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Recent studies indicate the existence of rapid fluctuations of the geomagnetic field intensity over the last 3000 years. These features have been observed during the first millennium BCE in the Mediterranean area (from Western and Central Europe to the Near East), and in other regions as the Canary and the Azores Islands, China and Korea. Nevertheless, due to the difficulty to obtain precise secular variation intensity curves, the spatial and temporal extension of these events, and the potential link between the different regional events observed are still under discussion. In this study, we focus on the rapid intensity decrease that seems to take place in central Asia during the second half of the 1st millennium BCE. We present 51 new archeointensity from South Uzbekistan, obtained by Thellier-Thellier method, also, rock magnetism experiments have been conducted in order to identify the principal magnetic minerals responsible for the magnetization. The results of those experiments show that the maghemite and/or magnetite, in some cases with low titanium content, are the main magnetic carriers. New data together with 73 previous archaeointensity data, allow us to better defined geomagnetic field intensity changes in South Uzbekistan between 600 BCE and 600 CE. The results indicate a rapid drop out in intensity between 500 BCE and 200 BCE with a minimum of 37.2 µT around 200 BCE ¿ 50 CE. A comparison with different VADMs values available for different regions indicates that similar intensity trends are observed during this period at the continental scale. Finally, the results are compared with Axial Dipole Moment estimations derived from different global models, suggesting that this sharp continental decrease is controlled by non-dipolar sources.

Reunión MAGIBER XI Portugal ,Condeixa a Nova (4 al 6 de septiembre de 2019), The geomagnetic field is a global feature with an important regional character. Its temporal and spatial variation can be observed from direct measurements such as satellites and logbook available since the 17th century. In order to know the behaviour of the geomagnetic field further in the past indirect measurements are needed. These indirect measurements (called paleo or archeomagnetic data) are based on the study of the remanent magnetization acquired by the iron oxides present in certain rocks and archaeological materials when heated at high temperatures (Néel, 1955)., This work was supported by two R&D&I projects, CERAC (HAR2016-75133-C3-1-P) led by V. Martínez and J.M. Gurt, and CONCERAC (HAR2016-75133-C3-3-P) led by E. Ariño, all funded by the Spanish Ministry of Science, Innovation and Universities. V. Martínez worked on this paper through the post-doctoral research contract Ramón y Cajal (RYC-2014-15789). M. Gómez-Paccard thanks to RYC-2013-14405. This congress was funded by Red de trabajo y laboratorios MAGIBERII (CGL2017-90632-REDT).

AGU Fall Meeting 2019 in San Francisco, 9 – 13 December 2019, Recent archeomagnetic studies provide new evidences for rapid variations of the intensity of the geomagnetic field in the last millennia. In particular, during the first millennium BC, one of the biggest jerks of the geomagnetic field took place. This phenomenon has been observed in the Near East, Israel and Georgia, Germany and Western Europe. The main purpose of this work is to study the behaviour of the geomagnetic field intensity in Central Asia during the first millennium BC, a region and period of time for which very few high- quality paleointensity data are available. For this purpose, an archaeomagnetic study has been conducted over a collection of 68 ceramic fragments coming from three archaeological sites in the south of Uzbekistan: Kampyr Tepe, where samples from three different sites have been studied: the Citadel (-262 ± 113 BC), the ceramic workshop (-150 ± 50 BC) and the Lower City (-129 ± 41 BC); Kurganzol (-325 ± 75 BC); and Termez, where samples came from different stratigraphic units with ages between 350 BC and 350 AD. The Kurganzol collection has been dated by a variety of archaeological and historical constraints, while the Kampyr Tepe and Termez ceramics were dated by 8 different radiocarbon analyses. During the first stage of this work, rock magnetism experiments have been conducted on 43 samples in order to identify the principal magnetic minerals responsible for the remanent magnetization. The results show that magnetite and/or Ti-magnetite are the main magnetic carriers. In a second stage, we have conducted paleointensity experiments following the Thellier classical methodology, including the TRM and cooling rate corrections necessary to ensure the reliability of paleointensity estimations. The new results, together with prior high-quality data, confirm that the geomagnetic field underwent a steep dropout in intensity between 600 BC and 100 BC in Central Asia. Finally, the VADM values have been compared with the dipolar moment variation predicted by several global geomagnetic models. This comparison indicates that the VADM values are higher than global model estimations, which might indicate the strong influence of non-dipolar sources upon the rapid decrease observed.

