Compact non-singular expansions in the exterior space of a reference ellipsoid for the gravitational gradients in the local north-oriented ellipsoidal and spherical reference frames     

Margarita S. Petrovskaya  Andrey N. Vershkov 《Studia Geophysica et Geodaetica》2016,60(1):1-16

Due to the complicated structure of their expressions, the ellipsoidal harmonic series for the derivatives of the Earth’s gravitational potential are commonly applied only on a reference ellipsoid. They depend on the first- and second-order derivatives of the associated Legendre functions of both kinds and contain a few singular terms. We construct ellipsoidal harmonic expansions in the exterior space for the first and second potential derivatives, which are similar to the series on the reference ellipsoid enveloping the Earth. We take a point P at an arbitrary altitude above the reference ellipsoid and construct the ellipsoid of revolution confocal to it, which passes through this point. The conventional complicated singular expressions for the first and second potential derivatives in the local north-oriented ellipsoidal reference frame, with the origin at the point P, are transformed into non-singular ellipsoidal harmonic series, which do not contain the first- and second-order derivatives of the associated Legendre functions. The resulting series have an accuracy of the squared eccentricity. These series can be applied for constructing a geopotential model, which is based, simultaneously, on the surface gravity data and the data of satellite missions, which provide measurements of the accelerations and/or the gravitational gradients. When the eccentricity of the considered external ellipsoid is equated to zero, the ellipsoid becomes an external sphere passing through the point P and the constructed ellipsoidal harmonic expansions are converted into non-singular spherical harmonic series for the first and second potential derivatives in the local north-oriented spherical reference frame.  相似文献   

Long-term modification of Arctic lake ecosystems: Reference condition, degradation under toxic impacts and recovery (case study Imandra Lakes, Russia)     

Tatyana I. Moiseenko  Andrey N. Sharov  Lubov P. Kudryavtseva  Catherine Rose 《Limnologica》2009,39(1):1-13

In this study, published data on Lake Imandra, north-west Russia, have been synthesised to investigate trends in lake contamination and recovery due to changing inputs of heavy metals and nutrients over time. Records of water chemistry, phytoplankton, zooplankton and fish communities have been used to determine the status of aquatic ecosystem health in three distinct phases of Lake Imandra's recent history. Firstly, background (reference) conditions within the lake have been established to determine lake conditions prior to anthropogenic influences. Secondly, a period of ecosystem degradation due to anthropogenic inputs of toxic metals and nutrients has been described. Finally, evidence of lake recovery due to recent decreases of toxic metals and nutrients has been explored. Pollution of Lake Imandra began in the 1930s, reaching a peak in the 1980s. Increases in heavy metal and nutrient inputs transformed the typical Arctic ecosystem. During the contamination phase, there was a decrease in Arctic species and in biodiversity. During the last 10 years, pollution has decreased and the lake has been recolonised by Arctic water species. Ecosystem recovery is indicated by a change of predominant species, an increase in the individual mass of organisms and an increase in the biodiversity index of plankton communities. In accordance with Odum's ecosystem succession theory, this paper demonstrates that the ecosystem has transformed to a more stable condition with new defining parameters. This illustrates that the recovery of Arctic ecosystems towards pre-industrial reference conditions after a reduction in anthropogenic stresses occur, although a complete return to background conditions may not be achievable. Having determined the status of current ecosystem health within Lake Imandra, the effect of global warming on the recovery process is discussed. Climate warming in Arctic regions is likely to move the ecosystem towards a predominance of eurybiontic species in the community structure. These organisms have the ability to tolerate a wider range of environmental conditions than typical Arctic inhabitants and will gain advantages in development. This indicates that the full recovery of Arctic ecosystems in a warming climate may not be possible.  相似文献   

Modeling urban leaf area index with AISA+ hyperspectral data     

Ryan R. Jensen  Perry J. Hardin  Matthew Bekker  Derek S. Farnes  Vijay Lulla  Andrew Hardin 《Applied geography (Sevenoaks, England)》2009,29(3):320-332

This study used simple multiple regression to model urban leaf area index (LAI) in Terre Haute, Indiana, USA as a function of AISA+ hyperspectral radiance and its derivative features. Regression R² values ranging from 0.27 to 0.73 were obtained from the various models. Features appearing most frequently in the models included radiance at 0.727, 0.753, 0.848, 0.870, 0.900 and 0.917 μm. The best single predictor of LAI was the absolute difference in radiance between 0.777 and 0.673 μm. The best models performed well at low and intermediate LAI levels, but were less accurate with LAI values between 5.0 and 8.0.  相似文献   

