scholarly journals The ultra low frequency electromagnetic radiation observed in the topside ionosphere above boundaries of tectonic plates

2015 ◽  
Vol 4 (1) ◽  
Author(s):  
Michael A. Athanasiou ◽  
Gergios C. Anagnostopoulos ◽  
Constantinos N. David ◽  
Gregorios G. Machairides
Keyword(s):  
Electromagnetic Radiation ◽  
Seismic Activity ◽  
Eastern Mediterranean ◽  
Singular Spectrum Analysis ◽  
Low Frequency ◽  
Topside Ionosphere ◽  
Tectonic Plates ◽  
Electromagnetic Emissions ◽  
Eastern Mediterranean Basin ◽  
Electric Field Instrument

In this paper we present results of a comparison between ultra low frequency (ULF) electromagnetic (EM) radiation, recorded by an electric field instrument onboard the satellite detection of electromagnetic emissions transmitted from earthquake regions in the topside ionosphere, and the seismicity of regions with high and low seismic activity. In particular, we evaluated the energy variations of the ULF Ezelectric field component during a period of four years (2006-2009), in order to examine the possible relation of ULF EM radiation with seismogenic regions located in Central America, Indonesia, the Eastern Mediterranean Basin and Greece. As a tool for evaluating the ULF Ez energy variations we used singular spectrum analysis techniques. The results of our analysis clearly show a significant increase of the ULF EM energy emitted from regions of highest seismic activity at the boundaries tectonic plates. Furthermore, we found that higher electromagnetic radiation was detected in a region above the northern- western Greek Arc (R1) than above the adjacent region including Athens and its urban area. We interpret these results of the present study as suggesting that: i) the seismogenic regions at the boundary of tectonic plates radiate ULF EM emissions observed by satellites in the topside ionosphere; and ii) that this EM radiation is not only related with the occurrence time of great (M≥5) earthquakes, but it is often present in intermediate times and it appears as a quasi-permanent phenomenon.

scholarly journals From high temporal resolution to synthetically enhanced radiometric resolution: insights from Night Thermal Gradient results

2021 ◽  
Vol 230 (1) ◽  
pp. 111-132 ◽  
Author(s):  
L. Piroddi
Keyword(s):  
Data Processing ◽  
Temporal Resolution ◽  
Seismic Activity ◽  
Thermal Gradient ◽  
Central Italy ◽  
Low Frequency ◽  
Thermal Infrared ◽  
High Temporal Resolution ◽  
Electromagnetic Emissions ◽  
Frequency Components

Abstract Electromagnetic emissions in thermal infrared bands are an important research topic on pre-earthquake studies. Satellite thermal data have been investigated by many independent research groups looking for their anomalous behaviour before main earthquake's occurrences. Among them, geosynchronous satellite data are reported as less prone to artefacts during data processing. In this work, the Night Thermal Gradient (NTG) algorithm is presented, which has been specifically proposed for geostationary thermal infrared data processing. NTG method relies on the exploitation of high temporal resolution data to find coherent low frequency components of a hypothetical precursory signal of seismic activity. In this paper, the method is presented by giving details about the applied procedures, steps, theoretical assumptions and results obtained during the studies of L'Aquila 2009 earthquake and the seismic activity of Central Italy and Sardinia.

scholarly journals Low-frequency current variability at the Straits of Crete, eastern Mediterranean

1997 ◽  
Vol 102 (C11) ◽  
pp. 25005-25020 ◽  
Author(s):  
M. N. Tsimplis ◽  
A. F. Velegrakis ◽  
A. Theocharis ◽  
M. B. Collins
Keyword(s):  
Eastern Mediterranean ◽  
Low Frequency ◽  
Frequency Current

scholarly journals Empirical Mode Reduction in a Model of Extratropical Low-Frequency Variability

2006 ◽  
Vol 63 (7) ◽  
pp. 1859-1877 ◽  
Author(s):  
D. Kondrashov ◽  
S. Kravtsov ◽  
M. Ghil
Keyword(s):  
Numerical Study ◽  
Singular Spectrum Analysis ◽  
Low Frequency ◽  
The Arctic ◽  
Reduced Model ◽  
The North ◽  
Low Frequency Variability ◽  
Intraseasonal Oscillations ◽  
The Arctic Oscillation ◽  
The North Atlantic Oscillation

Abstract This paper constructs and analyzes a reduced nonlinear stochastic model of extratropical low-frequency variability. To do so, it applies multilevel quadratic regression to the output of a long simulation of a global baroclinic, quasigeostrophic, three-level (QG3) model with topography; the model's phase space has a dimension of O(104). The reduced model has 45 variables and captures well the non-Gaussian features of the QG3 model's probability density function (PDF). In particular, the reduced model's PDF shares with the QG3 model its four anomalously persistent flow patterns, which correspond to opposite phases of the Arctic Oscillation and the North Atlantic Oscillation, as well as the Markov chain of transitions between these regimes. In addition, multichannel singular spectrum analysis identifies intraseasonal oscillations with a period of 35–37 days and of 20 days in the data generated by both the QG3 model and its low-dimensional analog. An analytical and numerical study of the reduced model starts with the fixed points and oscillatory eigenmodes of the model's deterministic part and uses systematically an increasing noise parameter to connect these with the behavior of the full, stochastically forced model version. The results of this study point to the origin of the QG3 model's multiple regimes and intraseasonal oscillations and identify the connections between the two types of behavior.

