The debated question on the possible relation between the Earth's magnetic field and climate has been usually focused on direct correlations between different time series representing both systems. ...However, the physical mechanism able to potentially explain this connection is still an open issue. Finding hints about how this connection could work would suppose an important advance in the search of an adequate physical mechanism. Here, we propose an innovative information-theoretic tool, i.e. the transfer entropy, as a good candidate for this scope because is able to determine, not simply the possible existence of a connection, but even the direction in which the link is produced. We have applied this new methodology to two real time series, the South Atlantic Anomaly (SAA) area extent at the Earth's surface (representing the geomagnetic field system) and the Global Sea Level (GSL) rise (for the climate system) for the last 300 years, to measure the possible information flow and sense between them. This connection was previously suggested considering only the long-term trend while now we study this possibility also in shorter scales. The new results seem to support this hypothesis, with more information transferred from the SAA to the GSL time series, with about 90% of confidence level. This result provides new clues on the existence of a link between the geomagnetic field and the Earth's climate in the past and on the physical mechanism involved because, thanks to the application of the transfer entropy, we have determined that the sense of the connection seems to go from the system that produces geomagnetic field to the climate system. Of course, the connection does not mean that the geomagnetic field is fully responsible for the climate changes, rather that it is an important driving component to the variations of the climate.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
The study of the preparation phase of large earthquakes is essential to understand the physical processes involved, and potentially useful also to develop a future reliable short-term warning system. ...Here we analyse electron density and magnetic field data measured by Swarm three-satellite constellation for 4.7 years, to look for possible in-situ ionospheric precursors of large earthquakes to study the interactions between the lithosphere and the above atmosphere and ionosphere, in what is called the Lithosphere-Atmosphere-Ionosphere Coupling (LAIC). We define these anomalies statistically in the whole space-time interval of interest and use a Worldwide Statistical Correlation (WSC) analysis through a superposed epoch approach to study the possible relation with the earthquakes. We find some clear concentrations of electron density and magnetic anomalies from more than two months to some days before the earthquake occurrences. Such anomaly clustering is, in general, statistically significant with respect to homogeneous random simulations, supporting a LAIC during the preparation phase of earthquakes. By investigating different earthquake magnitude ranges, not only do we confirm the well-known Rikitake empirical law between ionospheric anomaly precursor time and earthquake magnitude, but we also give more reliability to the seismic source origin for many of the identified anomalies.
A large earthquake of 7.8 magnitude occurred on 25 April 2015, 06:26 UTC, with the epicenter in Nepal. Here, taking advantage of measurements provided by the Swarm magnetic satellites, we investigate ...the possibility to detect some series of pre-earthquake magnetic anomalous signals, likely due to a lithosphere–atmosphere–ionosphere coupling, that can be a potential earthquake precursory pattern. Different techniques have been applied to Swarm data available during two months around earthquake occurrence. From the detected magnetic anomalies series (during night and magnetically quiet times or with an automatic detection algorithm), we show that the cumulative number of anomalies follows the same typical power-law behavior of a critical system approaching its critical time, and hence recovers as the typical recovery phase after a large event. The similarity of this behavior with the one obtained from seismic data analysis and the application of the analyses also to another period without significant seismicity do support a lithospheric-linked origin of the observed magnetic anomalies. We suggest that they might be connected to the preparation phase of the Nepal earthquake.
•Swarm magnetic data are analyzed in occasion of the large 2015 Nepal earthquake.•A statistical method is applied to detect earthquake related magnetic anomalies.•A temporal pattern of anomalies emerges as typical of critical systems.•The same pattern emerges from the seismic data.•This agreement suggests an internal origin of the found pattern.
•New geomagnetic field reconstruction (SHAWQ2k) has been obtained for the last 2 ka.•A novelty weighting scheme based on quality-data is applied in modeling process.•New hints about the past ...dynamical behavior of the South Atlantic Anomaly are shown.•Reversed flux patch linked to the South Atlantic Anomaly is detected since 950 AD.