Bed shear stress in the southern North Sea as an important driver for suspended sediment dynamics   总被引：3，自引：0，他引：3  

Emil Vassilev Stanev  Mikhail Dobrynin  Andrey Pleskachevsky  Sebastian Grayek  Heinz Günther 《Ocean Dynamics》2009,59(2):183-194

This paper addresses the spatial and temporal patterns of drivers for sediment dynamics in coastal areas. The basic assumption is that local processes are dominating. The focus is put on the bed shear stress in the southern part of North Sea giving the basic control for deposition–sedimentation and resuspension–erosion. The wave-induced bed shear stress is formulated using a model based on the concept that the turbulent kinetic energy associated with surface waves is a function of orbital velocity, the latter depending on the wave height and period, as well as on the water depth. Parameters of surface waves are taken from simulations with the wave spectrum model WAM (wave model). Bed shear stress associated with currents is simulated with a 3D primitive equation model, Hamburg Shelf Ocean Model. Significant wave height, bed shear stress due to waves and currents, is subjected to empirical orthogonal functions (EOF) analysis. It has been found that the EOF-1 of significant wave height represents the decrease of significant wave height over the shallows and, due to fetch limitation, along the coastlines. Higher order modes are seesaw-like and, in combination, display a basin-scale rotational pattern centred approximately in the middle of the basin. Similar types of variability is also observed in the second and third EOF of bed shear stress. Surface concentrations of suspended matter derived from MERIS satellite data are analysed and compared against statistical characteristics of bed shear stress. The results show convincingly that the horizontal distribution of sediment can, to a larger extent, be explained by the local shear stress. However, availability of resuspendable sediments on the bottom is quite important in some areas like the Dogger Bank.  相似文献   

The Air-Sea Exchange of CO2 in the East Sea (Japan Sea)     

Dong-Chan Oh  Mi-Kyung Park  Sang-Hwa Choi  Dong-Jin Kang  Sun Young Park  Jeom Shik Hwang  Andrey Andreev  Gi Hoon Hong  Kyung-Ryul Kim 《Journal of Oceanography》1999,55(2):157-169

During CREAMS expeditions, fCO₂ for surface waters was measured continuously along the cruise tracks. The fCO₂ in surface waters in summer varied in the range 320–440 μatm, showing moderate supersaturation with respect to atmospheric CO₂. In winter, however, fCO₂ showed under-saturation of CO₂ in most of the area, while varying in a much wider range from 180 to 520 μatm. Some very high fCO₂ values observed in the northern East Sea (Japan Sea) appeared to be associated with the intensive convection system developed in the area. A gas-exchange model was developed for describing the annual variation of fCO₂ and for estimating the annual flux of CO₂ at the air-sea interface. The model incorporated annual variations in SST, the thickness of the mixed layer, gas exchange associated with wind velocity, biological activity and atmospheric concentration of CO₂. The model shows that the East Sea releases CO₂ into the atmosphere from June to September, and absorbs CO₂ during the rest of the year, from October through May. The net annual CO₂ flux at the air-sea interface was estimated to be 0.032 (±0.012) Gt-C per year from the atmosphere into the East Sea. Water column chemistry shows penetration of CO₂ into the whole water column, supporting a short turnover time for deep waters in the East Sea. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

Climate states and variability of Arctic ice and water dynamics during 1946–1997     

Andrey Y. Proshutinsky  Igor V. Polyakov  Mark A. Johnson 《Polar research》1999,18(2):135-142

Recently observed changes in the Arctic have highlighted the need for a better understanding of Arctic dynamics. This research addresses that need and is also motivated by the recent finding of two regimes of Arctic ice - ocean wind-driven circulation. In this paper, we demonstrate that during 1946-1997 the Arctic environmental parameters have oscillated with a period of 10-15 years. Our results reveal significant differences among atmosphere, ice, and ocean processes during the anticyclonic and cyclonic regimes in the Arctic Ocean and its marginal seas. The oscillating behaviour of the Arctic Ocean we call the Arctic Ocean Oscillation (AOO). Based on existing data and results of numerical experiments, we conclude that during the anticyclonic circulation regime the prevailing processes lead to increases in atmospheric pressure, in ice concentration and ice thickness, river runoff, and surface water salinity - as well as to decreases in air temperature, wind speed, number of storms, precipitation, permafrost temperatures, coastal sea level, and surface water temperature. During the cyclonic circulation regime the prevailing processes lead to increased air and water temperatures, wind speed, number of storms,open water periods, and to decreases in ice thickness and ice concentration, river runoff, atmospheric pressure, and water salinity. The two-climate regime theory may help answer questions related to observed decadal variability of the Arctic Ocean and to reconcile the different conclusions among scientists who have analysed Arctic data obtained during different climate states.  相似文献   

