282 research outputs found
New spectral functions of the near-ground albedo derived from aircraft diffraction spectrometer observations
No full textThe airborne spectral observations of the upward and downward irradiances are
revisited to investigate the dependence of the near-ground albedo as a
function of wavelength in the entire solar spectrum for different surfaces
(sand, water, snow) and under different conditions (clear or cloudy sky). The
radiative upward and downward fluxes were determined by a diffraction
spectrometer flown on a research aircraft that was performing multiple flight
paths near the ground. The results obtained show that the near-ground albedo
does not generally increase with increasing wavelengths for all kinds of
surfaces as is widely believed today. Particularly, in the case of water
surfaces it was found that the albedo in the ultraviolet region is more or
less independent of the wavelength on a long-term basis. Interestingly, in
the visible and near-infrared spectra the water albedo obeys an almost
constant power-law relationship with wavelength. In the case of sand surfaces
it was found that the sand albedo is a quadratic function of wavelength,
which becomes more accurate if the ultraviolet wavelengths are neglected.
Finally, it was found that the spectral dependence of snow albedo behaves
similarly to that of water, i.e. both decrease from the ultraviolet to the
near-infrared wavelengths by 20–50%, despite the fact that their values
differ by one order of magnitude (water albedo being lower). In addition, the
snow albedo vs. ultraviolet wavelength is almost constant, while in the
visible near-infrared spectrum the best simulation is achieved by a
second-order polynomial, as in the case of sand, but with opposite slopes
Erratum: Future temperature extremes will be more harmful: A new critical factor for improved forecasts (Int. J. Environ. Res. Public Health 2019, 16 (20), 4015)
No full textThe authors would like to correct the names and surnames of both authors of their previous paper [1] as follows: Costas A. Varotsos1,2,* and Yuri A. Mazei2 Therefore, to cite this paper please use the correct reference as follows: Varotsos, C.A.; Mazei,Y.A. Future Temperature Extremes Will Be More Harmful: A New Critical Factor for Improved Forecasts. Int. J. Environ. Res. Public Health 2019, 16 (20), 4015. © 2020 by the author. Licensee MDPI, Basel, Switzerland
A new modeling tool for the diffusion of gases in ice or amorphous binary mixture in the polar stratosphere and the upper troposphere
No full textTo elaborate stratospheric ozone depletion processes, measurements of diffusion coefficients of selected gas phase molecules (i.e. HCl, CH<sub>3</sub>OH, HCOOH and CH<sub>3</sub>COOH; Katsambas et al., 1997; Kondratyev and Varotsos, 1996; Varotsos et al., 1994, 1995) in ice in the temperature range 170–195 K have been analyzed with respect to the mechanisms and rates of diffusion. It is argued that the diffusion in ice of these compounds is governed by a vacancy – mediated mechanism, i.e. H<sub>2</sub>O vacancies are required to diffuse to lattice sites adjacent to these compounds prior to the diffusion of the corresponding molecule into the vacancy sites. In addition, we show that the diffusion coefficients of these compounds exhibit a specific interconnection, i.e. a linear relationship holds between the logarithm of the pre-exponential factor, <i>D</i><sub>o</sub>, and the activation energy <i>E</i>. The physical meaning of this interconnection is discussed
Thermodynamic properties of defects in H2O-ICE, NaCl, NaBr Crystals on the basis of bulk elastic data for atmospheric implications
No full textRecently the heterogeneous reactions are increasingly recognized as significant in the atmosphere. In this work the reactions of gases with H20-ice, solid NaCI and solid NaBr crystals at temperatures 250 K and 273 K were examined by using a recently proposed thermodynamical model (Varotsos et. al., 1988) which provides the interconnection of entropy and enthalpy for various processes with well known macroscopic properties of the bulk solid. © 1993, Taylor &amp; Francis Group, LLC. All rights reserved
Calculation of point defect parameters in diamond
