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Unraveling the short‐term behavior of the Earth's past geomagnetic field at regional scales is crucial for understanding its global behavior and, thus, the dynamics of the deep Earth. In this context, obtaining accurate full‐vector geomagnetic field records from regions where archeomagnetic data are absent becomes essential. Here, we present the first full‐vector archeomagnetic data from Central Asia, derived from the analysis of nine archeological kilns sampled in South Uzbekistan, dating back to the period between 200 BCE and 1429 CE. To obtain these new data, we conducted thermal and alternating field demagnetization procedures, along with Thellier‐Thellier paleointensity experiments, including partial thermoremanent magnetization checks, thermoremanent magnetization anisotropy and cooling rate corrections. The comparison between the new data, previous selected data from Central Asia, and available global models reveals important differences between approximately 400 BCE and 400 CE, especially concerning the geomagnetic field intensity element. In order to investigate this in detail, we have developed a regional update of the SHAWQ global models family by incorporating, for the first time, high‐quality data from Central Asia. The results suggest that this deviation is linked to non‐dipolar sources of the geomagnetic field in Central Asia reaching a maximum contribution around the first century BCE. According to the updated global paleoreconstruction, this non‐dipole feature, manifested at the Earth's surface as low intensities, is associated with the presence of a reversed flux patch at the core‐mantle boundary beneath this region. Plain Language Summary: The geomagnetic field is a global feature that changes over time and space. These changes are known over the last few centuries through direct observations collected by satellites and geomagnetic observatories. However, indirect measurements, based on the paleomagnetic study of archeological and geological materials, are needed to disentangle geomagnetic field behavior over longer time scales. In this context, archeomagnetism is the discipline that studies the direction and strength of the past geomagnetic field by investigating the magnetic properties of well dated archeological baked clay material. In order to properly describe the behavior of the Earth's magnetic field it is crucial to have a good temporal and spatial coverage of archeomagnetic data. In this work, we present the first full‐vector archeomagnetic data for Central Asia, a large region that remained unexplored from an archeomagnetic point of view. The new data were obtained from 9 kilns excavated in South Uzbekistan, with ages ranging from 200 BCE to 1429 CE. We then developed a regional update of the SHAWQ global models family by incorporating, for the first time, high‐quality archeomagnetic data from Central Asia. The results indicate a relevant non‐dipole feature presented over this region around the first century BCE. Key Points: First nine full‐vector archeomagnetic data for Central Asia for the last 2k yearsResults indicate a large non‐dipole contribution around the first century BCE in Central AsiaCentral Asia intensity data reveal a reversed flux patch at the core‐mantle boundary [ABSTRACT FROM AUTHOR]

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Recent paleomagnetic studies have shown that important short‐lived intensity fluctuations occurred during the first millennium BCE. However, the knowledge of the spatial and temporal extension of these features is still limited by the scarce availability of robust data. In this study we focus on the study of the intensity decrease that took place in Central Asia during the second half of the 1st millennium BCE after the high intensities that characterized the Levantine Iron Age Anomaly. Since previous archeointensities available for this period and region were obtained without accomplishing modern standards of quality, we present here new archeointensities that are derived from classical Thellier and Thellier experiments, including partial thermoremanent magnetization (pTRM) checks, thermoremanent magnetization (TRM) anisotropy and cooling rate corrections at the specimen level. The new 51 archeointensities, together with previous archeointensities, have been used to present a new local paleosecular variation curve for Central Asia. The results confirm the existence of an important geomagnetic field intensity decrease in South Uzbekistan from the 4th century BCE to the end of the 1st century BCE associated with rates of changes up to −15 μT/century. A critical analysis of the archeointensity global database indicates that this feature was present at continental scale, from Western Europe to Central Asia. However, this trend is not identified in other regions such as Japan or Mexico. Finally, the comparison with the dipole moment derived from recent global geomagnetic field reconstructions suggests a strong influence of non‐dipolar sources upon this continental intensity feature. Plain Language Summary: The Earth's magnetic field (also called the geomagnetic field) is continuously changing over time and space. Since the 19th century, the behavior of the geomagnetic field is known through direct observations performed in geomagnetic observatories and satellites. However, the only way to recover past geomagnetic field in ancient times is through paleomagnetic and archeomagnetic studies. In particular, archeomagnetism is the study of heated archeological materials, which include ferromagnetic particles acting as a compass and recording the geomagnetic field direction and strength at a certain time. When the archeological material cools down the ferromagnetic particles save the direction and intensity, like a photograph of the ancient geomagnetic field. Nowadays, there are very few archeomagnetic studies dealing with archeological materials from Central Asia. In this work, we present the variation of the geomagnetic field intensity between 600 BCE–600 CE in Uzbekistan deduced from a complete archeomagnetic investigation of 70 pottery fragments. The results confirm a rapid variation of geomagnetic field strength between 400 BCE and 100 BCE–1CE. To determine the spatial expression of this feature, we compared the obtained trend for Central Asia with the geomagnetic field intensity evolution in other regions of the world. Key Points: We present 51 new thermoremanent magnetization‐anisotropy corrected archeointensities for South UzbekistanAn important decrease in intensity is observed between 400 BCE and 100 BCE–1 CE, probably associated with non‐dipolar sourcesSimilar intensity V‐shaped trends are observed at continental scale [ABSTRACT FROM AUTHOR]

