The available European database of archeomagnetic field values and instrumental data has been used to produce a regional model for the geomagnetic field in Europe for the last 3000 years (from 1000 B.C. to 1900 A.D., connecting with the epoch covered by the IGRF models). This new model, SCHA.DIF.3K, constitutes an improvement with respect to the previous regional archeomagnetic model SCHA.DI.00‐F, which used relocated values and was only valid for the last 2000 years. The new model has been obtained by least sums of absolute deviation inversion of paleomagnetic data using spherical cap harmonics for the spatial representation of the field and sliding windows in time. An algorithm has been developed to jointly model the three archeomagnetic elements declination, inclination, and intensity. The resulting model provides the direction and intensity of the Earth's magnetic field over the European continent, northern Africa, and western Asia for the last 3000 years. The fit to the European archeomagnetic database is more accurate than that provided by global archeomagnetic models. In addition, this model represents a step forward in archeomagnetic dating studies (since the relocation error is avoided) and can also be used to study the rapid changes of the geomagnetic field (archeomagnetic jerks) that have been recently proposed.

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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. Confidential manuscript submitted to Earth and Planetary Science Letters • earthquake [e.g. Occhipinti et al., 2013, and references therein]. This offers the possibility to retrieve seismic information from ionospheric observations. An important and debated question arises about the possibility that, during the phase of EQ preparation, electromagnetic waves and/or particles could be transferred from the solid Earth (in particular the lithosphere) to the atmosphere, with a particular effect in the ionosphere, above around 50 km [e.g. Pulinets and Boyarchuk, 2004; Freund, 2011; Pulinets and Ouzounov, 2011; De Santis et al., 2015]. One of the most general models of coupling is based on the emission of a radioactive gas [Pulinets and Boyarchuk, 2004] or metallic ions [Freund, 2011] before a large earthquake, which may change the distribution of electric potential above the surface of the Earth and then up to the ionosphere [e.g., Pulinets and Boyarchuk, 2004; Sorokin et al., 2001]. Penetration of the electric field to the ionosphere could produce ionospheric plasma density and/or conductivity anomalies, which are observed above seismic zones [e.g., Liu et al., 2006; Kon et al., 2011]. An alternative explanation is that the radon emitted before an earthquake would increase the conductivity of air at ground level and that the ensuing increase of current in the fair weather global circuit would lower the ionosphere [Harrison et al. 2010]. Therefore, it is expected that low Earth orbiting (LEO) satellites could be the best possible dedicated platforms of sensors to detect any electromagnetic, acoustic or infrared seismic-linked precursors. Certainly, space observations have to be investigated together with ground (and near-surface) seismic and other geophysical observations, in order to have a more complete picture of the possible involved phenomena.

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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.

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The SCHA.DI.00 directional model for the geomagnetic field in Europe for the last 2000 years (PAVóN-CARRASCO et al., 2008) has been updated by modelling the palaeointensity. This model, SCHA.DI.00, was developed from available Bayesian European Palaeosecular Variation Curves using the regional Spherical Cap Harmonic Analysis technique. The comparison of the palaeosecular variation curves, given by the regional model, with available archaeomagnetic data not used in its development showed an improvement with respect to the fit obtained by global archaeomagnetic models. In this paper advantage is taken of recently published palaeointensity databases to develop a complete (direction and intensity) regional archaeomagnetic model for the last 2000 years valid for the European region: the SCHA.DI.00-F model. Not only does this complete model provide an improvement for example for archaeomagnetic data studies, but it is also shown that this new regional model can be used to study the recently proposed link between the centennial secular variation of the geomagnetic field and climate change. The pattern of the archaeosecular variation of the field intensity obtained by SCHA.DI.00-F seems to verify the hypothesis presented by GALLET et al. (2005) about a possible (causal) connection between changes in the geomagnetic field intensity and in climate parameters, opening the door for more discussions on this challenging subject.