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Geomagnetic jerks as chaotic fluctuations of the Earth’s magnetic field

Thu, 11 Apr 2013 22:00:00 GMT

Title: Geomagnetic jerks as chaotic fluctuations of the Earth’s magnetic field Authors: 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 Abstract: 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.

Geomagnetic jerks characterization via spectral analysis

Mon, 30 Apr 2012 22:00:00 GMT

Title: Geomagnetic jerks characterization via spectral analysis Authors: 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 Abstract: 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.

Paleomagnetic secular variation at the Azores during the last 3 ka

Wed, 11 Jul 2012 22:00:00 GMT

Title: Paleomagnetic secular variation at the Azores during the last 3 ka Authors: Di Chiara, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Speranza, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Porreca, M.; Centro de Vulcanologia e Avaliação de Riscos Geológicos, Universidade dos Açores, Ponta Delgada, Portugal. Abstract: We report on 33 new paleomagnetic directions obtained from 16 lava flows emplaced in the last 3 ka on São Miguel, the largest island of the Azores. The data provide 27 well-dated directions from historical or 14C dated flows which, together with 6 directions previously gathered from the same flows by Johnson et al. (1998), yield the first paleomagnetic directional record of the last 3 ka from the Atlantic Ocean. Within-flow directions are consistent, suggesting that inclination swings from 60 to 25 and declination changes between 10 to 20 reflect variations in the geomagnetic field over the last 3 ka. To a first approximation, the declination record is consistent with predictions from CALS3k.4 and gufm1 global field models. Conversely, inclination values are lower than model predictions at two different ages: 1) four sites from the 1652 AD flow yield I = 48 instead of I = 63 predicted by gufm1; 2) data from several flows nicely mimic the inclination minimum of 800–1400 AD, but inclination values are lower by 10 than CALS3k.4 model predictions. By interpolating a cubic spline fit on declination / inclination versus age data, we tentatively infer the directional evolution of the geomagnetic field at the Azores from 1000 BC to 1600 AD. The obtained curve shows three tracks in virtual overlap during the 1000–800 BC, 800–500 BC, and 400–700 AD time spans.

Correlation of welded ignimbrites on Pantelleria (Strait of Sicily) using paleomagnetism

Wed, 29 Feb 2012 23:00:00 GMT

Title: Correlation of welded ignimbrites on Pantelleria (Strait of Sicily) using paleomagnetism Authors: Speranza, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Di Chiara, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Rotolo, S. G.; Dipartimento di Scienze della Terra e del Mare (DISTeM), Università di Palermo, Via Archirafi 36, 90123 Palermo, Italy Abstract: Although the oldest volcanic rocks exposed at Pantelleria (Strait of Sicily) are older than 300 ka, most of the island is covered by the 45–50 ka Green Tuff ignimbrite, thought to be related to the Cinque Denti caldera, and younger lavas and scoria cones. Pre-50 ka rocks (predominantly rheomorphic ignimbrites) are exposed at isolated sea cliffs, and their stratigraphy and chronology are not completely resolved. Based on volcanic stratigraphy and K/Ar dating, it has been proposed that the older La Vecchia caldera is related to ignimbrite Q (114 ka), and that ignimbrites F, D, and Z (106, 94, and 79 ka, respectively) were erupted after caldera formation. We report here the paleomagnetic directions obtained from 23 sites in ignimbrite P (133 ka) and four younger ignimbrites, and from an uncorrelated (and loosely dated) welded lithic breccia thought to record a caldera-forming eruption. The paleosecular variation of the geomagnetic field recorded by ignimbrites is used as correlative tool, with an estimated time resolution in the order of 100 years. We find that ignimbrites D and Z correspond, in good agreement with recent Ar/Ar ages constraining the D/Z eruption to 87 ka. The welded lithic breccia correlates with a thinner breccia lying just below ignimbrite P at another locality, implying that collapse of the La Vecchia caldera took place at ~130–160 ka. This caldera was subsequently buried by ignimbrites P, Q, F, and D/Z. Paleomagnetic data also show that the northern caldera margin underwent a ~10° west–northwest (outwards) tilting after emplacement of ignimbrite P, possibly recording magma resurgence in the crust.

The contribution of L'Aquila (Italy) Geomagnetic Observatory to MAGDAS project

Fri, 30 Sep 2011 22:00:00 GMT

Title: The contribution of L'Aquila (Italy) Geomagnetic Observatory to MAGDAS project Authors: Lepidi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Meloni, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Palangio, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Yumoto, K.; Space Environment Research Center, Kyushu University Abstract: The geomagnetic Observatory of L'Aquila (Italy) was founded by Istituto Nazionale di Geofisica e Vulcanologia (INGV) in 1958, on the occasion of the International Geophysical Year. It is the main Italian geomagnetic observatory. Since 1999 L'Aquila Observatory belongs to the Intermagnet system, an International network grouping worldwide geomagnetic observatories able to provide Earth's magnetic field measurements according to precise quality standards. Geomagnetic field measurements in L'Aquila are used to study the variations of the Earth's geomagnetic field, both of internal and external origin. In November 2008 a new magnetometer was installed in L'Aquila within the MAGDAS project, coordinated by SERC. The location of this installation can be useful to complete the MAGDAS monitoring system to study solar-terrestrial events.