The equivalent source method of Spherical Elementary Current Systems (SECS) has contributed valuable results for spatial magnetic interpolation purposes where no observations are available, as well as for modeling equivalent currents both in the ionosphere and in the subsurface, thus providing a separation between external and internal sources. It has been successfully applied to numerous Space Weather (SW) events, whereas some advantages have been reported over other techniques such as Fourier or Spherical (Cap) Harmonic Analysis. Although different modalities of SECS exist (either 1‐D, 2‐D, or 3‐D) depending on the number of space dimensions involved, the method provides a sequence of instantaneous pictures of the source current. We present an extension of SECS consisting in the introduction of a temporal dependence in the formulation based on a cubic B‐splines expansion. The technique thus adds one dimension, becoming 4‐D in general (e.g., 3‐D + t), and its application is envisaged for, though not restricted to, the analysis of past events including heterogeneous geomagnetic data sets, such as those containing gaps, different sampling rates or diverse data sources. A synthetic model based on the SW Modeling Framework is used to show the efficacy of the extended scheme. We apply this method to characterize the current systems of past and significant SW events producing geomagnetically induced currents, which we exemplify with an outstanding geomagnetic sudden commencement occurred on 24 March 1991. Plain Language Summary: Spherical Elementary Current Systems is a mathematical technique that allocates an electrical current system as the source of the geomagnetic perturbations typically recorded by ground magnetometers. Such a current system is assumed to flow on a sheet at a certain height/depth from the surface. Traditionally, Spherical Elementary Current Systems is a purely spatial technique, which is appropriate if we rely on homogeneous time series at each observation site. Otherwise, the information is typically concentrated at certain timestamps and sparse at others, resulting in uneven source currents being modeled. We have extended the traditional technique by including a time expansion, thus allowing spatial information to be shared across time. This produces a smoother, more realistic equivalent source current, as shown by comparing both techniques with the results of a synthetic model. We have also applied the extended method to an outstanding geomagnetic sudden commencement occurred on 24 March 1991. Key Points: The technique of Spherical Elementary Current Systems has been extended by including a temporal dependence based on cubic B‐splinesImprovement is achieved when dealing with heterogeneous data sets consisting of geomagnetic ground data sampled at diverse ratesThe method can be used to characterize the equivalent current systems of past and significant Space Weather events [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

In this work, we present 16 directional and 27 intensity high‐quality values from Iberia. Moreover, we have updated the Iberian archeomagnetic catalogue published more than 10 years ago with a considerable increase in the database. This has led to a notable improvement of both temporal and spatial data distribution. A full vector paleosecular variation curve from 1000 BC to 1900 AD has been developed using high‐quality data within a radius of 900 km from Madrid. A hierarchical bootstrap method has been followed for the computation of the curves. The most remarkable feature of the new curves is a notable intensity maximum of about 80 μT around 600 BC, which has not been previously reported for the Iberian Peninsula. We have also analyzed the evolution of the paleofield in Europe for the last three thousand years and conclude that the high maximum intensity values observed around 600 BC in the Iberian Peninsula could respond to the same feature as the Levantine Iron Age Anomaly, after travelling westward through Europe. Plain language summary: Knowledge of the Earth's magnetic field plays an important role on the understanding of its dynamics. By measuring certain rocks or archeological objects from around the world, we can determine the field's shape and intensity in former times. Knowing its evolution is essential to understand how this field is generated, how it has varied through time and how it may behave in the future. In this work, we present new measurements of the magnetic field from the Iberian Peninsula that provide useful constraints on the magnetic field for archeological times that currently lack information. We have updated the compilation of Iberian data for the last 3,000 years and calculated a new reference curve for the magnetic field for this region. We have found that the magnetic field was particularly intense in the Iberian Peninsula about 2,600 years ago. By comparing this result with data from Europe and the Middle East, we observe that this high intensity has been moving from east to west through southern Europe. This feature is probably related with the rapid intensity change (the geomagnetic spike) recently discovered in the Levantine region. Key Points: We have obtained 16 archeomagnetic directions and 27 high‐quality archeointensity dataA new full vector paleosecular variation curve for the last three millennia in Iberia is presentedThe new curve shows a high‐intensity maximum around 600 BC that might be related to the Levantine Iron Age Anomaly moving through Europe [ABSTRACT FROM AUTHOR]