The South Atlantic Anomaly (SAA) is one of the most outstanding features of the present geomagnetic field. Thus, a good knowledge of the SAA is clue for a better understanding of the dynamical behavior of the geomagnetic field. To achieve this goal, paleomagnetic data are crucial since they provide the unique way to investigate past changes in the Earth's magnetic field. Here, we present a new global geomagnetic field reconstruction, the SHAWQ2k model, which is based on a critical revision of the global archeomagnetic and volcanic dataset. The new model provides an improved description of the geomagnetic field during the last 2 millennia, and yields surprising outcomes about the emergence and development of the SAA. It shows that the reversed flux patch observed at the core-mantle boundary and linked to the SAA, emerged in the Southern Hemisphere from at least 950 AD. This patch moved westward from the equator to southern latitudes, being clearly isolated after 1400 AD. In addition, since 1550 AD a second reversed flux patch moving northeastward is observed in the North Atlantic. The new data now available for the Southern Hemisphere coming from Africa and South America together with the use of an appropriated weighting scheme in the modeling process have improved our understanding of past geomagnetic field behavior and showed new evolutionary aspects of the SAA.
In December 2019, the International Association of Geomagnetism and Aeronomy (IAGA) Division V Working Group (V-MOD) adopted the thirteenth generation of the International Geomagnetic Reference Field ...(IGRF). This IGRF updates the previous generation with a definitive main field model for epoch 2015.0, a main field model for epoch 2020.0, and a predictive linear secular variation for 2020.0 to 2025.0. This letter provides the equations defining the IGRF, the spherical harmonic coefficients for this thirteenth generation model, maps of magnetic declination, inclination and total field intensity for the epoch 2020.0, and maps of their predicted rate of change for the 2020.0 to 2025.0 time period.
•New archaeomagnetic data from the Early Iron Ages were obtained for Spain.•High geomagnetic fluctuation rates up to 8° and 16 μT/century were observed.•A new reconstruction model (SHAWQ-Iron Age) ...has been obtained.•New hints about the evolution of the Levantine Iron Age Anomaly (LIAA) are shown.•Normal flux patch (NFP) linked to the LIAA is observed at the core-mantle boundary.
Variations of geomagnetic field in the Iberian Peninsula prior to Late Iron Age times are poorly constrained. Here we report 14 directional and 10 palaeointensity results from an archaeomagnetic study carried out on 17 combustion structures recovered from six archaeological sites in eastern Spain. The studied materials have been dated by archaeological evidences and supported by radiocarbon dates (8th-5th centuries BC). Rock magnetic experiments indicate that the characteristic remanent magnetization is carried by a low coercivity magnetic phase with Curie temperatures of 500-575°C, most likely titanomagnetite/maghemite with low titanium content. Archaeointensity determinations were carried out by using the classical Thellier-Thellier experiment including pTRM-checks and magnetic anisotropy corrections. A new full vector Iberian Paleosecular Variation Curve for the Iron Age is presented. High fluctuation rates on both directions and intensities are observed during the Early Iron times that seems to be related with the Levantine Iron Age Anomaly (LIAA), the most prominent anomaly of the geomagnetic field of the last three millennia. Two intensity maxima were observed at Iberian coordinates, the oldest around 750 BC (associated with easterly declinations of around 23°) and the second 275 yrs later (475 BC) with northerly directions. The related virtual axial dipole moment was up to 14⋅1022 Am2 for the oldest materials (750 BC) and reaching 16⋅1022 Am2 for the materials corresponding to the end of the Early Iron Age.
In order to investigate the origin of the unusually high fluctuations of the palaeofield we have developed a new global geomagnetic field reconstruction, the SHAWQ-IronAge model, which is based on a critical revision of the global archeomagnetic and volcanic dataset. The new model provides an improved description of the evolution of the LIAA, which is related to a normal flux patch at the core-mantle boundary (CMB) below Arabian Peninsula clearly observed at around 950 BC. This flux patch expanded towards the north-west, while decreasing in intensity, reaching Iberia at around 750 BC. Around 600-500 BC, it underwent a revival below the European continent after that it seems to vanish in situ.
•State of the art of the lithosphere–atmosphere–ionosphere coupling (LAIC) mechanisms.•Earthquake-related case studies are shown together with unrelated cases.•Models of LAIC are proposed with future ...trends of research.
A systematic multi-parameter and multi-platform approach to study the slow process of earthquake preparation is fundamental to gain some insights on this complex phenomenon. In particular, an important contribution is the integrated analysis between ground geophysical data and satellite data. In this paper we review some of the more recent results and suggest the next directions of this kind of research. Our intention is not to detect a particular precursor but to understand the physics underlying the various observations and to establish a reliable physical model of the preparation phase before an impending earthquake. In this way, future investigation will search for suitable fore-patterns, which the physical model of multi-layers coupling predicts and characterizes by quasi-synchronism in time and geo-consistency in space. We also present alternative explanations for some anomalies which are not actually related to earthquakes, rather to other natural or anthropic processes.
