EMRP2.12

At present, the geomagnetic observatory at Lampedusa (south of Sicily — Italy, geographic coordinates 35°31′N; 12°32′E, altitude 33 m a.s.l. - provisional IAGA code: LMP) is the southernmost point of observation in European territory, and since 2007 it contributes at filling the spatial observational gap in the whole south Mediterranean and North African areas. A signature of very low electromagnetic noise is expected at LMP, since it is located in the inner part of a wild park with limited access, far away from the urbanized areas of the island. LMP lies in the middle of the Mediterranean Sea, while the other two Italian observatories (Castello Tesino – CTS and Duronia - DUR, in North and central Italy, respectively) are located in the continental territory.

Comparisons among the three observatories, in both time and frequency domains, allow to magnetically characterize the Italian territory. Both 1-minute and 1-second data for the years 2017-2020 are analyzed under a statistical approach and also single event analysis is performed. Superposed Epoch Analysis (SEA) of geomagnetic data from the three observatories returns individual responses to external triggers during geomagnetic storms as well as SSC and SI events, indicating that in correspondence to impulsive inputs a peculiar feature arises at LMP, probably as contribution of electric currents in the surrounding sea salt water. Magnetic responses in the Ultra-Low-Frequency (ULF, 1 mHz–5 Hz) range from spectral, local Signal-to-Noise Ratio (SNR) analyses under different local time are computed, showing that the signal emerges mainly during morning hours, as expected for upstream waves related ULF source waves: in particular, the distinct narrow band characteristic of SNR at LMP indicates that the ULF signals are here mainly uncontaminated by local Field Line Resonance (FLR) as at DUR and CTS, while lower noise levels estimated at LMP suggest a smaller anthropogenic contamination in this frequency range. Moreover, for the first time at such low latitudes in the Mediterranean region, we find evidence of FLR events on Duronia–Lampedusa intermediate field line with the application of the gradient method, a consolidated technique that provides estimates of the ULF standing wave frequencies.. Results from data retrieved by geomagnetic observatories, whose long time series of data are of primary importance, demonstrate a unique contribution in characterizing the magnetospheric response to external events.

How to cite: Di Mauro, D., Regi, M., Lepidi, S., Del Corpo, A., Dominici, G., Bagiacchi, P., Benedetti, G., and Cafarella, L.: Geomagnetic Observatory at Lampedusa Island: Characterization of local magnetic activity and comparison with the other Italian observatories, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9173, https://doi.org/10.5194/egusphere-egu22-9173, 2022.

The spectral method has been widely used in various branches of science since it simplifies the analysis of periodic signals. In the case of geophysics, Fourier transform is used to decompose the signal into different wavelengths, and to associate the gradient of the spectral energy to the depth of the source (after Spector and Grant, 1970). This last association is mostly applied in gravity and magnetism, that is, from sources that produce a contrast of density or magnetic susceptibility with respect to the medium. Large part of the mathematical operators used in geophysics rely on the Fourier analysis.

In this work, we set out an analysis of the spectral energy of the magnetic signal in three and two dimensions. We apply this analysis to three cases: the first case, the classical approach, corresponds to the spectral energy calculated from synthetic magnetic anomalies, produced by bodies of simple geometry. In the second case, we use marine magnetic anomalies on a regional scale, specifically of the Caribbean plate, and finally, a third case, where we apply the method on a marine area covering a few square kilometers. Our objective was primarily to explore and characterize the spectral response from another perspective: that of the spectral cube and to estimate depths of magnetic sources from methods previously used to derive only the depth of the Curie isotherm. A first trial in the application of this method was carried out by Garcia-Reyes and Dyment (2020). However, the application of this in other areas allows evaluating its sensitivity to factors such as scale, resolution and quality of the data, the proximity of the source and geometry of the source. This exercise allows us to validate the approach in estimating depths of sources in the subsurface, and in turn, it is a step forward in understanding the spectral cube and the information it provides.

Our results allow us to offer a mapping of the depth of the magnetic sources (detectable in the spectra), and in turn, a three-dimensional view of their spectral energy. These sources are generally correlated with geological structures, as is the case with the results obtained for the Caribbean plate. Beyond the major developments of the spectral method in geophysics, we suggest that the information inscribed in the spectral signature of magnetic anomalies can still be further explored.

References:

GARCIA-REYES, Andreina and DYMENT, Jérôme (2020). Spatial Power Spectral Density Distribution of Magnetic Sources in the Gulf of Mexico and Caribbean Plate. In : AGU Fall Meeting Abstracts. p. GP012-0009.

Spector, A., & Grant, F. S. (1970). Statistical models for interpreting aeromagnetic data. Geophysics, 35(2), 293-302.

How to cite: Garcia-Reyes, A. and Dyment, J.: Exploration of spectral energy from marine and modeled magnetic anomalies, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10727, https://doi.org/10.5194/egusphere-egu22-10727, 2022.

