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1.
2.
This paper considers the results of numerical experiments involving POLYMODE data assimilation by a barotropic model for synoptic ocean dynamics. The model's response the data assimilation for various space-time discretenesses of assimilation is studied. Results derived from the application of optimal interpolation algorithms and modified optimal filtration algorithms are compared. Qualitative similarity to the calculations carried out through the simulation modelling technique is noted. Optimal assimilation algorithms are determined, depending on the space-time discreteness used. An optimal sampling discreteness for the POLYMODE conditions is suggested.Translated by Vladimir A. Puchkin. 相似文献
3.
Jeffrey P. Severinghaus Alexi Grachev Nicolas Caillon 《Geochimica et cosmochimica acta》2003,67(3):325-343
We describe a method for measuring the 40Ar/36Ar ratio and the 84Kr/36Ar ratio in air from bubbles trapped in ice cores. These ratios can provide constraints on the past thickness of the firn layer at the ice core site and on the magnitude of past rapid temperature variations when combined with measured 15N/14N. Both variables contribute to paleoclimatic studies and ultimately to the understanding of the controls on Earth’s climate. The overall precision of the 40Ar/36Ar method (1 standard error of the mean) is 0.012‰ for a sample analyzed in duplicate, corresponding to ±0.6 m in reconstructed firn thickness. We use conventional dynamic isotope ratio mass spectrometry with minor modifications and special gas handling techniques designed to avoid fractionation. About 100 g of ice is used for a duplicate pair of analyses. An example of the technique applied to the GISP2 ice core yields an estimate of 11 ± 3K of abrupt warming at the end of the last glacial period 15,000 years ago. The krypton/argon ratio can provide a diagnostic of argon leakage out of the bubbles, which may happen (naturally) during bubble close-off or (artifactually) if samples are warmed near the freezing point during core retrieval or storage. Argon leakage may fractionate the remaining 40Ar/36Ar ratio by +0.007‰ per ‰ change in 84Kr/36Ar, introducing a possible bias in reconstructed firn thickness of about +2 m if thermal diffusion is not accounted for or +6 m if thermal diffusion effects are quantified with measured 15N/14N. Reproducibility of 84Kr/36Ar measured in air is about ±0.2‰ (1 standard error of the mean) but is about ±1‰ for ice core samples. Ice core samples are systematically enriched in 84Kr/36Ar relative to atmosphere by ∼5‰, probably reflecting preferential size-dependent exclusion of the smaller argon atom during bubble entrapment. Recent results from the Siple Dome ice core reveal two climate events during the last deglaciation, including an 18-m reduction in firn thickness associated with an abrupt warming at sometime between 18 and 22 kyr BP and a partial or total removal of the firn during an ablation event at 15.3 kyr BP. 相似文献
4.
A. F. Grachev I. L. Kamensky O. A. Korchagin H. A. Kollmann 《Izvestiya Physics of the Solid Earth》2007,43(9):766-772
The paper presents preliminary results derived from the study of He isotopy in a transitional clay bed at the critical 65-Ma boundary in the Gams area (Eastern Alps). The ratio 3He/4He is shown to decrease from bottom to top of the transitional layer, and the difference between its values in the lower-and uppermost sublayers of the layer exceeds by more than ten times the measurement uncertainty (5%). The ratio 3He/4He is smallest in the upper part of the section, where all features of an impact event (spherules of pure nickel, diamonds, and awaruite) are established. The general inference of our study is that 3He enrichment in the lower part of the Gams section is related not to cosmic matter but to a change in the conditions in the source area, most likely, to volcanic activity. The effect of the latter has been established, independent of He isotopic studies, from anomalous concentrations of As, Pb, Cu, and Zn and from the presence of particles of gold, copper, and titanomagnetite similar in composition to its basaltic varieties. 相似文献
5.