Trabajo presentado en el ESA Consultation for a Regional Initiative over the Mediterranean - MED, celebrado en Frascati (Italia), del 11 al 12 de diciembre de 2018, The Geosciences Institute (IGEO: http://www.igeo.ucm-csic.es/en/igeo) is a joint center of the Spanish Research Council (CSIC) -the largest public institution dedicated to research in Spain- and the Complutense University (UCM) –the largest university in Spain- carrying out cutting-edge research related to Geology, Geodesy and Geophysics using a multidisciplinary approach. The aim of this poster is to show the main research lines and needs of the IGEO directly linked to the priorities addressed in the MED 2018 consultation meeting. We shall present those of our current activities which are more suited to contribute to the Atmospheric science and applications theme -particularly in the coupled feedback atmosphere/ocean/continental surfaces section- but also have strong impact in both Ocean Science and Land Science (e.g. geoinformation systems, Climate impacts on land environment,…) themes. Some examples of IGEO’s capabilities include satellite observation (e.g., InSAR, optical, gravity and magnetic), combined with in situ data, land instability and deformation as well as structures and infrastructures instability, associated to geological and antropogenic hazards. We have also developed and implemented techniques for interpretation and modeling and the different level observation and results can be implemented and distributed using the European Plate Observing System (EPOS) ESFRI infrastructure. From the climate view point, additional our main priorities should be focused on: 1) Detection of weather regimes and synoptic systems with automatic methods to better understand the atmospheric circulation variability and change, 2) Weather and climate extreme events from different perspectives, including climate change attribution to human activities, and 3) Effect of weather regimes on air pollutants such as ozone and particulate matter to establish links between atmospheric composition and circulation. IGEO is included into CSIC's Natural Resources Research Area, which gathers nearly 20 research institutes, including various singular facilities (e.g. Doñana Biological Station (EBD: http://www.ebd.csic.es) or Mediterranean Institute of Advanced Research (IMEDEA: http://imedea.uib-csic.es/centre.php), and specialized centers (e.g. Ebro Observatory (OE: http://www.obsebre.es/). We shall also provide a brief overview of the activities, projects and initiatives carried out at CSIC where ESA's EO may definitively contribute.

Trabajo presentado en IAPSO-IAMAS-IAGA Assembly, celebrada en Cape Town (Sudáfrica), del 27 de agosto al 1 de septiembre de 2017, We present a new magnetic declination map for 1600-1640 AD based on the compilation carried out byAthanasius Kircher (1602-1680) in his book “Magnes sive de Arte Magnetica” ( ), published in 1641 and reedited in 1643 and 1654. In this The magnet or the magnetic art book Kircher presented a list of 524 observations of the magnetic declination made in different parts of the world, some of them were made by himself or by his supervision and other were compiled from navigators, other geomagnetic researchers or solicited by Kircher. He suggested in 1641 the possibility of drawing a magnetic map ( ) that Mapam Magneticam would present the values of declination on a world map, but he did not do so himself, this would have been the first magnetic map. We show here the magnetic map that he would have obtained. Only in one of the five tables shown in his book, Kircher provided information on the longitude of the measuring point, the list of measurements given by Ioanne Teliero on his trip to the East Indian. In the rest of the data only latitude and geographical information, often very uncertain, is provided on the location of the observation point. In this work we have relocated these observation points and corrected few mistakes. A total amount of 375 observations can be considered as reliable and were used to draw a coherent magnetic declination map. The new declination chart is compared with the expected values given by the GUFM1 model (Jackson et al. 2000) at the epoch 1638. The GUFM1 model is based in the compilation done by Jonkers et al. (2003) who used 3090 declination data for the time period between 1600 and 1640. Jonkers et al. (2003) did not used the 56 proper contributions of Kircher because not available information on the date measurement was provided in the Kircher's tables. However, after revision of the book, we are confident that those measurements were carried out in the 1600-1640 time period. It should be point out that few mistakes have been detected in the Kircher's compilation that were easily corrected.