A Holocene paleosecular variation record from the northwestern Barents Sea continental margin

Mon, 31 Oct 2011 23:00:00 GMT

Title: A Holocene paleosecular variation record from the northwestern Barents Sea continental margin Authors: Sagnotti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Macrì, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Lucchi, R.; Istituto Nazionale di Oceanografia e Geofisica Sperimentale, Borgo Grotta Gigante 42/c, Sgonico, Trieste I‐34010, Italy; Rebesco, M.; Istituto Nazionale di Oceanografia e Geofisica Sperimentale, Borgo Grotta Gigante 42/c, Sgonico, Trieste I‐34010, Italy; Camerlenghi, A.; Istitució Catalana de Recerca i Estudis Avançats, E‐08028 Barcelona, Spain Abstract: A high‐resolution paleomagnetic and rock magnetic study has been carried out on sediment cores collected in glaciomarine silty‐clay sequences from the continental shelf and slope of the southern Storfjorden trough‐mouth fan, on the northwestern Barents Sea continental margin. The Storfjorden sedimentary system was investigated during the SVAIS and EGLACOM cruises, when 10 gravity cores, with a variable length from 1.03 m to 6.41 m, were retrieved. Accelerator mass spectrometry (AMS) 14C analyses on 24 samples indicate that the cores span a time interval that includes the Holocene, the last deglaciation phase and in some cores the last glacial maximum. The sediments carry a well‐defined characteristic remanent magnetization and have a valuable potential to reconstruct the paleosecular variation (PSV) of the geomagnetic field, including relative paleointensity (RPI) variations. The paleomagnetic data allow reconstruction of past dynamics and amplitude of the geomagnetic field variations at high northern latitudes (75°–76° N). At the same time, the rock magnetic and paleomagnetic data allow a high‐resolution correlation of the sedimentary sequences and a refinement of their preliminary age models. The Holocene PSV and RPI records appear particularly sound, since they are consistent between cores and they can be correlated to the closest regional stacking curves (UK PSV, FENNOSTACK and FENNORPIS) and global geomagnetic model for the last 7 ka (CALS7k.2). The computed amplitude of secular variation is lower than that outlined by some geomagnetic field models, suggesting that it has been almost independent from latitude during the Holocene.

Daily variation characteristics at polar geomagnetic observatories

Tue, 02 Aug 2011 22:00:00 GMT

Title: Daily variation characteristics at polar geomagnetic observatories Authors: Lepidi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cafarella, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pietrolungo, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Di Mauro, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: This paper is based on the statistical analysis of the diurnal variation as observed at six polar geomagnetic observatories, three in the Northern and three in the Southern hemisphere. Data are for 2006, a year of low geomagnetic activity. We compared the Italian observatory Mario Zucchelli Station (TNB; corrected geomagnetic latitude: 80.0 S), the French–Italian observatory Dome C (DMC; 88.9 S), the French observatory Dumont D’Urville (DRV; 80.4 S) and the three Canadian observatories, Resolute Bay (RES; 83.0 N), Cambridge Bay (CBB; 77.0 N) and Alert (ALE, 87.2 N). The aim of this work was to highlight analogies and differences in daily variation as observed at the different observatories during low geomagnetic activity year, also considering Interplanetary Magnetic Field conditions and geomagnetic indices.

A re-evaluation of the Italian historical geomagnetic catalogue: implications for paleomagnetic dating at active Italian volcanoes

Wed, 08 Jun 2011 22:00:00 GMT

Title: A re-evaluation of the Italian historical geomagnetic catalogue: implications for paleomagnetic dating at active Italian volcanoes Authors: D'Ajello Caracciolo, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pignatelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Speranza, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Meloni, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: Paleomagnetism is proving to represent one of the most powerful dating tools of volcanics emplaced in Italy during the last few centuries/millennia. This method requires that valuable proxies of the local geomagnetic field (paleo) secular variation ((P)SV) are available. To this end, we re-evaluate the whole Italian geomagnetic directional dataset, consisting of 833 and 696 declination and inclination measurements, respectively, carried out since 1640AD at several localities. All directions were relocated via the virtual geomagnetic pole method to Stromboli (38.8 N, 15.2 E), the rough centre of the active Italian volcanoes. For declinationonly measurements, missing inclinations were derived (always by pole method) by French data (for period 1670– 1789), and by nearby Italian sites/years (for periods 1640– 1657 and 1790–1962). Using post-1825 declination values, we obtain a 0.46±0.19 yr−1 westward drift of the geomagnetic field for Italy. The original observation years were modified, considering such drift value, to derive at a driftcorrected relocated dataset. Both datasets were found to be in substantial agreement with directions derived from the field models by Jackson et al. (2000) and Pavon-Carrasco et al. (2009). However, the drift-corrected dataset minimizes the differences between the Italian data and both field models, and eliminates a persistent 1.6 shift of 1933–1962 declination values from Castellaccio with respect to other nearly coeval Italian data. The relocated datasets were used to calculate two post-1640 Italian SV curves, with mean directions calculated every 30 and 10 years before and after 1790, respectively. The curve comparison suggests that both available field models yield the best available SV curve to perform paleomagnetic dating of 1600–1800AD Italian volcanics, while the Italian drift-corrected curve is probably preferable for the 19th century. For the 20th century, the global model by Jackson et al. (2000) yields more accurate inclination values, while the declinations from our drift-corrected curve seem to better represent the local field evolution, at least for the first half of the century.