Effect of low frequency electromagnetic radiation on early growth of sunflower plants

2015 ◽  
Vol 208 ◽  
pp. S109
Author(s):  
Daniel Dorin Dicu ◽  
Paul Pîrşan ◽  
Branko Marinković ◽  
Florin Imbrea ◽  
Simona Niţă
Keyword(s):  
Electromagnetic Radiation ◽  
Low Frequency ◽  
Early Growth

scholarly journals Circulation Regimes and Low-Frequency Oscillations in the South Pacific Sector

2003 ◽  
Vol 131 (8) ◽  
pp. 1566-1576 ◽  
Author(s):  
Andrew W. Robertson ◽  
Carlos R. Mechoso
Keyword(s):  
Singular Spectrum Analysis ◽  
Low Frequency ◽  
South Pacific ◽  
Stationary Wave ◽  
Gaussian Mixture ◽  
Reanalysis Data ◽  
Oscillatory Behavior ◽  
South American ◽  
The South ◽  
Austral Spring

Abstract The characteristics of subseasonal circulation variability over the South Pacific are examined using 10-day lowpass-filtered 700-hPa geopotential height NCEP–NCAR reanalysis data. The extent to which the variability in each season is characterized by recurrent geographically fixed circulation regimes and/or oscillatory behavior is determined. Two methods of analysis (a K-means cluster analysis and a cross-validated Gaussian mixture model) both indicate three to four geographically fixed circulation regimes in austral fall, winter, and (to some extent) spring. The spatial regime structures are found to be quite similar in each season; they resemble the so-called Pacific–South American (PSA) patterns discussed in previous studies and often referred to as PSA 1 and PSA 2. Oscillatory behavior is investigated using singular spectrum analysis. This identifies a predominantly stationary wave with a period of about 40 days and a spatial structure similar to PSA 1; it is most pronounced in winter and spring and exhibits a noticeable eastward drift as it decays. The power spectrum of variability is otherwise well approximated by a red spectrum, together with enhanced broader-band 15–30-day variability. The results presented herein indicate that low-frequency variability over the South Pacific is not dominated by a propagating wave whose quadrature phases are PSA 1 and PSA 2, as hitherto described. Rather, it is found that the variability is well described by the occurrence of three to four geographically fixed circulation regimes, with a (near) 40-day oscillation that is predominantly stationary in space. The potential subseasonal predictability implied by this duality is discussed. Only during austral spring is a strong correlation found between El Niño and the frequency of occurrence of the circulation regimes.

Sensitivity analysis of CDOM spectral slope in artificial and natural samples: an application in the central eastern Mediterranean Basin

2010 ◽  
Vol 72 (4) ◽  
pp. 485-498 ◽  
Author(s):  
Luca Bracchini ◽  
Antonio Tognazzi ◽  
Arduino Massimo Dattilo ◽  
Franco Decembrini ◽  
Claudio Rossi ◽  
...  
Keyword(s):  
Sensitivity Analysis ◽  
Mediterranean Basin ◽  
Eastern Mediterranean ◽  
Spectral Slope ◽  
Eastern Mediterranean Basin ◽  
Central Eastern

scholarly journals Natural variability and anthropogenic effects in a Central Mediterranean core

2012 ◽  
Vol 8 (2) ◽  
pp. 831-839 ◽  
Author(s):  
S. Alessio ◽  
G. Vivaldo ◽  
C. Taricco ◽  
M. Ghil
Keyword(s):  
Isotopic Ratio ◽  
Forecast Error ◽  
Singular Spectrum Analysis ◽  
Low Frequency ◽  
Natural Variability ◽  
Central Mediterranean ◽  
Spectral Content ◽  
Frequency Components ◽  
Oxygen Isotopic ◽  
Complete Series

Abstract. We evaluate the contribution of natural variability to the modern decrease in foraminiferal δ18O by relying on a 2200-yr-long, high-resolution record of oxygen isotopic ratio from a Central Mediterranean sediment core. Pre-industrial values are used to train and test two sets of algorithms that are able to forecast the natural variability in δ18O over the last 150 yr. These algorithms are based on autoregressive models and neural networks, respectively; they are applied separately to each of the δ18O series' significant variability components, rather than to the complete series. The separate components are extracted by singular-spectrum analysis and have narrow-band spectral content, which reduces the forecast error. By comparing the sum of the predicted low-frequency components to its actual values during the Industrial Era, we deduce that the natural contribution to these components of the modern δ18O variation decreased gradually, until it reached roughly 40%, as early as the end of the 1970s.

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