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排序方式: 共有239条查询结果,搜索用时 15 毫秒
41.
Nikolay G. Granin Sergey I. Muyakshin Mikhail M. Makarov Konstantin M. Kucher Il’ya A. Aslamov Liba Z. Granina Igor B. Mizandrontsev 《Geo-Marine Letters》2012,32(5-6):427-436
Methane bubble fluxes in gas flares from bottom sediments in Lake Baikal were estimated for the first time using hydroacoustic methods. Earlier work has demonstrated the occurrence of gas seeps both inside and outside of areas where bottom simulating reflectors were identified in seismic profiles. Fluxes ranged from 14 to 216 tons per year, with the flux for the entire area of the central and southern basins ranging from 1,400 to 2,800 tons per year. Comparison with other water bodies showed that fluxes from the most intensive Baikal flares were similar to those in the Norwegian and Okhotsk seas. Gas hydrates decompose at the lower boundary of the gas hydrate stability zone due to sedimentation. Calculation of the amount of methane produced due to sedimentation gave a total of between 2,600 and 14,000 tons per year for the central and southern basins of the lake. Based on rough estimation, the total flux from shallow- and deep-water gas seeps is similar to the amount of methane produced due to sedimentation. This suggests that gas hydrates possibly occupy much more than 10?% of the pore volume near the base of the gas hydrate stability zone, or that there are other reasons for gas hydrate dissociation and bubble flux from these bottom sediments. 相似文献
42.
Igor A. Dmitrenko Sergey A. Kirillov Thomas Krumpen Mikhail Makhotin E. Povl Abrahamsen Sascha Willmes Ekaterina Bloshkina Jens A. Hölemann Heidemarie Kassens Carolyn Wegner 《Continental Shelf Research》2010
This paper examines the role of atmospheric forcing in modifying the pathways of riverine water on the Laptev Sea shelf, using summer-to-winter hydrographic surveys from 2007 to 2009. Over the two consecutive winter seasons of 2007–2008 and 2008–2009 in the area of the winter coastal polynya, our data clearly link winter surface salinity fields to the previous summer conditions, with substantially different winter salinity patterns preconditioned by summer atmospheric forcing. In the summer of 2007, dominant along-shore westerly winds in the cyclonic regime force the Lena River runoff to flow eastward. In contrast, in the summer of 2008, dominant along-shore easterly winds over the East Siberian Sea and on-shore northerly winds over the Laptev Sea in the anticyclonic regime lock the riverine water in the vicinity of the Lena Delta. Over the coastal polynya area in the southeastern Laptev Sea these patterns precondition a surface salinity difference of 8–16 psu between the winters of 2008 and 2009. Overall, this indicates a residence time of at least half a year for riverine water on the Laptev Sea shelf. Future climate change associated with an enhanced summer cyclonicity over the eastern Arctic may turn more riverine water eastward along the eastern Siberian coast, resulting in weaker vertical density stratification over the Laptev Sea shelf, with possible impact on the efficiency of vertical mixing and polynya dense water production. 相似文献
43.
Mikhail A. Nosov Anastasia V. Moshenceva Sergey V. Kolesov 《Pure and Applied Geophysics》2013,170(9-10):1647-1660
Because it is based on an initial seismic analysis and preset criteria, tsunami forecast often fails in assessment of tsunami danger. The level of danger can be determined more or less reliably only when observed sea level data became available. Along with the sea level data, i.e., vertical motions of free water surface, we suggest considering horizontal motions of water that accompany the formation and the propagation of a tsunami. The amplitude of horizontal motions is normally much higher than the amplitude of the vertical motions. Detection of the horizontal motions may provide tsunami warning centers with additional in situ data that can be used for estimation of tsunami strength. In this study, taking the 2011 Tohoku-Oki event as an example, horizontal motions of water in the vicinity of the tsunami source are theoretically examined by means of dynamic and static numerical models developed within the framework of linear shallow-water approximation. It is shown that in the vicinity of the tsunami source within a wide area of about 0.5 million square kilometers, the amplitude of horizontal motions exceeded 10 m, whereas in some shallow-water areas the amplitude amounted to hundreds of meters. Possible methods of in situ detection of the horizontal motions are discussed. 相似文献
44.
