Papers by Angelo De Santis
Annals of Geophysics
The present geomagnetic field is chaotic and ergodic: chaotic because it can no longer be predict... more The present geomagnetic field is chaotic and ergodic: chaotic because it can no longer be predicted beyond around 6 years; and ergodic in the sense that time averages correspond to phase-space averages. These properties have already been deduced from complex analyses of observatory time series in a reconstructed phase space and from global predicted and definitive models of differences in the time domain. These results imply that there is a strong necessity to make repeat-station magnetic surveys more frequently than every 5 years. This, in turn, will also improve the geomagnetic field secular variation models. This report provides practical examples and case studies.
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Proceedings of the II PAN AMERICAN WORKSHOP ON GEOMAGNETISM – II PANGEO, 2018
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Time series of geomagnetic field intensity data have been analyzed aiming to discover geomagnetic... more Time series of geomagnetic field intensity data have been analyzed aiming to discover geomagnetic variations’ local anomalies caused by tectonic activity of the region. The points of magnetic observations are located on AshotskJavakhk area of Armenian volcanic upland. The Earth’s crust of this territory is composed of different ages volcanic rocks of Neogen-Quaternary period as andesitic-dacites, andesites, dacites, andesitic-basalts distinguished by high values of magnetic susceptibility and remnant magnetization. Territory is broken by Basoum-Sevan, Javakhk and Yeghnakh deep faults.
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Annals of Geophysics, 1997
Models of the geomagnetic field are mathematical expressions able to represent the Earth's ma... more Models of the geomagnetic field are mathematical expressions able to represent the Earth's magnetic field space and time variations. Time variations on the long term basis are represented by the so-called secular variation. This paper describes and reviews recent activities of the Italian group at the Istituto Nazionale di Geofisica in regional magnetic field modelling. The models are introduced starting from the classical technique of Spherical Harmonic Analysis (SHA) undertaken for the first time by Gauss, the polynomial analysis and the regional harmonic analysis, specifically introduced as a regional analogue of SHA. In this last group the recent techniques of Spherical Cap Harmonic Analysis (SCHA), Translated Origin Spherical Cap Analysis (TOSCA) and Adjusted Spherical Cap Harmonic Analysis (ASHA) are also described and discussed.
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Annals of Geophysics, 2010
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Remote Sensing, 2020
The first 5.3 years of magnetic data from three Swarm satellites have been systematically analyze... more The first 5.3 years of magnetic data from three Swarm satellites have been systematically analyzed, and possible co-seismic magnetic disturbances in the ionosphere were investigated just a few minutes after the occurrence of large earthquakes. We preferred to limit the investigation to a subset of earthquakes selected in function of depth and magnitude. After a systematic inspection of the available data around (in time and space) the seismic events, we found 12 Swarm satellite tracks with co-seismic disturbances possibly produced by ten earthquakes from Mw5.6 to Mw6.9. The distance of the satellite to the earthquake epicenter corresponds to the measured distance-time arrival of the disturbance from the surface to the ionosphere, confirming that the identified disturbances are most likely produced by the seismic events. Secondly, we found a good agreement with a model that combined a propagation of the disturbance to the F2 ionospheric layer with an acoustic gravity wave at a veloci...
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Atmosphere, 2019
We analyse Swarm satellite magnetic field and electron density data one month before and one mont... more We analyse Swarm satellite magnetic field and electron density data one month before and one month after 12 strong earthquakes that have occurred in the first 2.5 years of Swarm satellite mission lifetime in the Mediterranean region (magnitude M6.1+) or in the rest of the world (M6.7+). The search for anomalies was limited to the area centred at each earthquake epicentre and bounded by a circle that scales with magnitude according to the Dobrovolsky’s radius. We define the magnetic and electron density anomalies statistically in terms of specific thresholds with respect to the same statistical quantity along the whole residual satellite track (|geomagnetic latitude| ≤ 50°, quiet geomagnetic conditions). Once normalized by the analysed satellite tracks, the anomalies associated to all earthquakes resemble a linear dependence with earthquake magnitude, so supporting the statistical correlation with earthquakes and excluding a relationship by chance.
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The recently proposed Antarctic geomagnetic Reference Model (ARM) is now available online. The mo... more The recently proposed Antarctic geomagnetic Reference Model (ARM) is now available online. The model, developed applying Spherical Cap Harmonic Analysis, is capable of synthesizing the main field and its secular variation over Antarctica, and was based on the annual means of X, Y, and Z components recorded by Antarctic Observatories during the last forty years as well as on a selected subset of Oersted satellite total field values measured in periods characterized by very low magnetic activity between December 1999 and January 2000. ARM presents a clear improvement with respect to the IGRF2000 model when representing the field and, especially, its secular variation, so it would be recommended the use of ARM when magnetic surveys in Antarctica, carried out at different times, are reduced to the same epoch. To facilitate the work to the scientific community involved on the study of Antarctic magnetic features like the anomaly field, ARM is accessible through the homepage of the Italia...