No full textWe show that the most recent values of the defect entropy and the defect enthalpy for the vacancy formation in diamond have a ratio which is comparable to the one predicted by a model suggested three decades ago [P. Varotsos and K. Alexopoulos, Phys. Rev. B 15, 4111 (1977); 18, 2683 (1978)]. This model, which interconnects the formation Gibbs energy with the bulk elastic and expansivity data, has been also recently found of value in high T-c superconductors as well as in glass-forming liquids
On the role of solid NaCl in polluted marine urban areas
No full textLast decade the reactions of gases at solid interfaces were increasingly recognized as significant in polluted marine troposphere and perhaps in remote areas as well. In this study the reactions of gases with solid NaCl at temperatures 200 K and 300 K were examined by using a recently proposed thermodynamical model (Varotsos et al., 1988) which provides the interconnection of entropy and enthalpy for various processes with well known macroscopic properties of the bulk solid. © 1994, Taylor & Francis Group, LLC. All rights reserved
On the role of solid nabr in the atmosphere after the eruption of alkalic volcanoes
No full textVarious atmospheric gases may react with solid NaCl and NaBr in sea salt particles in polluted marine areas, as well as in the Arctic. The affinity of these gases for the solid NaBr is confined to a surface layer that is at least several hundred angstroms deep. It has been shown that these reactions are mostly likely associated among others with crystal defects. In this study the heterogeneous reactions of various gases with solid NaBr were examined by using a recently proposed model (Varotsos et al., 1988). © 1994, Taylor & Francis Group, LLC. All rights reserved
Self-diffusion in sodium under pressure revisited
No full textThe pressure - volume relation in sodium has been measured up to 100 GPa using high-resolution angle-dispersive synchrotron x-ray diffraction (Hanfland et al 2002 Phys. Rev. B 65 184109). In the light of these data, we show that a model suggested long ago (e.g., Varotsos et al 1978 J. Phys. C: Solid State Phys. 11 L305 - 15) can satisfactorily answer the long-standing question of the variation of the diffusion coefficient D under pressure P, which resulted in a curved ln D versus P plot, in the frame of a single operating mechanism (monovacancies). This is achieved without using any adjustable parameters
M W9 Tohoku earthquake in 2011 in Japan: precursors uncovered by natural time analysis
No full textThis paper reviews the precursory phenomena of the 2011 MW9 Tohoku earthquake in Japan that emerge solely when we analyze the seismicity data in a new time domain termed natural time. If we do not consider this analysis, important precursory changes cannot be identified and hence are missed. Natural time analysis has the privilege that enables the introduction of an order parameter of seismicity. In this frame, we find that the fluctuations of this parameter exhibit an unprecedented characteristic change, i.e., an evident minimum, approximately two months before Tohoku earthquake, which strikingly is almost simultaneous with unique anomalous geomagnetic field variations recorded mainly on the z component. This is consistent with our finding that such a characteristic change in seismicity appears when a seismic electric signal (SES) activity of the VAN method (from the initials of Varotsos, Alexopoulos, Nomicos) initiates, and provides a direct confirmation of the physical interconnection between SES and seismicity. © 2017, The Author(s)
Migration and activation defect volumes in CdF2
No full textIn 1980 Oberschmidt and Lazarus studied the ionic conductivity of CdF2 under various pressures and determined the migration volume for the free-anion-vacancy motion. In a recent study Samara confirmed the results of Oberschmidt and Lazarus and emphasized that the so-called strain-energy model of Keyes et al. fails to reproduce the experimental values. The latter are shown to be in accordance with another thermodynamical model suggested by Varotsos and Alexopoulos. This model is found to give also the correct values for the activation volumes determined from recent high-pressure studies of the association region of the dc conductivity curve of CdF2 doped with various alkali metals. The present paper provides the first application of the above thermodynamical model to cases where the activation volumes contain contributions from migration and association processes. © 1985 The American Physical Society
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