The paper considers the reason for the displacement of the magnetic axis relative to the axis of rotation of the Earth for the case of the quartz nature of the dipole magnetic field. A model based on a ring with a current with an uneven distribution of charges along the circumference of the ring is considered. It is shown that the magnetic axis shifts from the axis of rotation towards a greater concentration of charges and, conversely, with a decrease in the concentration of charges. The issue of reducing the number of gravity-oriented quartz crystals in areas of volcanic activity is discussed. The temporal correlation of the beginning of accelerated drift of the Earth's north magnetic pole with the development of volcanic and tectonic activity in the Yellowstone caldera is shown. Attention is drawn to the fact that the Earth's north magnetic pole is shifting towards the geographical pole relative to the geographical coordinates of the Yellowstone caldera.

How to cite: Zhumabayev, B. and Vassilyev, I.: The relationship of the displacement of the north magnetic pole with volcanic activity in the Yellowstone caldera, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4530, https://doi.org/10.5194/egusphere-egu22-4530, 2022.

Eccentric dipole can be considered the next approximation of the geomagnetic field after the
generally used geocentric dipole. Considering that during reversals, excursions and important
anomalies the non-dipole contributions are relevant, we study the evolution of the eccentric
dipole during the last reversal (Matuyama-Brunhes transition, ~780 ka), last excursions
(Laschamp, ~41 ka and Mono-Lake, ~34 ka), the Levantine Iron Age Anomaly (LIAA, ~1000 BC)
and the South Atlantic Anomaly (SAA, from 700 AD to present day) according to
paleoreconstructions (IMMAB4, LSMOD.2, SHAWQ-Iron Age and SHAWQ2k, respectively). In
order to get as much as information as possible from the eccentric dipole, we design a simple
model based on 360-point dipoles evenly distributed in a ring close to the Inner Core Boundary
that can be reversed and/or changed their magnitude. We calculate the evolution of the
modeled eccentric dipole according to the 360-dipole ring model reproducing the eccentric
dipole from the paleoreconstructions. If we consider that each point dipole could be associated
to convective columns in the outer core of the Earth, we can relate the evolution of the eccentric
dipole with potential variations in the outer core that cause its displacement. We observe that
the modeled eccentric dipole moves away from regions where dipoles start to reverse (which
are the cases for the reversal, excursions and the SAA) and towards regions where there are
anomalous high-moment dipoles (such as the LIAA). The results show that the eccentric dipole
paths during the events studied correlate well to Core Mantle Boundary low heat flux regions
that is consistent with the development of instabilities in the geomagnetic field.

How to cite: González-López, A., Osete, M. L., A. Campuzano, S., Rivera-Pérez, P., Molina-Cardín, A., and Pavón-Carrasco, F. J.: Analysis of the Last Reversal, Last Excursions and important HoloceneAnomalies of the Geomagnetic Field using the Eccentric Dipole and a 360-Dipole Ring Mode, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8344, https://doi.org/10.5194/egusphere-egu22-8344, 2022.

Computed from the intensity of the globally symmetrical equatorial electrojet (Ring Current) measured by a series of near-equatorial geomagnetic observatories, the Dst (Disturbance Storm Time) is an hourly index of magnetic activity. To give the estimation of the Dst index through the magnetic data measured by the Swarm three-satellite mission, we selected and trained an Artificial Neural Network (ANN). From November 2014 to December 2019, we collected a big Swarm magnetic dataset, confined in space to three very narrow belts of low-to-mid latitude, to better resemble the geographic distribution of the four geomagnetic observatories used to estimate at ground Dst. We also extended the analysis to mid latitude locations to increase the number of satellite samples. By using a Deep Learning architecture and based on its performance, we selected the best topology and trained the network testing its modelling capabilities. The outcomes show that the ANN is able to give a reliable fast estimation of the Dst index directly from Swarm satellite magnetic data, especially during magnetically disturbed periods.

How to cite: Cianchini, G., Piscini, A., De Santis, A., and Arquero Campuzano, S.: Disturbance Storm Time (Dst) index estimation using deep learning applied to Swarm satellite data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5000, https://doi.org/10.5194/egusphere-egu22-5000, 2022.

The cut-off rigidities of cosmic rays usually do not reflect the influence of the crustal geomagnetic field. Due to the weakness of the crustal field effect to the cosmic rays trajectories are very minor. However, two regions of the world have a crustal field with significantly higher values. The effect of the crustal field in those regions is evaluated. The consequences for the approach of cosmic rays to Earth's surface (top of the Earth atmosphere) in the last decades are analyzed and discussed. Presented are suggestions for possible modification of models for evaluation of Earth's magnetosphere transparency for cosmic rays.

How to cite: Jakab, P. and Bobík, P.: The evaluation of crustal field influence to geomagnetic cutt-off rigidities, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3867, https://doi.org/10.5194/egusphere-egu22-3867, 2022.