is based on a simple polynomial approximation in latitude and longitude of the geomagnetic field elements computed from IGRF on a 12° ¥ 11° grid centred over Italy. The annual means from L'Aquila observatory were used to determine the baseline level, imposing a constant observatory anomaly bias. This procedure gives a set of 6 coefficients every 5 years from 1960 to 2005 for the horizontal H, total field F, vertical Z and declination D elements of the geomagnetic field. The extrapolation of ITGRF to 2005 is based on an autoregressive forecasting of the L'Aquila observatory annual means. Comparison of the field values computed from the model with those recorded at the other Italian observatory (Castello Tesino) shows that the ITGRF improves the fit of the secular variation pattern with respect to the global IGRF model by a factor of 3. The ITGRF represents a reliable alternative to global models when reducing magnetic surveys to a common reference epoch over the Italian region

Antarctic geomagnetic reference model updated to 2010 and provisionally to 2012

The Antarctic Reference Model (ARM) has been here updated using recent geomagnetic data measured over the Antarctic continent from both ground observatories and satellites. This regional geomagnetic model is based on a Spherical Cap Harmonic Analysis (SCHA) of geomagnetic field measurements over a polar cap of 30° half-angle centred at the geographic South Pole, fixing the maximum spatial expansion index kmax=8 and the maximum temporal order of polynomials qmax=4. The importance of updating ARM model lies, for instance, in its usefulness for the reduction of magnetic surveys, performed during the period of model validity over the Antarctica, or for geomagnetic anomaly field estimations. Moreover, so far, ARM still remains the only regional reference magnetic model specifically constructed for the Antarctic continent. The present updated version can be considered valid from 1955.5 to 2010.0 with predictive coefficients up to 2012.0. The model includes the most recent available data but, in contrast to previous versions not only does it take advantage of a stricter selection of satellite data in order to consider even quieter periods of external magnetic activity, but it also includes ground observatory data previous to 1960 going back to 1955.8. Like the previous versions, the new updated model has been tested and compared with major global models to show its reliability over the region under investigation

Information content and K-entropy of the present geomagnetic field

Concepts of information theory are applied to global models of the geomagnetic field B of the last century. The temporal behavior of information content suggests that B is in a chaotic state with characteristic times close to those of its westward drift and of the convective overturn in the outer core and the secular variation shows a comparable characteristic time of predictability. The main implication of these results is the suggestive hypothesis that a possible geomagnetic reversal or excursion is currently in progress

Antarctic geomagnetic reference model updated to 2010 and provisionally to 2012

The Antarctic Reference Model (ARM) has been here updated using recent geomagnetic data measured over the Antarctic continent from both ground observatories and satellites. This regional geomagnetic model is based on a Spherical Cap Harmonic Analysis (SCHA) of geomagnetic field measurements over a polar cap of 30° half-angle centred at the geographic South Pole, fixing the maximum spatial expansion index kmax=8 and the maximum temporal order of polynomials qmax=4. The importance of updating ARM model lies, for instance, in its usefulness for the reduction of magnetic surveys, performed during the period of model validity over the Antarctica, or for geomagnetic anomaly field estimations. Moreover, so far, ARM still remains the only regional reference magnetic model specifically constructed for the Antarctic continent. The present updated version can be considered valid from 1955.5 to 2010.0 with predictive coefficients up to 2012.0. The model includes the most recent available data but, in contrast to previous versions not only does it take advantage of a stricter selection of satellite data in order to consider even quieter periods of external magnetic activity, but it also includes ground observatory data previous to 1960 going back to 1955.8. Like the previous versions, the new updated model has been tested and compared with major global models to show its reliability over the region under investigation.Published13-253.4. GeomagnetismoJCR Journalreserve