Trabajo presentado en la X Reunión de la Comisión de Paleomagnetismo de la Sociedad Geológica de España, celebrada del 14 al 17 de septiembre de 2017 en el valle del río Grío, Zaragoza (España), En este trabajo se presenta una actualización de la base de datos direccional de Iberia para los últimos 3000 años (Gómez-Paccard et al., 2006) y el primer catálogo de intensidad para este periodo. En direcciones, la base de datos ha aumentado en más de un 80%, incluyendo más de 10 resultados direccionales no publicados hasta la fecha. En intensidades, este estudio representa un aumento de más del 50% en la cantidad de datos de calidad disponibles (si nos referimos al primer milenio a.C., se cuadruplica el número de datos), entendiendo datos de calidad como aquellos que cumplen los siguientes criterios: a) que el número de especímenes empleados para la determinación de la paleointensidad sea igual o superior a 4; b) que el protocolo empleado sea Thellier (Thellier y Thellier, 1959) o derivados; c) que la anisotropía de la imanación termorremanente haya sido investigada y corregida. Toda esta información ha permitido desarrollar nuevas curvas de variación paleosecular de declinación, inclinación e intensidad de Iberia para los tres últimos milenios. Se ha empleado el método bootstrap (Thébault y Gallet, 2010) incluyendo la jerarquía asociada a la información estratigráfica cuando estaba disponible. Las nuevas curvas direccionales no presentan grandes diferencias con las anteriormente publicadas (Fig. 1), aunque se incrementa su precisión. En intensidad las principales diferencias aparecen en el primer milenio a.C. y en el posible doble máximo en torno a 600-800 años d.C, que no es recogido por esta curva. Las nuevas curvas de variación paleosecular suponen una mejora en las posibilidades de la datación arqueomagnética en la península ibérica

Trabajo presentado en la X Reunión de la Comisión de Paleomagnetismo de la Sociedad Geológica de España, celebrada del 14 al 17 de septiembre de 2017 en el valle del río Grío, Zaragoza (España), En años recientes, las bases de datos de medidas arqueomagnéticas y volcánicas han crecido significativamente, aproximadamente un 40% en el caso de medidas direccionales y un 25% en medidas de intensidad. La mayor densidad de datos paleomagnéticos en Europa, en comparación con el resto del globo, permite desarrollar modelos regionales que cubran sólo esta zona, que se beneficien de una mayor resolución espacial y de la ausencia de influencia de outliers medidos fuera de la región. En este trabajo, se presenta un modelo regional de campo geomagnético actualizado que cubre los últimos tres milenios en Europa. El modelo ha sido obtenido utilizando la técnica R-SCHA-2D, que permite modelar el campo geomagnético sobre una porción en forma de casquete de la superficie de la tierra, aplicando métodos de regularización con significado físico. El campo magnético terrestre varía en el tiempo de forma continua, sujeta a observación directa sólo en la época reciente. Sin embargo, las medidas arqueo- y paleomagnéticas permiten conocer la naturaleza del campo geomagnético a lo largo de miles de años, aunque sólo en lugares e instantes puntuales. La modelización geomagnética permite generar reproducciones continuas del campo, mediante el ajuste de conjuntos de funciones matemáticas que representan el potencial magnético (Pavón-Carrasco et al. 2009, 2014, Constable et al., 2016). Uno de los usos más extendidos de los modelos de campo es la datación arqueomagnética, ya que permiten ubicar una medida en un tiempo dado según el grado de acuerdo con el modelo. Figura 1. Histogramas de las diferencias residuales entre el modelo y El conjunto de datos de partida está basado en la base de datos GEOMAGIA50.v3 (Brown et al., 2015), extendida utilizando la base de datos ArchaeoInt (Genevey et al., 2008). También se han utilizado datos de estudios recientes aún no incorporados a las bases de datos. La metodología de elaboración del modelo está basada en el método RSCHA-2D, descrito por Thebault 2008), que permite modelar campos vectoriales derivados de un potencial sobre un casquete esférico, y mejora el método clásico SCHA, descrito por Haines (1985). La modelización regional de datos DIF (declinación, inclinación, e intensidad, que resultan de medidas arqueo- y paleomagnéticas) conlleva varios problemas: el campo dipolar (que representa más del 90% del total) sólo puede ser representado regionalmente con armónicos de muy alto grado. Este obstáculo se puede sortear modelando sólo las diferencias locales entre el campo y un campo dipolar aproximado. Por otro lado, ya que los valores de declinación, inclinación e intensidad dependen de los coeficientes del modelo de forma no lineal, el problema debe ser linealizado antes de ser resuelto por inversión lineal. Finalmente, el problema inverso, en general, requiere añadir regularización para obtener soluciones con significado físico. Esto significa buscar una solución que minimice una norma elegida, que en nuestro caso es una combinación lineal de dB²r/dt² y B²r. Figura 2. Curvas de variación secular ubicadas en París para los últimos 3000 años, generadas con el modelo del presente estudio, comparadas con datos cercanos (a 900 km o menos de París, relocalizados vía polo), y con el modelo global SHA.DIF.14K. El modelo obtenido presenta un buen compromiso entre la suavidad temporal y espacial y el error rms respecto a los datos. Además, se ha estimado su error estadístico mediante una técnica bootstrap. Esto facilita su uso como herramienta de datación, permitiendo obtener no sólo una fecha estimada, sino también intervalos temporales de confianza para la datación.

