Atmospheric and Coupled Model Intercomparison in Terms of Amplitude—Phase Characteristics of Surface Air Temperature Annual Cycle     

Alexey V. ELISEEV  Igor I. MOKHOV  Konstantin G. RUBINSTEIN  Maria S. GUSEVA 《大气科学进展》2004,(6)

1. Introduction In spite of the progress achieved in global climatemodelling during the last few decades, the models stillshow considerable errors even for the surface air tem-perature ?eld (Covey et al., 2000; IPCC, 2001; Lam-bert and Boer, 2001). As i…  相似文献   

Atmosphere-ionosphere response to the M9 Tohoku earthquake revealed by multiinstrument space-borne and ground observations： Preliminary results     

Dimitar Ouzounov  Sergey Pulinets  Alexey Romanov  Alexander Romanov  Konstantin Tsybulya  Dmitri Davidenko  Menas Kafatos  Patrick Taylor 《地震学报(英文版)》2011,(6):557-564

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Reindeer in tundra ecosystems: the challenges of understanding system complexity     

Feodor V. Kryazhimskii  Alexey N. Danilov 《Polar research》2000,19(1):107-110

The resilience of tundra ecosystems is limited, with relatively few key biotic components determining the general pattern of the dynamics of these systems. Sustainable use of reindeer pastures, which are natural tundra ecosystems, should take into account interactions within the whole complex of key components. Among the most important are the small herbivorous rodents. For example, during peak densities lemmings may reduce above-ground plant biomass by 50-70%. At the same time, rapid turnover of nutrients in the form of significant amounts of potassium, phosphorus and nitrogen that lemmings excrete in urine promotes vascular plant growth. It is concluded that these kinds of studies are essential for the sustainable management of Russia's grazing lands: 1) comparative studies of productivity, biological diversity and structure of plant communities under the different pressures exerted by the main groups of herbivorous animals (reindeer and small rodents), as well as under varying levels of industrial development; 2) studies of the direct and indirect effects of herbivorous mammals on biological turnover and energy flow within the system; 3) studies of the role of industrial contamination on the turnover of nutrients in tundra ecosystems.  相似文献   

Shifted hyperbola moveout approximation revisited     

Alexey Stovas  Sergey Fomel 《Geophysical Prospecting》2012,60(3):395-399

The shifted hyperbola approximation is widely used in seismic applications. Mostly, this approximation is applied to reflection moveout in multilayered media. The traditional domain for this application is the t ‐ x domain. In this paper, we discuss the use of this approximation in the τ ‐ p and t ‐ p domains. The accuracy of the shifted hyperbola approximation defined in different domains is illustrated by analytical and numerical examples.  相似文献   

Constraining dark matter properties with SPI     

Alexey Boyarsky  Denys Malyshev †  rey Neronov  Oleg Ruchayskiy 《Monthly notices of the Royal Astronomical Society》2008,387(4):1345-1360

Using the high-resolution spectrometer SPI on board the International Gamma-Ray Astrophysics Laboratory ( INTEGRAL ), we search for a spectral line produced by a dark matter (DM) particle with a mass in the range  40 keV < M _DM < 14 MeV  , decaying in the DM halo of the Milky Way. To distinguish the DM decay line from numerous instrumental lines found in the SPI background spectrum, we study the dependence of the intensity of the line signal on the offset of the SPI pointing from the direction toward the Galactic Centre. After a critical analysis of the uncertainties of the DM density profile in the inner Galaxy, we find that the intensity of the DM decay line should decrease by at least a factor of 3 when the offset from the Galactic Centre increases from 0° to 180°. We find that such a pronounced variation of the line flux across the sky is not observed for any line, detected with a significance higher than 3σ in the SPI background spectrum. Possible DM decay origin is not ruled out only for the unidentified spectral lines, having low (∼3σ) significance or coinciding in position with the instrumental ones. In the energy interval from 20 keV to 7 MeV, we derive restrictions on the DM decay line flux, implied by the (non-)detection of the DM decay line. For a particular DM candidate, the sterile neutrino of mass M _DM, we derive a bound on the mixing angle.  相似文献   

Constraints on decaying dark matter from XMM–Newton observations of M31     

Alexey Boyarsky  Dmytro Iakubovskyi  Oleg Ruchayskiy  Vladimir Savchenko 《Monthly notices of the Royal Astronomical Society》2008,387(4):1361-1373

