Dipole moment of the geomagnetic field (last 3000 years) : applications to the paleoclimatology

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física de la Tierra, Astronomía y Astrofísica I (Geofísica y Meteorología), leída el 24-02-2017Para dar respuesta a las preguntas más relevantes dentro del campo de las Ciencias de la Tierra, como cuál es el origen del campo magnético terrestre, si estamos actualmente en un proceso de inversión del campo geomagnético y qué consecuencias podría tener sobre la vida humana, o si existe una relación entre el campo geomagnético y el clima, primero hay que preguntarse si nuestro conocimiento actual de la evolución pasada del campo magnético terrestre es lo suficientemente realista como para sacar conclusiones robustas, al menos para los últimos tres milenios. La evolución del campo geomagnético en el pasado se conoce gracias a las reconstrucciones globales, regional y locales que se realizan a partir de los datos instrumentales (de satélites y observatorios), históricos y, para épocas más antiguas, paleomagnéticos. Lamentablemente, la base de datos paleomagnéticos está muy pobremente distribuida espacio-temporalmente, incluso en el periodo con más datos disponibles, los últimos 3000 años. Su efecto en la seguridad con la que conocemos el campo geomagnético en el pasado y su cuantificación serían de vital importancia para dar respuesta a las preguntas con la que comenzamos esta sección. Además, la evolución del campo geomagnético en el pasado no es únicamente utilizada en el marco del Geomagnetismo, sino que existen múltiples aplicaciones a otras disciplinas. En esta tesis nos centraremos en dos de sus aplicaciones al campo de la Paleoclimatología: si existe una relación entre el campo geomagnético y el clima; y las correcciones por el campo geomagnético realizadas sobre los ritmos de producción de isótopos cosmogénicos en la atmósfera terrestre para determinar las reconstrucciones de actividad solar de los últimos 2000 años, usadas en modelos de variabilidad climática para reconstruir el clima del pasado...In order to answer the most relevant questions in the field of Earth Sciences, i.e. what is the origin of the Earth's magnetic field, if a process of reversal of the geomagnetic field is currently occurring and what consequences might have on human life, or if there is a relation between the geomagnetic field and past climate, first we must know if our current knowledge of the past evolution of the Earth's magnetic field is realistic enough to draw robust conclusions, at least for the last three millennia. The evolution of the geomagnetic field in the past is known thanks to the global, regional and local reconstructions from the instrumental data (from satellites and observatories), historical and, for older times, palaeomagnetic data. Unfortunately, the palaeomagnetic database is very poorly distributed in space and time, even for the period with the most data available: the last 3000 years. Its effect on the accuracy of our knowledge on the geomagnetic field in the past and its quantification would be of vital importance to answer the question with which we start this section. In addition, the past evolution of the geomagnetic field is not only used in the framework of Geomagnetism, but also in other disciplines. In this thesis we will focus on two of its applications in the field of Palaeoclimatology: if there is a connection between the geomagnetic field and the climate in the past; and the corrections by the geomagnetic field carried out on the rates of production of cosmogenic radionuclides in the atmosphere used to determine the reconstructions of solar activity of the last 2000 years, and in climate variability models to reconstruct the climate of the past...Depto. de Física de la Tierra y AstrofísicaFac. de Ciencias FísicasTRUEunpu

New perspectives in the study of the Earth's magnetic field and climate connection: the use of transfer entropy

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

Multi-centennial fluctuations of radionuclide production rates are modulated by the Earth's magnetic field

The production of cosmogenic isotopes offers a unique way to reconstruct solar activity during the Holocene. It is influenced by both the solar and Earth magnetic fields and thus their combined effect needs to be disentangled to infer past solar irradiance. Nowadays, it is assumed that the long-term variations of cosmogenic production are modulated by the geomagnetic field and that the solar field dominates over shorter wavelengths. In this process, the effects of the non-dipolar terms of the geomagnetic field are considered negligible. Here we analyse these assumptions and demonstrate that, for a constant solar modulation potential, the geomagnetic field exerts a strong modulation of multi-centennial to millennial wavelengths (periods of 800 and 2200 yr). Moreover, we demonstrate that the non-dipole terms derived from the harmonic degree 3 and above produce maximum differences of 7% in the global average radiocarbon production rate. The results are supported by the identification, for the first time, of a robust coherence between the production rates independently estimated from geomagnetic reconstructions and that inferred from natural archives. This implies the need to review past solar forcing reconstructions, with important implications both for the assessment of solar-climate relationships as well as for the present and future generation of paleoclimate models

Eccentric Dipole Evolution during the Last Reversal, Last Excursions, and Holocene Anomalies. Interpretation Using a 360-Dipole Ring Model

