The acoustic target strength of herring (Clupea harengus L.) in the northern Baltic Sea   总被引：1，自引：0，他引：1  

Peltonen  Heikki; Balk  Helge 《ICES Journal of Marine Science》2005,62(4):803-808

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Multi-species chemical data assimilation with the Danish Eulerian hemispheric model: system description and verification     

Jeremy D. Silver  Jesper H. Christensen  Michael Kahnert  Lennart Robertson  Peter J. Rayner  Jørgen Brandt 《Journal of Atmospheric Chemistry》2016,73(3):261-302

Satellite retrievals of atmospheric composition provide a wealth of data on a global scale. These complement results from atmospheric chemistry-transport models (CTMs), and can be combined using data assimilation. We present two assimilation schemes coupled to the Danish Eulerian Hemispheric Model (DEHM), a three-dimensional, off-line CTM with full photochemistry: a variant on the ensemble Kalman filter and the three-dimensional variational scheme. The aim of this paper is to describe the two schemes and present an initial assessment of their impacts on model skill. Retrievals of multiple atmospheric trace gases are assimilated, namely: NO₂ tropospheric column densities, CH₄ total column densities, and partial column concentrations of O₃, CO and CH₄; these data are retrieved from four satellite sensors. Data for each species are assimilated independently of one another, and other species are only adjusted indirectly via the model’s chemistry and dynamics. Assimilation results are compared with measurements from surface monitoring stations and other satellite retrievals, and preliminary validation results are presented.Reference simulations (without assimilation) grossly underestimate surface CO concentrations, and both assimilation schemes eliminate this large and systematic model bias. The assimilation improves the spatial correlation of modelled CO with surface observations, and improves the spatial correlation between forecasts and retrievals for CO, NO₂ and O₃. Results for CH₄ show a loss of skill due to a mismatch in model bias between two assimilated CH₄ data-sets. Finally, we discuss differences in methodology and results between this paper and a recent study on multi-species chemical data assimilation. Joint optimisation of initial conditions and emission rates offers a promising direction for improving modelled boundary-layer concentrations.  相似文献   

Desertification in Africa — A critique and an alternative approach     

Lennart Olsson 《GeoJournal》1993,31(1):23-31

This article critically reviews the international debate on desertification, its status and rate as well as causes and consequences. The article rejects the commonly used concept of a degrading environment, but tries to explain the environmental problems as symptoms of a wider economic and political crisis. An alternative approach applying systems analysis of the entire socio-economic-system to the study of desertification and land degradation is discussed, with examples from the Western Sudan.  相似文献   

Water flow and swelling pressure in non-saturated bentonite-based clay barriers     

Lennart Brgesson 《Engineering Geology》1985,21(3-4):229-237

The water uptake of 10 and 20% bentonite—sand mixtures and of 100% pure bentonite was studied experimentally. The results were compared with calculated water content distributions to study the usefulness of the diffusion equation. The relation between the swelling pressure and the degree of saturation of a bentonite was also studied.  相似文献   

Experimental evidence for an ascending microflow of geogas in the ground   总被引：2，自引：0，他引：2  

Lennart Malmqvist  Krister Kristiansson 《Earth and Planetary Science Letters》1984,70(2):407-416

A microflow of free ascending gas has been observed in 26 out of 30 tested boreholes at three different sites. The flow rates vary between 60 × 10⁻⁴ and 4 cm³/min m² horizontally projected borehole area. Sampling has been made in ground boreholes as well as in holes drilled downwards from the lowest levels in two mines. The composition of the gas varies considerably. The main components of the gas are nitrogen, argon, oxygen and methane. Traces of heavier hydrocarbons are observed. At the site of the ground holes, only traces of methane are observed. In all sampled holes the existence of free oxygen is observed. The nitrogen/argon quotient is close to the atmospheric quotient in all sampled holes, indicating a partly atmospheric origin of the gas. The existence of methane and traces of heavier hydrocarbons indicates the existence of a second source.  相似文献   

Temperature dependence of calcite dissolution kinetics between 1 and 62°C at pH 2.7 to 8.4 in aqueous solutions   总被引：1，自引：0，他引：1  

E.Lennart Sjöberg  David T. Rickard 《Geochimica et cosmochimica acta》1984,48(3):485-493