Trabajo presentado en la International Conference on Rock Magnetism, celebrada en Utrech (Países Bajos) del 10 al 14 de julio de 2017, We present the first update of the archaeomagnetic data catalogue for the Iberian Peninsula covering the last 3000 years. The first archaeomagnetic data compilation for Iberia was published in 2006, including 63 archaeomagnetic directions and making possible the generation of the first directional Palaeosecular Variation Curve (PSVC) in Iberia. Since then, the number of directional data has increased by more than 80%, of which around 20% have been studied in this work. Regarding archaeointensity data, we present 20 new high quality archaeointensities, in addition to previously published ones (about 100 data), by creating the first archaeointensity catalogue for Iberia spanning the last 3000 years. The different qualities of the data included in this Iberian dataset have been evaluated following different palaeomagnetic criteria, such as the number of specimens analysed, the laboratory protocol applied and the kind of material studied. The improvement of the database is especially notable for the first millennium BC (about 50% of the new included data), a period for which there was not possible to develop an intensity palaeosecular variation curve due to the lack of high quality archaeointensity data. This new compilation of archaeomagnetic data has provided enough new information to generate the first PSVC of the geomagnetic full vector for Iberia for the last three millennia, which have been obtained by hierarchical bootstrap method using only selected high quality data from the catalogue in order to obtain the most reliable secular variation curve. No important differences between these curves and those calculated from regional and global geomagnetic field models are registered, with the most notable discrepancies observed in the intensity curve and during the first millennium BC. These new PSVCs offer a comprehensive view of the variations of the geomagnetic field in Iberian Peninsula and is suitable as a Master Curve in the archaeomagnetic dating technique for archaeological combustion structures located in this region.

Trabajo presentado en la European Geosciences Union General Assembly, celebrada en Viena (Austria), del 23 al 28 de abril de 2017, In 2006, the first Iberian archaeomagnetic catalogue for the last 3000 years was presented, including 63 archaeomagnetic directions coming from Spanish archaeological sites. Since then, several archaeomagnetic studies have been carried out in order to cover the main temporal gaps present in this catalogue: the first millennium BC and the Late Roman – High Middle Ages. In this work, the first update of this catalogue is proposed. The directional database has increased by more than 80% (around 50 new data), of which more than 10 palaeodirections come from new studies that had not been previously published. The improvement of the database is especially notable in the first millennium BC, representing more than 50% of the available data in the first directional catalogue for Iberia (around 30 directions). This updated database has provided enough new information to generate a revised directional Palaeosecular Variation Curve (PSVC) for Iberia spanning the last three millennia using the bootstrap technique. This new PSVC offers a comprehensive view of the evolution of the geomagnetic field in this region and is suitable as a Master Curve in the archaeomagnetic dating technique for archaeological combustion structures located in the Iberian Peninsula.

