Home » Geomagnetism

Category Archives: Geomagnetism

Linear vs nonlinear methods for detecting magnetospheric and ionospheric current systems patterns

Papers from SWICo members

T. Alberti, F. Giannattasio, P. De Michelis and G. Consolini.

The geomagnetic field time series can be viewed as a superposition of signals which represent the different contributions to it at different scales coming from various sources both internal and external to the Earth. Here, we apply two different methods of analysis in order to recognize in the magnetic field of external origin the different contributions coming from external sources, making use of measurements of the vertical component of the geomagnetic field (directed away from the Earth’s center) recorded by the European Space Agency (ESA) Swarm A and B satellites at low and mid latitudes during a geomagnetically quiet period.

The main external contributions to the geomagnetic field as reconstructed through the Multivariate Empirical Mode Decomposition (MEMD). From top to bottom: 1) the residue (res) of the MEMD method can be attributed to the ring current contribution; 2) the c5 mode pattern can be related to the main Sq pattern; 3) the c4 mode pattern can be attributed to a sub-harmonic structure of the Sq current; 4) short-scale reconstructions expressed by C1−3 modes could be related to different source mechanisms (external drivers, magnetopause current).

The first is a linear method, that is, the Empirical Orthogonal Functions (EOF); the second is a nonlinear one, i.e. the Multivariate Empirical Mode Decomposition (MEMD). As the external contributions to the magnetic signal are intrinsically nonlinear, the MEMD seems to give better results with respect to EOF, and only five modes and a residue are necessary to reproduce the different contributions coming from the external sources against the 26 modes that are necessary in the case of the EOF. This study is an example of the potential of the MEMD for the analysis of the geomagnetic field of external origin, and of its capability to separate the ionospheric from the magnetospheric contributions in a simple and rapid way.

Publication: T. Alberti, F. Giannattasio, P. De Michelis and G. Consolini, Linear vs nonlinear methods for detecting magnetospheric and ionospheric current systems patterns, Earth and Space Science, 2020.
https://doi.org/10.1029/2019EA000559

On the multifractal features of low-frequency magnetic field fluctuations in the field-aligned current ionospheric polar regions: Swarm observations

Papers from SWICo members

G. Consolini, P. De Michelis, T. Alberti, F. Giannattasio, I. Coco, R. Tozzi, and T. T. S. Chang

In this work we have characterized the magnetic field fluctuations in the high latitude ionosphere by means of high resolution magnetic measurements (50 Hz) from the European Space Agency Earth’s observation mission Swarm.

A sketch of coherent field-aligned flux tubes in a quasi force-free equilibrium. The current is aligned along magnetic structures. The colors refer to different directions of the field-aligned currents.

We found anomalous spatiotemporal scaling features of magnetic field fluctuations in regions where field‐aligned currents occur, at spatial scales in the range 0.8–80 km (timescales in the range 0.1–10 s). The nature of these fluctuations is multifractal, suggesting a highly complex structure of the field‐aligned currents. Our results support the hypothesis that field‐aligned currents are filamentary in nature, and this paves the way to new perspectives in the comprehension of the physical processes responsible for the magnetospheric‐ionospheric coupling.

Publication: G. Consolini, P. De Michelis, T. Alberti, F. Giannattasio, I. Coco, R. Tozzi, and T. T. S. Chang, On the multifractal features of low-frequency magnetic field fluctuations in the field-aligned current ionospheric polar regions: Swarm observations, J. Geophys. Res.: Space Physics, 125, 2020.
https://doi.org/10.1029/2019JA027429

A Preliminary Risk Assessment of Geomagnetically Induced Currents over the Italian Territory

Papers from SWICo members

Authors:
Roberta Tozzi, Paola De Michelis, Igino Coco, Fabio Giannattasio

A sketch representing the chain of events leading to the generation of GICs.

Major geomagnetic storms drive rapid intensification and variability of magnetospheric and ionospheric current systems that give rise to large ground geomagnetically-induced currents (GIC). Space weather associated GIC pose a serious threat to the reliability of power-transmission systems and other electrically conducting infrastructures such as oil and gas pipelines. The most severe effects are observed at high latitudes due to ionospheric currents associated with the aurora. However, as power transmission grid and pipeline infrastructures continue to grow at middle and low-latitudes, GIC hazards are no longer just concerns of high-latitude regions.

On the left: maximum daily GIC indices estimated from CTS geomagnetic data (blue line); thresholds between the different risk levels (coloured dashed lines); monthly averaged sunspot number (grey line). On the right: table of the threat and risk levels.

We provide a preliminary characterisation of the general risk to which the Italian power grid network is exposed. Due to limited direct GIC measurements, a proxy of the geoelectric field is used, i.e. the GIC index. This is calculated for a time interval of approximately 20 years using data from the two longest running Italian magnetic observatories, i.e. Castello Tesino and L’Aquila. Results show that during periods of high geomagnetic activity, potentially detrimental GICs could flow through the power network, especially at the highest Italian latitudes that are characterized by a low conductivity lithosphere.

Publication:  Tozzi, R., De Michelis, P., Coco, I., Giannattasio, F., 2019. A Preliminary Risk Assessment of Geomagnetically Induced Currents over the Italian Territory, Space Weather, 17, 46-58, doi: 10.1029/2018SW002065. https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018SW002065

More information:

http://www.ingv.it/it/newsletter-ingv-n-8-dicembre-2019-anno-xiii/tempeste-solari-quali-sono-i-rischi-che-corriamo-sulla-nostra-terra

http://www.lescienze.it/news/2011/08/11/news/il_ritorno_della_grande_aurora-551058/

https://www.swpc.noaa.gov/content/education-and-outreach