The eccentric dipole (ED) is the next approach of the geomagnetic field after the generally used geocentric dipole. Here, we analyzed the evolution of the ED during extreme events, such as the Matuyama-Brunhes polarity transition (~780 ka), the Laschamp (~41 ka) and Mono Lake (~34 ka) excursions, and during the time of two anomalous features of the geomagnetic field observed during the Holocene: the Levantine Iron Age Anomaly (LIAA, ~1000 BC) and the South Atlantic Anomaly (SAA, analyzed from ~700 AD to present day). The analysis was carried out using the paleoreconstructions that cover the time of the mentioned events (IMMAB4, IMOLEe, LSMOD.2, SHAWQ-Iron Age, and SHAWQ2k). We found that the ED moves around the meridian plane of 0–180◦ during the reversal and the excursions; it moves towards the region of the LIAA; and it moves away from the SAA. To investigate what information can be extracted from its evolution, we designed a simple model based on 360-point dipoles evenly distributed in a ring close to the inner core boundary that can be reversed and their magnitude changed. We tried to reproduce with our simple model the observed evolution of the ED, and the total field energy at the Earth’s surface. We observed that the modeled ED moves away from the region where we set the dipoles to reverse. If we consider that the ring dipoles could be related to convective columns in the outer core of the Earth, our simple model would indicate the potential of the displacement of the ED to give information about the regions in the outer core where changes start for polarity transitions and for the generation of important anomalies of the geomagnetic field. According to our simple model, the regions in which the most important events of the Holocene occur, or in which the last polarity reversal or excursion begin, are related to the regions of the Core Mantle Boundary (CMB), where the heat flux is low

A comprehensive multiparametric and multilayer approach to study the preparation phase of large earthquakes from ground to space: The case study of the June 15 2019, M7.2 Kermadec Islands (New Zealand) earthquake

This work deals with a comprehensive multiparametric and multilayer approach to study earthquake-related processes that occur during the preparation phase of a large earthquake. As a case study, the paper investigates the M7.2 Kermadec Islands (New Zealand) large earthquake that occurred on June 15, 2019 as the result of shallow reverse faulting within the Tonga-Kermadec subduction zone. The analyses focused on seismic (earthquake catalogs), atmospheric (climatological archives) and ionospheric data from ground to space (mainly satellite) in order to disclose the possible Lithosphere-Atmosphere-Ionosphere Coupling (LAIC). The ionospheric investigations analysed and compared the Global Navigation Satellite System (GNSS) receiver network with in-situ observations from space thanks to both the European Space Agency (ESA) Swarm constellation and the China National Space Administration (CNSA in partnership with Italian Space Agency, ASI) satellite dedicated to search for possible ionospheric disturbances before medium-large earthquakes, i.e. the China Seismo-Electromagnetic Satellite (CSES-01). An interesting comparison is made with another subsequent earthquake with comparable magnitude (M7.1) that occurred in Ridgecrest, California (USA) on 6 July of the same year but in a different tectonic context. Both earthquakes showed anomalies in several parameters (e.g. aerosol, skin temperature and some ionospheric quantities) that appeared at almost the same times before each earthquake occurrence, evidencing a chain of processes that collectively point to the moment of the corresponding mainshock. In both cases, it is demonstrated that a comprehensive multiparametric and multilayer analysis is fundamental to better understand the LAIC in the occasion of complex phenomena such as earthquakes.This work was undertaken in the framework of Limadou-Science+ funded by ASI (Italian Space Agency). Part of the funds were also given by Working Earth (Pianeta Dinamico) Project. We thank GeoNet (NZ) for providing TEC data (we also thank Claudio Cesaroni and Luca Spogli for giving suggestions on TEC data analyses) and the Kyoto World Data Center for Geomagnetism (http://wdc.kugi.kyoto-u.ac.jp/) for providing geomagnetic data indices. ESA is thanked for providing the Swarm satellite data and the CNSA (Chinese National Space Administration) for providing CSES-01 satellite data

Possible Lithosphere-Atmosphere-Ionosphere Coupling effects prior to the 2018 Mw = 7.5 Indonesia earthquake from seismic, atmospheric and ionospheric data

In this study, we analyse Lithosphere Atmosphere Ionosphere Coupling (LAIC) effects to identify some phenomena that could, possibly, be linked to the preparation phase of the MW=7.5 earthquake occurred in Indonesia on September 28th, 2018, by investigating the eight months preceding the seismic event. First, we find a seismic acceleration that started two months before the mainshock. Then, studying some physical properties of the atmosphere (skin temperature, total column water vapor and aerosol optical thickness), we find two increases of atmospheric anomalies about 6 and 3.7 months before the mainshock, and the latter one is very promising as a candidate for seismic-related phenomena. Furthermore, we investigate ionospheric disturbances, by analysing the Swarm and, for the first time, China Seismo-Electromagnetic Satellite (CSES), magnetic and electron density data during quiet geomagnetic time. From different techniques, we find interesting anomalies concentrated around 2.7 months before the mainshock. On August 19th, 2018, Swarm and CSES showed an enhancement of the electron density during night time. We critically discuss the possibility that such phenomenon can be a possible pre-seismic-induced ionospheric effect. Finally, we performed a cumulative analysis using all detected anomalies, as a test case for a possible chain of physical phenomena that could happen before the earthquake occurrence. With this study, we support the usefulness to collect and store large Earth ground and satellite observational dataset that in the future could be useful to monitor in real time the seismic zones to anticipate earthquakes, although nowadays, there is no evidence about useful prediction capabilities.Published1040972A. Fisica dell'alta atmosferaJCR Journa

Precursory worldwide signatures of earthquake occurrences on Swarm satellite data

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.Publishedid 202872A. Fisica dell'alta atmosferaJCR Journa