25 research outputs found
Possible Estimation of the Solar Cycle Characteristic Parameters by the 10.7 cm Solar Radio Flux
No full textTwo independent methods for estimating basic parameters of the solar cycle are presented. The first of them, the ascending-descending triangle method, is based on a previous work by Tritakis (Astrophys. Space Sci.82, 463, 1982), which described how the fundamental parameters of a certain solar cycle could be predicted from the shape of the previous one. The relation between the two cycles before and after a specific 11-year solar cycle is tighter than between the two cycles belonging to the same 22-year solar cycle (even-odd cycle). The second is the MinimaxX method, which uses a significant relation in the international sunspot number between the maximum value of a solar cycle and its value 2.5 or 3 years (depending on the enumeration of the even or odd cycle) before the preceding minimum. The tests applied to Cycles 12 to 24 indicate that both methods can estimate the peak of the 11-year solar radio flux at a high confidence level. The data used in this study are the 10.7 cm solar radio flux since 1947, which have been extrapolated back to 1848 from the strong correlation between the monthly international sunspot numbers and the adjusted values of the 10.7 cm radio flux. © 2016, Springer Science+Business Media Dordrecht
Confirmation of an early estimation for an increase in the seismic activity towards the end of the twentieth century
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Inner plasma structure of the low-latitude reconnection layer
No full textWe report a clear transition through a reconnection layer at the low-latitude magnetopause which shows a complete traversal across all reconnected field lines during northwestward interplanetary magnetic field (IMF) conditions. The associated plasma populations confirm details of the electron and ion mixing and the time history and acceleration through the current layer. This case has low magnetic shear with a strong guide field and the reconnection layer contains a single density depletion layer on the magnetosheath side which we suggest results from nearly field-aligned magnetosheath flows. Within the reconnection boundary layer, there are two plasma boundaries, close to the inferred separatrices on the magnetosphere and magnetosheath sides (Ssp and Ssh) and two boundaries associated with the Alfvén waves (or Rotational Discontinuities, RDsp and RDsh). The data are consistent with these being launched from the reconnection site and the plasma distributions are well ordered and suggestive of the time elapsed since reconnection of the field lines observed. In each sub-layer between the boundaries the plasma distribution is different and is centered around the current sheet, responsible for magnetosheath acceleration. We show evidence for a velocity dispersion effect in the electron anisotropy that is consistent with the time elapsed since reconnection. In addition, new evidence is presented for the occurrence of partial reflection of magnetosheath electrons at the magnetopause current layer
Possible east side predominance of the optical emissions of the solar corona
No full textA long term analysis of the green and the red line intensities of the emitting solar corona as well as the polarization of the white corona, which have been compiled by the Pic-du-Midi, Kislovodsk, Irkutsk and Lomnisky Styt observatories, has led to some very interesting results. A prominent East-West asymmetry is obvious in most of the data while a very characteristic seasonal variation of this asymmetry with maxima close to December and minima in July-August is also present. All the errors involved in coronal optical measurements have been examined in a previous paper but none of them have been underlined as the possible cause of the east-west asymmetry. In such a case, the presence of this asymmetry should not be ignored while the reason for its existence should be studied, extensively. Two approximations to a possible explanation of the solar E-W asymmetries have been reported in the discussion section of this article. (C) 1997 Elsevier Science B.V
Possible earthquake forecasting in a narrow space-time-magnitude window
No full textWe analyzed an extended time series of Schumann Resonance recordings with two multi-parametric statistical methods, the generalized linear Logistic Regression—LogReg and the non-linear Random Forest—RF, in order to test their potential for earthquake prediction within a narrow time-space-magnitude window of 48 h, 250 km from our observing site, and events higher than magnitude 4 of the Richter scale. The LogReg method identified the power of the signal within our 10-min recording intervals as the main seismic precursor parameter. The RF method obtained promising results that will improve with continuous enrichment of the running data sample with new data. We conclude that a systematic analysis of Schumann Resonance recordings may lead to satisfactory levels of seismic prediction. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature
Anthropogenic Noise and Its Footprint on ELF Schumann Resonance Recordings
No full textA set of various short artificial disturbances from rifle firings, car engine operation, car radio, shakings of the apparatus, etc., were generated deliberately near our ELF recording stations in order to identify their footprint on the recordings of atmospheric electromagnetic radiation in the Schumann resonance (SR) band (from about 2–50 Hz). Such disturbances simulate anthropogenic noises from hunters, hikers, campers, etc., which may occur in a remote-isolated ELF recording station. We expect that our work will assist fellow scientists to differentiate between artificial signals created from anthropogenic activity and real signals attributable to geophysical phenomena
Design and implementation of a test fixture for ELF schumann resonance magnetic antenna receiver and magnetic permeability measurements
No full textThis paper presents a prototype test fixture for the absolute calibration and estimation of the equivalent magnetic flux noise of the extremely low frequency (ELF) Schumann resonant (SR) magnetic antenna receiver and rods’ magnetic permeability measurement. The test fixture, for ELF the SR detector’s calibration, consists of a constructed coil, the signal generator, and the oscilloscope. The ELF SR detector used has been operating since 2016 near the Doliana village in the Ioannina prefecture, Northwestern Greece. At precisely this spot, far away from electromagnetic noise, the whole setup and experiment took place. The experiments performed with the proposed test fixture showed a sensitivity of 70 nV/pT/Hz and an apparent magnetic permeability at around 250 for the magnetic antenna. The total sensitivity of the ELF receiver was 210 mV/pT near 20 Hz, while the total input noise was around 0.04 pT. © 2020 by the authors. Licensee MDPI, Basel, Switzerland
Pre-seismic Electromagnetic Perturbations in Two Earthquakes in Northern Greece
No full textTwo medium-magnitude earthquakes separated by a distance of 230 km occurred within 34 days from each other in Northern Greece. A few hours before the manifestation of seismic activity, significant extra-low-frequency (ELF) perturbations were detected in a nearby Schumann resonance observation site. The typical spectrum of ELF measurements was deformed with the appearance of an enhanced spectral feature in the frequency range 20–25 Hz. A logit regression model was applied to the data to examine whether ELF perturbations could be considered as precursors of seismic activity. In general, two earthquakes so close to each other (in space, time, and magnitude) form a unique opportunity for the study of characteristic features of pre-seismic ultra-low-frequency (ULF)/ELF perturbations. Quantitative results from a simple nonlinear statistical model support the idea that there is some kind of physical interaction between seismic and atmospheric ELF activities, and that ELF measurements could potentially be used as a useful tool in the forecasting of seismic activity. © 2019, Springer Nature Switzerland AG
Occupational exposure in Greek industrial radiography laboratories (1996-2003)
No full textMore than 40 industrial radiography laboratories are operating in Greece using X-ray or gamma-ray sources and more than 250 workers occupationally exposed to ionising radiation in these facilities are monitored on a regular basis. This study presents the evolution of individual doses received by radiographers during the past years. The mean annual dose (MAD) of all workers as well as of exposed workers is estimated, and correlated to the types of laboratories and practices applied. The MAD of the exposed workers in industrial radiography is compared with the doses of workers in other specialties and with the doses of radiographers in other countries. Furthermore, the study attempts to propose dose constraints for the practices in industrial radiography, according to the BSS European directive and the relevant Greek radiation protection legislation. The proposed value was defined as the dose below which the annual doses of 75% of the exposed radiographers are expected to be included. © 2006 Oxford University Press