•New 37 archeointensities for the Central Mediterranean (1500 BCE–150 CE).•First evidence of a rapid intensity change between 1070 and 1040 BCE in Greece.•The Levantine Iron Age Anomaly (LIAA) is ...present in the Central Mediterranean.•A global analysis suggests that the LIAA vanishes to the west and to the east.
The magnitude and origin of the Levantine Iron Age geomagnetic Anomaly (LIAA), which spanned the first half of the first millennium before the common era, are not yet well understood. Recent archeomagnetic studies from the Levant and Western Europe suggest a western drift of this feature, stressing the importance of investigating the temporal and spatial behaviour of this event over the Central Mediterranean area. To analyse this issue, we here present 37 new archeointensity data obtained from the archeomagnetic study of 118 ceramics and brick fragments collected in 8 archeological sites in Greece and Italy with ages ranging between 1500 BCE and 150 CE. The samples were analysed using the classical Thellier and Thellier method for paleointensity determination, including the correction for the anisotropy effect of the thermoremanent magnetization (TRM) and for the cooling rate dependence upon TRM acquisition. The results reveal the first evidence of a high-intensity peak in Greece between 1070 and 1040 BCE associated to high virtual axial dipole moment (VADM) values of around 140 ZAm2. A global analysis of available paleointensities suggests that the origin of these high values is the same to the one which produced the maximum VADM of the LIAA in the Levantine region. Our results suggest that the source of the LIAA is located in the Levantine region vanishing to the north, to the west and to the east where lower VADMs are observed. In addition, another high intensity maximum, less pronounced than the one of the LIAA, seems to be present around 500 BCE all over Europe, from the Canary Islands to Turkey showing similar VADM values (around 150 ZAm2) in the different regions. Both events seem to span over a large region at the Earth's surface covering more than 60° of longitude, verifying an Earth's outer core origin for these intensity features.
•New directional archaeomagnetic data from Cyprus.•The first directional secular variation curve for Eastern Mediterranean and Middle East.•Directional curvature changes during the last four ...millennia.•Insights on the directional occurrence of the Levantine anomaly.
We present new insights on the directional occurrence of the Levantine Iron Age Anomaly (LIAA) through the analysis of new and previously published directional archaeomagnetic data from Cyprus and nearby countries. The new directions, obtained from in situ baked clay structures such as small hearths and ovens from five Cypriot archaeological sites, dated from 2000 BCE to 1400 CE, are very well defined and are added to the scant reference dataset for Cyprus. The new records together with literature data from nearby countries are used to investigate the directional variations of the geomagnetic field in the Eastern Mediterranean and Middle East. The first directional palaeosecular variation curve for Middle East is calculated using a critical selection of reference data from Cyprus, Israel, Turkey and Syria. The curve covers the last four millennia and shows several periods characterized by abrupt directional changes. A maximum change in curvature is clearly observed around 900 BCE, characterized by a change rate as high as 13.2° per century. The new curve confirms that during the Levantine Iron Age Anomaly notable for extreme intensity values, the geomagnetic field was characterized by steep inclinations and important directional change too. The maximum curvature is shifted by around one century from the two distinct intensity spikes previously observed in Levant around the 10th and 8th centuries BCE. Other periods of important curvature change are also identified and deserve further investigation.
The main objective of this work is to compare directional (declination and inclination) volcanic and archaeomagnetic data for the last four centuries (~1600–1990) with the historical geomagnetic ...predictions given by the GUFM1 model which spans from 1590 to 1990. The results show statistical agreement between archaeomagnetic data and directions given by the geomagnetic field model. However, when comparing the volcanic data with the model predictions, marked inclination shallowing is observed. This systematically lower inclination has already been observed in local palaeomagnetic studies (Italy, Mexico and Hawaii) for the 20th century, by comparing recent lava flows with the International Reference Geomagnetic Field (IGRF) model. Here, we show how this inclination shallowing is statistically present at worldwide scale for the last 400 years with mean inclination deviation around 3° lower than the historical geomagnetic field model predictions.
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