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Few days before many earthquakes a general change in the ratio of vertical to horizontal magnetic... more Few days before many earthquakes a general change in the ratio of vertical to horizontal magnetic field components in the ULF band, often called "polarization", has been observed that can be considered as a magnetic precursor of the subsequent earthquake. To explain such a specific behavior, we propose a simple model based on a linear current approximation depending on some assumption on the signal to noise ratio. This model is confirmed through a comparison that has been carried out between the experimental magnetic field data at Matsushiro (Japan, 1998.06.30, M=4.7) and Simeiz (Crimea, Ukraine, 1998.10.16, M=4.3 and 1998.10.18, M=4.3) earthquakes. About 1 - 2 days before these events we had recorded the anomalous decrease of the ratio of vertical to horizontal magnetic field components in Pc4 - Pc3 band. The NE-SW direction of the corresponding current linear model well agrees with the main tectonic feature of both seismogenic events. Additionally we also estimate the si...
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SEAFLOOR OBSERVATORIES, 2015
ABSTRACT by means of seafloor observatories extend the exploration and improve knowledge of our p... more ABSTRACT by means of seafloor observatories extend the exploration and improve knowledge of our planet? The ocean covers 70% of the planetary surface area, and yet we call our planet “Earth” and not − maybe more appropriately − “Ocean”. The ocean exerts a pervasive influence on the Earth’s environment but its nature is poorly understood. Developing a deep understanding of the ocean’s role and elucidating the complex physical, biological, chemical, and geological processes operating therein represent a major challenge in the opening decades of the 21st century. Major questions face us concerning the quality of human life and the destiny of biodiversity in such a rapidly changing environment that makes the ocean the last frontier of our planetary understanding. The establishment of a global network of ocean observatories to monitor the sub-seafloor, seafloor, and water column has been providing powerful insights into complex processes such as the geo-, bio- and hydrosphere interactions and their evolution and variability through time. However, there is still a long way to go before a comprehensive vision of processes in the oceans is reached. The importance of developing a global underwater network was initially recognized within the geophysical community, in particular by seismologists and geomagneticians in the mid-1980s when innovative methodologies for studies of the Earth’s interior came up against the impossibility of having an even coverage of planetary observations. Many international projects and initiatives have been carried out since the early 1990s to match this new need expressed by the scientific community. These projects have comprised experiments to validate long-term monitoring systems in very different environmental conditions: from shallow water to the deep sea, from coastal areas to open oceans, from temperate to polar latitudes. Since 1978, Japan has been the pioneer nation in managing cabled, and thus permanent, seafloor observatories driven by the need of limiting the damage of earthquakes and tsunamis to the social-economic fabric of the country. Sub-seafloor, seafloor, and water column Observatory Science is now a new branch of Earth (and Ocean) Sciences
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ABSTRACT The aim of this poster is to show the logic steps that start from the download of satell... more ABSTRACT The aim of this poster is to show the logic steps that start from the download of satellite data, then go to selection, validation and verification of data and, finally, produce an ensemble of models through appropriate data inversion. Last, but not least, step is the choice of the final model, through selection and validation of the best model by means of comparison with previous models, data not used for modelling, and expected statistical properties. To put in practice the above mentioned, we show the case of a construction of an European model for both main and anomaly Earth magnetic fields.
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Concepts of information theory are applied to global models of the main geomagnetic field of the ... more Concepts of information theory are applied to global models of the main geomagnetic field of the last century. Temporal behaviour of information content suggests that the field is in a chaotic state with characteristic times close to those of its westward drift and of the convective overturn in the outer core. In addition, we see that the secular variation shows
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Antarctica, 2006
ABSTRACT Some of the most interesting features of the Earth's magnetic field and of its t... more ABSTRACT Some of the most interesting features of the Earth's magnetic field and of its time variations are displayed in polar areas, where the geomagnetic field dipole poles are located. Space time models of the geomagnetic field give a mathematical description that allows generally to undertake a common epoch time reduction of magnetic surveys and to extract magnetic anomaly maps after removing the main part of the geomagnetic field; in addition in polar regions geomagnetic field models allow to follow the location of the geomagnetic dip poles in their time wandering. In this work the development of a dedicated regional magnetic reference model for Antarctica (Antarctic Reference Model, ARM) is presented and compared to the well known IGRF (International Geomagnetic Reference Field) model and it is shown that the first is more appropriate to better study the behaviour of secular variation and its unusual characteristics as observed in Antarctica. Moreover single and multi-station analyses have been applied to the longest available time series of geomagnetic data for Antarctica in order to investigate the most interesting behaviour of secular variation: the geomagnetic jerks. It was found that geomagnetic jerks are also detectable in Antarctica and that they show a peculiar space time structure.
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Tectonophysics, 2013
ABSTRACT The Antarctic Reference Model (ARM) has been here updated using recent geomagnetic data ... more ABSTRACT 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.
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NATO Security through Science Series
This paper presents the situation of the geomagnetic measurements over Albanian territory, distin... more 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 ...
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Annales Geophysicae, 1992
The K index indicates the level of magnetic perturbation with respect to the normal diurnal varia... more The K index indicates the level of magnetic perturbation with respect to the normal diurnal variation. Usually K is taken manually from magnetograms, and the involved operations are consequently rather subjective. When data are available in digital form, it is possible to derive the K index automatically, using computer algorithms. This work applies a new combined technique based on both fractal and harmonic analyses. While the latter is often used in K determination, the former provides a substantially novel approach. One year (1989) of K observations at L'Aquila observatory has been used as a basis for comparison between hand and computer estimations of K. Agreements which have been found are comparable with those expected from two different operators.
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Physics of the Earth and Planetary Interiors, 1991
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Papers by Angelo De Santis