Trabajo presentado en la European Geosciences Union General Assembly, celebrada en Viena (Austria), del 23 al 28 de abril de 2017, In 2006, the first Iberian archaeomagnetic catalogue for the last 3000 years was presented, including 63 archaeomagnetic directions coming from Spanish archaeological sites. Since then, several archaeomagnetic studies have been carried out in order to cover the main temporal gaps present in this catalogue: the first millennium BC and the Late Roman – High Middle Ages. In this work, the first update of this catalogue is proposed. The directional database has increased by more than 80% (around 50 new data), of which more than 10 palaeodirections come from new studies that had not been previously published. The improvement of the database is especially notable in the first millennium BC, representing more than 50% of the available data in the first directional catalogue for Iberia (around 30 directions). This updated database has provided enough new information to generate a revised directional Palaeosecular Variation Curve (PSVC) for Iberia spanning the last three millennia using the bootstrap technique. This new PSVC offers a comprehensive view of the evolution of the geomagnetic field in this region and is suitable as a Master Curve in the archaeomagnetic dating technique for archaeological combustion structures located in the Iberian Peninsula.

Trabajo presentado en la X Reunión de la Comisión de Paleomagnetismo de la Sociedad Geológica de España, celebrada del 14 al 17 de septiembre de 2017 en el valle del río Grío, Zaragoza (España), The rate of production of cosmogenic isotopes, such as 14C or 10Be, plays an important role in our understanding of the solar-terrestrial relationship since radionuclides records stored in polar ice cores and tree rings offer the unique way to reconstruct changes in the solar total irradiance during the Holocene (see Usoskin, 2017, for a review). To accurately determine past solar activity, the effect of the variability of the geomagnetic field upon the production of cosmogenic radionuclides needs to be properly considered since the Earth´s magnetic field greatly modulates the rate of isotope production in the atmosphere. Up to now, it has been assumed that the long-term time variation of isotope production rate is mainly modulated by changes in the geomagnetic field whereas the solar magnetic field dominates shorter time wavelengths (Snowball and Muscheler, 2007; Usoskin et al., 2016). Here we reanalyse this assumption by demonstrating that the geomagnetic field also exerts a strong modulation of high-frequency (periods of ∼800 yr) atmospheric radiocarbon production rates that are currently being wrongly associated to solar activity. Specifically, we identify for the first time a clear and robust coherence, in terms of amplitude and phases, between the production rate curve directly derived from the geomagnetic field reconstruction derived from the SHA.DIF.14k global model (PavónCarrasco et al., 2014) and the original isotope production curve for the Holocene (Steinhilber et al., 2012). Our results provide a new vision of the mechanisms causing the observed isotope production variability and, hence, are crucial to re-evaluate past solar forcing and use it as a benchmark to test links between climate and total solar irradiance in the next generation of climate models.

Trabajo presentado en el Symposium "El Castillón: un centro de poder a orillas del esla. De la prehistoria reciente a la edad media", celebrado en Salamanca (España), los días 8 y 9 de Junio de 2017

Trabajo presentado en IAPSO-IAMAS-IAGA Assembly, celebrada en Cape Town (Sudáfrica), del 27 de agosto al 1 de septiembre de 2017, The production rates of cosmogenic isotopes, such as 14C and 10Be, are directly modulated by the strength of the Solar and Earth magnetic fields. Changes in the isotope production rate during the Holocene are estimated mainly from isotopic sampling in tree and ice cores, while the past evolution of the geomagnetic field can be recovered from well‐dated rock samples containing magnetic minerals than can be used to obtain the so‐called paleomagnetic data. However, no indirect measurements provide the past solar activity. Estimates of solar forcing play an important role in understanding paleoclimatic temperature reconstructions and as boundary conditions in simulations with climate models due to its influence to modify the energy balance of the Earth. Nowadays, different studies consider that both magnetic fields affect the production rate at two different timescales: the long‐term modulation is associated to changes in the geomagnetic field and the shorter variations to the past solar activity. However, the most recent palaeomagnetic reconstructions developed during the last years provide a new picture with higher temporal resolution of the past variations of the strength of the Earth’s magnetic field. In this work, we revisit the connection between the past evolution of the Earth’s magnetic field and the production rates of 14C and 10Be for the Holocene by means of the more complete paleomagnetic database and the most recent geomagnetic reconstructions.