Long-Term Global Warming Scenarios Computed with an Efficient Coupled Climate Model   总被引：13，自引：0，他引：13  

Stefan Rahmstorf  Andrey Ganopolski 《Climatic change》1999,43(2):353-367

We present global warming scenarios computed with an intermediate-complexity atmosphere-ocean-sea ice model which has been extensively validated for a range of past climates (e.g., the Last Glacial Maximum). Our simulations extend to the year 3000, beyond the expected peak of CO₂ concentrations. The thermohaline ocean circulation declines strongly in all our scenarios over the next 50 years due to a thermal effect. Changes in the hydrological cycle determine whether the circulation recovers or collapses in the long run. Both outcomes are possible within present uncertainty limits. In case of a collapse, a substantial long-lasting cooling over the North Atlantic and a drying of Europe is simulated.  相似文献   

Density profiles of dark matter haloes: diversity and dependence on environment     

Vladimir Avila-Reese  Claudio Firmani  Anatoly Klypin  Andrey V. Kravtsov 《Monthly notices of the Royal Astronomical Society》1999,310(2):527-539

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Development of Iron Speciation Reference Materials for Palaeoredox Analysis     

Lewis J. Alcott  Alexander J. Krause  Emma U. Hammarlund  Christian J. Bjerrum  Florian Scholz  Yijun Xiong  Andrew J. Hobson  Lesley Neve  Benjamin J. W. Mills  Christian Mrz  Bernhard Schnetger  Andrey Bekker  Simon W. Poulton 《Geostandards and Geoanalytical Research》2020,44(3):581-591

The development and application of geochemical techniques to identify redox conditions in modern and ancient aquatic environments has intensified over recent years. Iron (Fe) speciation has emerged as one of the most widely used procedures to distinguish different redox regimes in both the water column and sediments, and is the main technique used to identify oxic, ferruginous (anoxic, Fe(II) containing) and euxinic (anoxic, sulfidic) water column conditions. However, an international sediment reference material has never been developed. This has led to concern over the consistency of results published by the many laboratories that now utilise the technique. Here, we report an interlaboratory comparison of four Fe speciation reference materials for palaeoredox analysis, which span a range of compositions and reflect deposition under different redox conditions. We provide an update of extraction techniques used in Fe speciation and assess the effects of both test portion mass, and the use of different analytical procedures, on the quantification of different Fe fractions in sedimentary rocks. While atomic absorption spectroscopy and inductively coupled plasma‐optical emission spectrometry produced comparable Fe measurements for all extraction stages, the use of ferrozine consistently underestimated Fe in the extraction step targeting mixed ferrous–ferric minerals such as magnetite. We therefore suggest that the use of ferrozine is discontinued for this Fe pool. Finally, we report the combined data of four independent Fe speciation laboratories to characterise the Fe speciation composition of the reference materials. These reference materials are available to the community to provide an essential validation of in‐house Fe speciation measurements.  相似文献   

Dynamics of magnetic flux tubes and IR-variability of young stellar objects     

Sergey Khaibrakhmanov  Alexander Dudorov  Andrey Sobolev 《天文和天体物理学研究(英文版)》2018,(8)

We simulate the dynamics of slender magnetic flux tubes(MFTs) in the accretion disks of T Tauri stars. The dynamical equations of our model take into account aerodynamic and turbulent drag forces, and the radiative heat exchange between the MFT and ambient gas. The structure of the disk is calculated with the help of our MHD model of the accretion disks. We consider the MFTs formed at distances of 0.027-0.8 au from the star with various initial radii and plasma betas β_0. The simulations show that MFTs with a weak magnetic field(β_0= 10) rise slowly with speeds less than the speed of sound. MFTs with β_0= 1 form an outflowing magnetized corona above the disk. Strongly magnetized MFTs(β_0= 0.1) can cause outflows with velocities 20-50 km s~(-1). The tubes rise periodically over times from several days to several months according to our simulations. We propose that periodically rising MFTs can absorb stellar radiation and contribute to the IR-variability of young stellar objects.  相似文献