Mikhail S. Dubovikov 《地球物理与天体物理流体动力学》2013,107(1):19-47
In the framework of the eddy dynamic model developed in two previous papers (Dubovikov, M.S., Dynamical model of mesoscale eddies, Geophys. Astophys. Fluid Dyn., 2003, 97, 311–358; Canuto, V.M. and Dubovikov, M.S., Modeling mesoscale eddies, Ocean Modelling, 2004, 8, 1–30 referred as I–II), we compute the contribution of unresolved mesoscale eddies to the large-scale dynamic equations of the ocean. In isopycnal coordinates, in addition to the bolus velocity discussed in I–II, the mesoscale contribution to the large scale momentum equation is derived. Its form is quite different from the traditional down-gradient parameterization. The model solutions in isopycnal coordinates are transformed to level coordinates to parameterize the eddy contributions to the corresponding large scale density and momentum equations. In the former, the contributions due to the eddy induced velocity and to the residual density flux across mean isopycnals (so called Σ-term) are derived, both contributions being shown to be of the same order. As for the large scale momentum equation, as well as in isopycnal coordinates, the eddy contribution has a form which is quite different from the down-gradient expression. 相似文献
45.
The effect of precipitation events on inorganic carbon in soil and shallow groundwater,Konza Prairie LTER Site,NE Kansas,USA 总被引:1,自引:0,他引:1
Monthly sampling for 1 year at the Konza Prairie LTER (Long-Term Ecological Research) Site in northeastern Kansas shows a connection between the annual cycles of CO2 in soil air and shallow groundwater DIC (dissolved inorganic C). Soil air CO2 reached 6–7% in July to mid-August, when moisture was not limiting to soil respiration. Following the annual maximum there was a sequential decrease in CO2 in three soil horizons to less than 0.5% because of moisture deficiency in the late summer and temperature decline in the fall and winter. Groundwater pCO2 reached its maximum of 5% in October; the lag-time of 2–3 months may correspond to the travel time of soil-generated CO2 to the water table. The time-variable CO2 caused an annual carbonate-mineral saturation cycle, intensifying limestone dissolution and DIC production when CO2 was high. 相似文献
46.
We review recent studies of the statistics of return intervals (i) in long-term correlated monofractal records and (ii) in
multifractal records in the absence (or presence) of linear long-term correlations. We show that for the monofractal records
which are long-term power-law correlated with exponent γ, the distribution density of the return intervals follows a stretched
exponential with the same exponent γ and the return intervals are long-term correlated, again with the same exponent γ. For
the multifractal record, significant differences in scaling behavior both in the distribuiton and correlation behavior of
return intervals between large events of different magnitudes are demonstrated. In the absence of linear long-term correlations,
the nonlinear correlations contribute strongly to the statistics of the return intervals such that the return intervals become
long-term correlated even though the original data are linearly uncorrelated (i.e., the autocorrelation function vanishes).
The distribution density of the return intervals is mainly described by a power law. 相似文献
47.
Maria V. Pastor Josep L. Pelegrí Alonso Hernández-Guerra Jordi Font Jordi Salat Mikhail Emelianov 《Continental Shelf Research》2008
A historical data set is used to describe the coastal transition zone off Northwest Africa during spring 1973 and fall 1975, from 17° to 26°N, with special emphasis on the interaction between subtropical (North Atlantic Central Waters) and tropical (South Atlantic Central Waters) gyres. The near-surface geostrophic circulation, relative to 300 m, is quite complex. Major features are a large cyclonic pattern north of Cape Blanc (21°N) and offshore flow at the Cape Verde front. The large cyclone occurs in the region of most intense winds, and resembles a large meander of the baroclinic southward upwelling jet. The Cape Verde frontal system displays substantial interleaving that may partly originate as mesoscale features at the coastal upwelling front. Property–property diagrams show that the front is an effective barrier to all properties except temperature. The analysis of the Turner angle suggests that the frontal system is characterized by large heat horizontal diffusion as a result of intense double diffusion, which results in the smoothing of the temperature horizontal gradients. Nine cross-shore sections are used to calculate along-shore geostrophic water-mass and nutrient transports and to infer exchanges between the coastal transition zone and the deep ocean (import: deep ocean to transition zone; export: transition zone to deep ocean). These exchanges compare well with mean wind-induced transports and actual geostrophic cross-shore transport estimates. The region is divided into three areas: southern (18–21°N), central (21–23.5°N), and northern (23.5–26°N). In the northern area geostrophic import is roughly compensated with wind-induced export during both seasons. In the central area geostrophic import is greater than wind-induced export during spring, resulting in net import of both water (0.8 Sv) and nitrate (14 kmol s−1), but during fall both factors again roughly cancel. In the southern area geostrophy and wind join to export water and nutrients during both seasons, they increase from 0.6 Sv and 3 kmol s−1 during fall to 2.9 Sv and 53 kmol s−1 during spring. 相似文献
48.