Trabajo presentado en el IX Congreso Geológico de España, celebrado en Huelva (España), del 12 al 14 de septiembre de 2016, El objetivo de este trabajo es mejorar la curva patrón de variación paleosecular (PSVC) de la Península Ibérica, aportando un dato más en una época en la que apenas hay datos arqueomagnéticos en Iberia: el periodo Tardorromano-Alta Edad Media. Para ello se han estudiado las propiedades magnéticas y la estructura de la remanencia magnética de dos hornos del yacimiento del Cerro de los Almadenes, localizado en Otero de Herreros (Segovia). Se ha realizado la desimanación sistemática por campos alternos decrecientes de 16 especímenes, aislando adecuadamente la dirección característica y obteniendo una dirección media de buena precisión. Los resultados obtenidos se incorporarán al catálogo de datos arqueomagnéticos de Iberia. Por otra parte, se ha comparado la datación por termoluminiscencia realizada previamente, siendo de 498 d.C ± 95 años, con la datación arqueomagnética obtenida en este estudio: 431d.C - 517d.C., comprobando la validez de la técnica así como de la aproximación regional y el uso del modelo SCHA.DIF.3k.

Trabajo presentado en el IX Congreso Geológico de España, celebrado en Huelva (España), del 12 al 14 de septiembre de 2016, En este trabajo se presenta un simple modelo browniano que es capaz de reproducir las características generales de la evolución del momento dipolar axial del campo magnético terrestre en escalas de millones de años. El modelo está basado en el movimiento de una partícula afectada por la combinación de un potencial con dos pozos simétricos y un ruido ¿térmico¿ gaussiano, de forma que el momento dipolar axial oscila en torno a las posiciones estables del potencial y eventualmente es capaz de cambiar de signo simulando una inversión. Se analizan los resultados del modelo comparándolos con la secuencia de polaridades real y se discuten sus principales diferencias y semejanzas. Asimismo se estudia el efecto que tienen las variaciones de los parámetros del modelo en los resultados del mismo

Trabajo presentado en el IX Congreso Geológico de España, celebrado en Huelva (España), del 12 al 14 de septiembre de 2016, En este trabajo se presentan los resultados de la datación arqueomagnética llevada a cabo en tres hornos medievales en el yacimiento de la Avenida de las Ollerías, en Córdoba. Un total de 40 especímenes fueron desimanados en el laboratorio de paleomagnetismo de la UCM con técnicas de desmagnetización térmica y por campos alternos decrecientes (AF). Para la datación arqueomagnética se ha utilizado la herramienta de software archaeo_dating, y la curva sintética de Variación Paleosecular generada por el modelo regional (SCHA.DIF.3K). Dos de los hornos investigados presentan direcciones estadísticamente indistinguibles y una edad común para su último uso en torno a 1200 d. C. El tercer horno aporta una cronología más antigua, su último uso se sitúa en el periodo 838 ¿ 1025 d.C. Los resultados son consistentes con las observaciones arqueológicas que los sitúan entre los siglos X y XIII d.C., siendo uno de ellos algo más antiguo que el resto.

Trabajo presentado en el 9ª Asamblea Hispano Portuguesa de Geodesia y Geofísica, celebrada en Madrid (España), del 28 al 30 de junio de 2016, [ES] El campo geomagnético generado por el núcleo externo de la Tierra tiene una dependencia temporal: la llamada variación secular. Ésta se caracteriza por ser de largo período temporal, pero a veces sufre bruscas fluctuaciones de distinta naturaleza y origen. Cuando estas sacudidas ocurren a escala mensual son denominadas jerks geomagnéticos. Por el contrario, los cambios bruscos en la variación secular de largo período (decenas de años) son referidos como jerks arqueomagnéticos. Ambos fenómenos tienen origen en el núcleo externo de la Tierra donde el campo es generado: los primeros son la consecuencia de oscilaciones que rompen la simetría axial y ecuatorial del campo geomagnético, mientras que los de más largo período podrían estar relacionados con variaciones del campo toroidal. Sin embargo, no existe aún un consenso general acerca de los orígenes de los jerks. En este trabajo se presenta un análisis de los jerks y sus principales características, a través de modelos geomagnéticos de campo principal, basados tanto en datos instrumentales recientes (CHAOS-5 que cubre los últimos 20 años) como en datos paleomagnéticos (SHA.DIF.14k, que abarca los últimos 14 milenos)., [EN] The geomagnetic field generated by Earth’s outer core shows a dependence with time, known as secular variation. This variation is characterized by its long temporal period, except for occasional sudden fluctuations, diverse in nature and origin. When these shifts occur over times on the scale of months, they are known as geomagnetic jerks. On the other hand, abrupt changes in long period secular variation (on the order of decades), are referred to as archaeomagnetic jerks. Both phenomena have their source in Earth’s outer core, where the geomagnetic field is generated: the first are a consequence of axial and equatorial symmetry-breaking oscillations of the geomagnetic field, while longer-period jerks might be related to toroidal field variations. However, there is as of yet no general consensus about the origins of jerks. In this work, a general analysis of jerks and their properties is presented, via core field models based on recent data (CHAOS-5, covering the last 20 years) as well as palaeomagnetic data (SHA.DIF.14k, covering the last 14 millenia).