The kinetics of calcite dissolution in aqueous KCl-solutions far from equilibrium, between 1 and 62°C in the pH-range 2.7 to 8.4 have been investigated using a rotating disc apparatus. At neutral and alkaline pH in the mixed kinetic regime the empirical apparent activation energy (EAAE) for the surface chemical reaction rate constant is 54 ± 4 kJ mole^?1 for Carrara marble and 46 ± 4 kJ mole^?1 for Iceland spar. Under similar conditions the EAAE of the transport rate constant increases with decreasing temperature, but has a mean value of 27 ± 2 kJ mole^?1. The corresponding diffusion coefficient has a mean EAAE of 37 ± 3 kJ mole^?1 and this high EAAE is consistent with transport dependence on product diffusion in this H⁺-independent regime.In contrast, in acid solutions, where the rate approaches end-member transport control, the EAAE of the diffusion coefficient is 16 kJ mole^?1, also decreasing with increasing temperature. This is compatible with H⁺-diffusion to the surface being rate-controlling.In inhibitor-free natural systems, calcite dissolution kinetics far from equilibrium can be described in terms of three regimes: an H⁺-dependent regime (pH < 4 at 25°C), a transition regime (4 < pH < 5.5 at 25°C) and an H⁺-independent regime (pH > 5.5 at 25°C). At lower temperatures these boundaries move to higher pH values. The presence of inhibitors in natural systems may enhance surface controlled kinetics.  相似文献   

Strain parameters of discontinuities in rock for finite element calculation   总被引：1，自引：0，他引：1  

Roland Pusch  Lennart Brgesson 《Engineering Geology》1998,49(3-4):201-206

The bulk strain induced by excavation of rooms for storage of highly radioactive waste is usually unimportant, but the change in aperture and shear displacement of permeable fractures may be of practical importance. Hence, the normal and shear of such discontinuities have to be considered and are commonly predicted by using special deformation moduli termed “normal” and “shear” stiffnesses in numerical calculations. For the use of some finite element methods, these have to be converted to compression and shear moduli ,which, in turn, requires that the thickness of the discontinuity is known. The normal and shear strain can be expressed in terms of soil mechanical parameters, yielding the compression modulus M and the shear modulus G, with the required form for finite element calculations. By definition they are functions of the normal and shear stiffness K_n and K_s. It is concluded that calculation of the normal and shear strain of discontinuities with clastic fillings by the use of finite element methods and deformation moduli derived from stiffness numbers is very uncertain except when the geometry of the weaknesses can be accurately defined.  相似文献   

Remotely sensed assessment of water quality levels in the Pearl River Estuary, China   总被引：3，自引：0，他引：3  

Chen C  Tang S  Pan Z  Zhan H  Larson M  Jönsson L 《Marine pollution bulletin》2007,54(8):1267-1272

In this paper, a method of assessing water quality from satellite data is introduced. The composite pollution index (CPI) was calculated from measured chemical oxygen demand (COD) and nutrient concentration. The relationships between CPI and 240 band combinations of SeaWiFS water-leaving radiance were analyzed and the optimal band combination for estimating CPI was chosen from the 240 band combinations. An algorithm for retrieval of CPI was developed using the optimal band combination, (L₄₄₃ × L₅₁₀)/(L₄₁₂ + L₄₉₀). The CPI was estimated from atmospherically corrected SeaWiFS data by employing the algorithm. Furthermore, the CPI value range for each water quality level was determined based on data obtained from 850 samples taken in the Pearl River Estuary. The remotely sensed CPIs were then transferred to water quality levels and appropriate maps were derived. The remotely sensed water quality level maps displayed a similar distribution of levels based on in situ investigation issued by the State Ocean Administration, China. This study demonstrates that remote sensing can play an important role in water quality assessment.  相似文献   

Deterministic approach to the problem of reliability in interpretation results of gravimetric data     

P. I. Balk  A. S. Dolgal 《Doklady Earth Sciences》2010,431(1):334-338

A method for comparative estimation of reliability in detection of gravity anomaly sources in indicated fragments of studied geological space is given. The possibility of creation of this estimation is connected with disparate ideas on different peculiarities of the structure of studied geological space and noise characteristics in observed fields. The model example and results of practical problem solution are viewed.  相似文献   

Synthesis of feasible solutions of the inverse problem to prepare recommendations for the verification of gravity anomalies     

P. I. Balk  A. S. Dolgal 《Doklady Earth Sciences》2014,458(2):1236-1240

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