We derive constraints on the parameters of the radiatively decaying dark matter (DM) particle, using the XMM–Newton EPIC spectra of the Andromeda galaxy (M31). Using the observations of the outer (5–13 arcmin) parts of M31, we improve the existing constraints. For the case of sterile neutrino DM, combining our constraints with the latest computation of abundances of sterile neutrinos in the Dodelson–Widrow (DW) scenario, we obtain the lower mass limit   m _s < 4 keV  , which is stronger than the previous one   m _s < 6 keV  , obtained recently by Asaka, Laine & Shaposhnikov. Comparing this limit with the most recent results on Lyman α forest analysis of Viel et al.  ( m _s > 5.6 keV  ), we argue that the scenario in which all the DM is produced via the DW mechanism is ruled out. We discuss, however, other production mechanisms and note that the sterile neutrino remains a viable candidate for DM, either warm or cold.  相似文献   

The offset‐midpoint travel‐time pyramid for P‐wave in 2D transversely isotropic media with a tilted symmetry axis          下载免费PDF全文

Qi Hao  Alexey Stovas 《Geophysical Prospecting》2015,63(3):587-596

For pre‐stack phase‐shift migration in homogeneous isotropic media, the offset‐midpoint travel time is represented by the double‐square‐root equation. The travel time as a function of offset and midpoint resembles the shape of Cheops’ pyramid. This is also valid for transversely isotropic media with a vertical symmetry axis. In this study, we extend the offset‐midpoint travel‐time pyramid to the case of 2D transversely isotropic media with a tilted symmetry axis. The P‐wave analytical travel‐time pyramid is derived under the assumption of weak anelliptical property of the tilted transverse isotropy media. The travel‐time equation for the dip‐constrained transversely isotropic model is obtained from the depth‐domain travel‐time pyramid. The potential applications of the derived offset‐midpoint travel‐time equation include pre‐stack Kirchhoff migration, anisotropic parameter estimation, and travel‐time calculation in transversely isotropic media with a tilted symmetry axis.  相似文献   

On shear‐wave triplications in a multilayered transeversely isotropic medium with vertical symmetry axis     

Yuriy Roganov  Alexey Stovas 《Geophysical Prospecting》2010,58(4):549-559

The presence of triplications (caustics) can be a serious problem in seismic data processing and analysis. The traveltime curve becomes multi‐valued and the geometrical spreading correction factor tends to zero due to energy focusing. We analyse the conditions for the qSV‐wave triplications in a homogeneous transversely isotropic medium with vertical symmetry axis. The proposed technique can easily be extended to the case of horizontally layered vertical symmetry axis medium. We show that the triplications of the qSV‐wave in a multilayered medium imply certain algebra. We illustrate this algebra on a two‐layer vertical symmetry axis model.  相似文献   

Applied Mathematics in EM Studies with Special Emphasis on an Uncertainty Quantification and 3-D Integral Equation Modelling   总被引：1，自引：0，他引：1  

Oleg Pankratov  Alexey Kuvshinov 《Surveys in Geophysics》2016,37(1):109-147

Despite impressive progress in the development and application of electromagnetic (EM) deterministic inverse schemes to map the 3-D distribution of electrical conductivity within the Earth, there is one question which remains poorly addressed—uncertainty quantification of the recovered conductivity models. Apparently, only an inversion based on a statistical approach provides a systematic framework to quantify such uncertainties. The Metropolis–Hastings (M–H) algorithm is the most popular technique for sampling the posterior probability distribution that describes the solution of the statistical inverse problem. However, all statistical inverse schemes require an enormous amount of forward simulations and thus appear to be extremely demanding computationally, if not prohibitive, if a 3-D set up is invoked. This urges development of fast and scalable 3-D modelling codes which can run large-scale 3-D models of practical interest for fractions of a second on high-performance multi-core platforms. But, even with these codes, the challenge for M–H methods is to construct proposal functions that simultaneously provide a good approximation of the target density function while being inexpensive to be sampled. In this paper we address both of these issues. First we introduce a variant of the M–H method which uses information about the local gradient and Hessian of the penalty function. This, in particular, allows us to exploit adjoint-based machinery that has been instrumental for the fast solution of deterministic inverse problems. We explain why this modification of M–H significantly accelerates sampling of the posterior probability distribution. In addition we show how Hessian handling (inverse, square root) can be made practicable by a low-rank approximation using the Lanczos algorithm. Ultimately we discuss uncertainty analysis based on stochastic inversion results. In addition, we demonstrate how this analysis can be performed within a deterministic approach. In the second part, we summarize modern trends in the development of efficient 3-D EM forward modelling schemes with special emphasis on recent advances in the integral equation approach.  相似文献   

Abrupt transition from fractional crystallization to magma mixing at Gorely volcano (Kamchatka) after caldera collapse     

Maxim Gavrilenko  Alexey Ozerov  Philip R. Kyle  Michael J. Carr  Alex Nikulin  Christopher Vidito  Leonid Danyushevsky 《Bulletin of Volcanology》2016,78(7):47

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