Alexei Pozdnoukhov Mikhail Kanevski 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(5):647-660
The algorithmic approach to data modelling has developed rapidly these last years, in particular methods based on data mining
and machine learning have been used in a growing number of applications. These methods follow a data-driven methodology, aiming
at providing the best possible generalization and predictive abilities instead of concentrating on the properties of the data
model. One of the most successful groups of such methods is known as Support Vector algorithms. Following the fruitful developments
in applying Support Vector algorithms to spatial data, this paper introduces a new extension of the traditional support vector
regression (SVR) algorithm. This extension allows for the simultaneous modelling of environmental data at several spatial
scales. The joint influence of environmental processes presenting different patterns at different scales is here learned automatically
from data, providing the optimum mixture of short and large-scale models. The method is adaptive to the spatial scale of the
data. With this advantage, it can provide efficient means to model local anomalies that may typically arise in situations
at an early phase of an environmental emergency. However, the proposed approach still requires some prior knowledge on the
possible existence of such short-scale patterns. This is a possible limitation of the method for its implementation in early
warning systems. The purpose of this paper is to present the multi-scale SVR model and to illustrate its use with an application
to the mapping of Cs137 activity given the measurements taken in the region of Briansk following the Chernobyl accident. 相似文献
49.
Volker Rachold Mikhail N. Grigoriev Felix E. Are Steve Solomon Erk Reimnitz Heidemarie Kassens Martin Antonow 《International Journal of Earth Sciences》2000,89(3):450-460
This article presents a comparison of sediment input by rivers and by coastal erosion into both the Laptev Sea and the Canadian Beaufort Sea (CBS). New data on coastal erosion in the Laptev Sea, which are based on field measurements and remote sensing information, and existing data on coastal erosion in the CBS as well as riverine sediment discharge into both the Laptev Sea and the CBS are included. Strong regional differences in the percentages of coastal erosion and riverine sediment supply are observed. The CBS is dominated by the riverine sediment discharge (64.45᎒6 t a-1) mainly of the Mackenzie River, which is the largest single source of sediments in the Arctic. Riverine sediment discharge into the Laptev Sea amounts to 24.10᎒6 t a-1, more than 70% of which are related to the Lena River. In comparison with the CBS, the Laptev Sea coast on average delivers approximately twice as much sediment mass per kilometer, a result of higher erosion rates due to higher cliffs and seasonal ice melting. In the Laptev Sea sediment input by coastal erosion (58.4᎒6 t a-1) is therefore more important than in the CBS and the ratio between riverine and coastal sediment input amounts to 0.4. Coastal erosion supplying 5.6᎒6 t a-1 is less significant for the sediment budget of the CBS where riverine sediment discharge exceeds coastal sediment input by a factor of ca. 10. 相似文献
50.
Bruno P. Besser Mikhail I. Pudovkin Valentina V. Lebedeva Svetlana A. Zaitseva Claudia-Veronika Meister 《Astrophysics and Space Science》2000,274(1-2):399-405
Variations of the magnetic field and plasma parameters across the Earth's magnetosheath are calculated for an anisotropic
plasma in the Chew-Goldberger-Low approximation. Additionally, proton pitch-angle diffusion is taken into account as the energy
transfer mechanism between the direction perpendicular and parallel to the magnetic field. We discuss the main characteristics
of the magnetic barrier for different temperature relaxation times and their dependence on the interplanetary magnetic field
orientation.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献