Trabajo presentado en el 9ª Asamblea Hispano Portuguesa de Geodesia y Geofísica, celebrada en Madrid (España), del 28 al 30 de junio de 2016, [ES] Se presenta un modelo muy simple de campo magnético terrestre basado en una partícula browniana con inercia afectada por un ruido térmico gaussiano y sometida a un potencial con dos pozos simétricos. La posición de la partícula representa el momento dipolar axial del campo magnético terrestre de forma que éste presenta oscilaciones estocásticas en torno a los mínimos de potencial y siendo posible que la partícula salte de un pozo a otro, lo que representa una inversión del campo. Se analizan los resultados del modelo y se comparan sus características con el comportamiento del campo magnético en escalas de millones de años., [EN] We present a simple model of Earth magnetic field based on a Brownian particle with inertia affected by a Gaussian thermal noise and under the action of a symmetric double-well potential. The position of the particle represents the axial dipole moment of geomagnetic field so that it shows stochastic oscillations around potential minima, being possible that the particle jumps from one well to the other, which represents a geomagnetic reversal. We analyse model results and compare its characteristics with the geomagnetic field behaviour in scales about millions of years.

Trabajo presentado en la EGU General Assembly 2016 (European Geosciences Union), celebrada en Viena (Austria) del 17 al 22 de abril de 2016., Over the last years new evidences of several short-lived regional maxima of the geomagnetic field intensity at various times and locations have been defined. These features have important implications both for geomagnetic field modeling and for Earth0 s dynamo simulations. However, the nature, extent and underlying causes of these variations are still poorly understood. Here we present a detailed analysis of the sharp abrupt intensity change that took place in Western Europe around 800 AD, the most significant geomagnetic field intensity feature observed in Europe over the last two millennia. For this purpose we present an up-to-date regional intensity reconstruction for Western Europe and compare the results with other regional and global geomagnetic field reconstructions. The results indicate that the 800 AD event is mainly controlled by non-dipolar geomagnetic sources.

Trabajo presentado en la EGU General Assembly 2016 (European Geosciences Union), celebrada en Viena del 17 al 22 de abril de 2016., Variation of geomagnetic field changes in the Iberian Peninsula between prior to roman times remain very poorly constrained. Here we report results from the archeomagnetic study carried out on four set of ceramics and one combustion structure recovered in two pre-roman (celtiberic) archeological sites in central Spain. Rock magnetic experiments indicate the ChRM is carried by magnetite. Archaeointensity determinations were carried out by using the classical Thellier-Thellier experiment including tests and corrections for magnetic anisotropy and magnetic cooling rate dependency. Well heated specimens (red ceramic fragments and well heated samples from the kiln) show one single well defined component of magnetisation going through the origin and a linear arai plot providing successful archaeointensity determinations. The effect of anisotropy of the termoremanent magnetization (ATRM) on paleointensity analysis was specially investigated obtaining very high ATRM corrections on fine pottery specimens. With differences between the uncorrected and ATRM corrected paleointensity values that reached up to 80-100%. Mean intensity values obtained from three selected groups were 61.1 5.9 T; 57.6 3.3 and 56.4 4.7 T which allows delineate the evolution of the paleofield intensity in central Iberia during the III-I centuries BC. The new archaeointensity data disagrees with previous results from Iberian ceramics which were not corrected by the ATRM effect. But they are in agreement with the most recent French paleointensity curve and latest European intensity model. Both based on a selection of high quality paleointensity data. This result reinforces the idea that the puzzling scatter often observed in the global paleointensity database is likely due to differences in the laboratory protocol. Further data from well contrasted laboratory protocols are still necessary to delineate confidently the evolution of the geomagnetic paleofield during the first millennium BC.