Azimuthal propagation of Pc5 geomagnetic field pulsations in the southern polar cap

Mon, 14 Mar 2011 23:00:00 GMT

Title: Azimuthal propagation of Pc5 geomagnetic field pulsations in the southern polar cap Authors: Lepidi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Cafarella, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Pietrolungo, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Santarelli, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia Abstract: A statistical analysis of low frequency geomagnetic fluctuations at the two Antarctic stations Mario Zucchelli Station (geographic coordinates: 74.7 S, 164.1 E; corrected geomagnetic coordinates: 80.0 S, 306.8 E) and Dumont D’Urville (geographic coordinates: 66.7 S, 140.0 E; corrected geomagnetic coordinates: 80.4 S, 236.0 E) is shown. The analysis focuses on power spectra, coherence and phase difference between the stations, which are both located in the polar cap, with a 5-h magnetic local time displacement along a geomagnetic parallel; in this situation, the phase difference between geomagnetic fluctuations indicates the direction of their azimuthal propagation. Coherent fluctuations have been found to occur preferably when both stations are on the same side (dawnward or duskward) with respect to the polar cusp; moreover, around local magnetic midnight, they occur essentially during open magnetospheric conditions. The phase difference for coherent fluctuations indicates a propagation direction away from local geomagnetic noon and midnight. Also the analysis of three individual pulsation events, occurring at different times during the day, is shown; they are characterized at the two stations by simultaneous, coherent fluctuations, whose phase difference finds correspondence with the statistical behaviour. 2010 COSPAR. Published by Elsevier Ltd. All rights reserved.

A continuous palaeosecular variation record of the last four millennia from the Augusta Bay (Sicily, Italy)

Fri, 31 Dec 2010 23:00:00 GMT

Title: A continuous palaeosecular variation record of the last four millennia from the Augusta Bay (Sicily, Italy) Authors: Sagnotti, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Smedile, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; De Martini, P. M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Pantosti, D.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; Speranza, F.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Winkler, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia; Del Carlo, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione di Pisa, Via della Faggiola 32, 56126 Pisa, Italy; Bellucci, L. G.; Istituto di Scienze Marine, CNR, Sede di Bologna – Geologia Marina, Via P. Gobetti 101, 40129 Bologna, Italy; Gasperini, L.; Istituto di Scienze Marine, CNR, Sede di Bologna – Geologia Marina, Via P. Gobetti 101, 40129 Bologna, Italy Abstract: We present a high-resolution palaeomagnetic and rock magnetic study of two cores, MS06 and MS06-SW (6.7 and 1.1 m long, respectively), collected at 72 m below sea level in the Augusta Bay shelf (Eastern Sicily, Ionian Sea, Italy) about 2.3 kmfrom the coastline. Geophysical surveying carried out in the sampling area highlighted the presence of a homogeneous sedimentary sequence that most likely was deposited after the Last Glacial Maximum and was not affected by anthropogenic disturbances. The two cores penetrated a monotonous mud sedimentary sequence, interrupted at ∼3 m depth by a 3–4-cm-thick volcanic sandy layer that is correlated with the tephra fallout deposit produced by the 122 BC plinian eruption of Mt Etna. This tephra, along with radiocarbon dating of nine marine shells and with radioactive tracers for the uppermost 0.3 m (210Pb and 137Cs), provide the chronological constraints for the stratigraphic sequence that resulted younger than 4500 yr BP. Palaeomagnetic and rock magnetic data show that the sample sequence is magnetically homogeneous. A single peak of high magnetic mineral concentration is present and corresponds to the volcanic sandy layer. Palaeomagnetic data allowed the identification of a well-defined characteristic remanent magnetization that provides a high-resolution record of palaeosecular variation (PSV) at the sampling site. The reconstructed PSV curve is in good agreement with the available regional reference PSV curves and with the prediction from recent PSV modelling for Europe. The palaeomagnetic data obtained in this study on the one hand support and refine the age model for the cores, derived from other independent constraints, and on the other hand provide an original high-resolution PSV curve that can serve as a reference for the central Mediterranean over the last 4 ka.