S. I. Grachev 《Astrophysics》2007,50(4):515-524
A new method is proposed to account for multiple scattering by electrons in calculations of the correlation functions describing
the angular fluctuations in the cosmic microwave background radiation (CMBR). The apparatus of the theory of radiative transport
with Rayleigh scattering is used. The problem is reduced to solving an integral equation for the vector source function (dependent
only on time), along with differential equations for the other quantities (scalar potentials, baryon velocities, etc.) which
show up in the problem. The quantities which describe the angular fluctuations in the CMBR (in the temperature and in the
polarization) are then calculated by integrating the vector source function along the line of sight. As an illustration, the
correlation functions and power spectra are calculated for the case where the fluctuations are produced by some initial gaussian
perturbations of the CMBR.
__________
Translated from Astrofizika, Vol. 50, No. 4, pp. 621–631 (November 2007). 相似文献
6.
We have calculated the distortions of the cosmic microwave background (CMB) spectrum in the wavelength range 2–50 cm due to the superposition of the CMB hydrogen recombination radiation in subordinate lines. The level populations were determined by numerically solving the equation of recombination kinetics together with the statistical equilibrium equations for a 60-level model hydrogen atom. The relative distortions are ≈10?7–10?6, with their wavelength dependence having a low-contrast, wavy pattern. However, the contrast increases severalfold and becomes pronounced when passing to the differential distortion spectrum. We study the dependence of the distortions on cosmological parameters. 相似文献
7.
V. I. Slysh M. A. Voronkov V. Migenes K. M. Shibata T. Umemoto V. I. Altunin I. E. Val'Tts B. Z. Kanevsky M. V. Popov A. V. Kovalenko E. B. Fomalont B. A. Poperechenko YU. N. Gorshenkov B. R. Carlson S. M. Dougherty J. E. Reynolds D. R. Jiang A. I. Smirnov V. G. Grachev 《Monthly notices of the Royal Astronomical Society》2001,320(2):217-223
We report on the first space–VLBI observations of the OH 34.26+0.15 maser in two main-line OH transitions at 1665 and 1667 MHz. The observations involved the space radio telescope on board the Japanese satellite HALCA and an array of ground radio telescopes. The map of the maser region and images of individual maser spots were produced with an angular resolution of 1 mas, which is several times higher than the angular resolution available on the ground. The maser spots were only partly resolved and a lower limit to the brightness temperature was obtained. The maser seems to be located in the direction of low interstellar scattering, an order of magnitude lower than the scattering of a nearby extragalactic source and pulsar. 相似文献
8.
The evolution of the spectrum of isotropic uniform radiation in an infinite space filled with a homogeneous, nonrelativistic electron gas is calculated by solving the Kompaneets equation. For an infinitely narrow initial spectrum, the time dependence of the average frequency and frequency dispersion is determined in a linear approximation of the equation. Characteristic times corresponding to changes in the character of this dependence are introduced. Two schemes are proposed for the numerical solution of the nonlinear equation: a nonconservative scheme with a grid that is uniform in frequency and a conservative scheme with automatic selection of an adaptive grid in frequency and time. For the linear equation the method yields results consistent with calculations of its solutions in terms of an eigenfunction expansion of the Kompaneets operator calculated in [D. I. Nagirner and V. M. Loskutov, Astrofizika, 40, 97 (1977)]. The influence of nonlinearity on the evolution of the spectrum of initially monochromatic radiation of various intensities is traced as an example of the application of the method. 相似文献
9.
10.
A. F. Grachev 《Izvestiya Physics of the Solid Earth》2012,48(1):17-27
New data on the chemical composition of ultrapotassic Bar volcanics penetrated by the Bar-6 well are presented. The mineral
compositions are analyzed, and lamproitic affinity of volcanics is established. According to the new K-Ar datings, the volcanics
are not older than 2 Ma. Comparative analysis of Bar volcanic rocks against the ultrapotassic formations of Vardar zone in
Macedonia and in other regions showed that Bar volcanics form the northernmost edge of the zone of ultrapotassic Pliocene-Quaternary
volcanism extending up to southern Macedonia. This zone was formed in conditions of extension, and the volcanism itself was
a result of the melting of the depleted mantle. 相似文献