The diffuse interstellar band carriers in interstellar space: all intense bands calculated from He doubly excited states embedded in Rydberg Matter     

Leif Holmlid 《Monthly notices of the Royal Astronomical Society》2008,384(2):764-774

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A Simple Model for the Vertical Transport of Reactive Species in the Convective Atmospheric Boundary Layer     

Leif Kristensen  Donald H. Lenschow  David Gurarie  Niels Otto Jensen 《Boundary-Layer Meteorology》2010,134(2):195-221

We have developed a simple, steady-state, one-dimensional second-order closure model to obtain continuous profiles of turbulent fluxes and mean concentrations of non-conserved scalars in a convective boundary layer without shear. As a basic tool we first set up a model for conserved species with standard parameterizations. This leads to formulations for profiles of the turbulent diffusivity and the ratio of temperature-scalar covariance to the flux of the passive scalar. The model is then extended to solving, in terms of profiles of mean concentrations and fluxes, the NO _x –O₃ triad problem. The chemical reactions involve one first-order reaction, the destruction of NO₂ with decay time τ, and one second-order reaction, the destruction of NO and O₃ with the reaction constant k. Since the fluxes of the sum concentrations of NO _x = NO + NO₂ and O₃ + NO₂ turn out to be constant throughout the boundary layer, the problem reduces to solving two differential equations for the concentration and the flux of NO₂. The boundary conditions are the three surface fluxes and the fluxes at the top of the boundary layer, the last obtained from the entrainment velocity, and the concentration differences between the free troposphere and the top of the boundary layer. The equations are solved in a dimensionless form by using 1/(kτ) as the concentration unit, the depth h of the boundary layer as the length unit, the convective velocity scale w _* as the velocity unit, and the surface temperature flux divided by w _* as the temperature unit. Special care has been devoted to the inclusion of the scalar–scalar covariance between the concentrations of O₃ and NO. Sample calculations show that the fluxes of the reactive species deviate significantly from those of non-reactive species. Further, the diffusivities, defined by minus the flux divided by the concentration gradient may become negative for reactive species in contrast to those of non-reactive species, which in the present model are never negative.  相似文献   

Fluxes and Concentrations of Non-Conserved Scalars in the Atmospheric Surface Layer     

Leif Kristensen  Peter Kirkegaard 《Journal of Atmospheric Chemistry》2006,53(3):251-263

We have carried out a theoretical study of the simplest possible, second-order, chemical destruction process in the atmospheric surface layer. The model describes the destruction of two gases emanating from the surface with the same molecular flux. Although this situation seems artificial with no counterpart in the real atmosphere, the results shed light on some fundamental problems. For example, it is possible to specify boundary conditions, with the concentrations and the fluxes at a given height away from the surface, which lead to unrealistic solutions with infinite surface fluxes. A method to describe and separate the consistent solutions for this process was developed. It is in general of particular interest from an experimental point of view since it is not possible to measure fluxes right at the surface: if a measurement of flux and concentration in a given height requires infinite surface fluxes there is something wrong with the data. We expect that such problems will be inherent in more complex reactions schemes, such as the NO-NO₂-O₃ triad. Just as in first-order destruction processes, the Damköhler ratio will enter the turbulent diffusivity, but where this ratio is concentration independent for first-order processes, the present second-order model implies that the Damköhler ratio is proportional to the concentration. In the study of first-order processes it was found that the Damköhler correction to the turbulent diffusivity is of minor importance from an experimental point of view. We arrive at the same conclusion in this particularly simple study of second-order destruction. In other words, this work may be considered a further development of a previous study of the first-order destruction of a passive scalar. The model and the method we develop to solve the corresponding nonlinear differential equations are considered a preliminary study for developing tools to deal with more complicated atmospheric processes. Also, the results obtained may serve as a “calibration case” for more elaborate simulations.  相似文献   

The effect of copper-treated net pens on farmed salmon (Salmo salar) and other marine organisms and sediments     

Solberg CB  Saethre L  Julshamn K 《Marine pollution bulletin》2002,45(1-12):126-132

Samples of Atlantic salmon (Salmo salar), saithe (Pollacius virens), blue mussel (Mytilus edulis), brown seaweed (Ascophyllum nodosum) and sediment were collected from six different fish farms. Five of the farms used net pens treated with copper-containing coatings, whereas one farm did not use copper-containing coating (this was used as a reference location). Samples of muscle, liver and gills of Atlantic salmon and saithe, blue mussel and brown seaweed were freeze dried, homogenised, wet digested and analysed for copper by flame atomic absorption spectrometry. The results showed no significant differences in copper concentrations among the samples from the different locations. The copper contents of some of the samples appeared to be in the upper part of the normal concentration range. From a nutritional point of view, the use of copper-coatings on net pens did not affect the quality of the seafood products either within, or around the net pen.  相似文献   

Petrogenesis of ultramafic and mafic xenoliths from Mesozoic basanites in southern Sweden: constraints from mineral chemistry     

Tatjana Rehfeldt  Karsten Obst  Leif Johansson 《International Journal of Earth Sciences》2007,96(3):433-450

Jurassic basanite necks occurring at the junction of two major fault zones in Scania contain ultramafic (peridotites, pyroxenites) and mafic xenoliths, which together indicate a diversity of upper mantle and lower crustal assemblages beneath this region. The peridotites can be subdivided into lherzolites, dunites and harzburgites. Most lherzolites are porphyroclastic, containing orthopyroxene and olivine porphyroclasts. They consist of Mg-rich silicates (Mg# = Mg/(Mg + Fe_tot) × 100; 88–94) and vermicular spinel. Calculated equilibration temperatures are lower in porphyroclastic lherzolites (975–1,007°C) than in equigranular lherzolite (1,079°C), indicating an origin from different parts of the upper mantle. According to the spinel composition the lherzolites represent residues of 8–13% fractional melting. They are similar in texture, mineralogy and major element composition to mantle xenoliths from Cenozoic Central European volcanic fields. Dunitic and harzburgitic peridotites are equigranular and only slightly deformed. Silicate minerals have lower to similar Mg# (83–92) as lherzolites and lack primary spinel. Resorbed patches in dunite and harzburgite xenoliths might be the remnants of metasomatic processes that changed the upper mantle composition. Pyroxenites are coarse, undeformed and have silicate minerals with partly lower Mg# than peridotites (70–91). Pyroxenitic oxides are pleonaste spinels. According to two-pyroxene thermometry pyroxenites show a large range of equilibration temperatures (919–1,280°C). In contrast, mafic xenoliths, which are mostly layered gabbronorites with pyroxene- and plagioclase-rich layers, have a narrow range of equilibration temperatures (828–890°C). These temperature ranges, together with geochemical evidence, indicate that pyroxenites and gabbroic xenoliths represent mafic intrusions within the Fennoscandian crust.  相似文献   

Radiocarbon dating of subfossil Scots pine (Pinus sylvestris L.) in the southern Swedish Scandes     

Leif Kullman 《Boreas: An International Journal of Quaternary Research》1980,9(2):101-106

Wood samples from above the present-day pine limit were collected from within a limited area in central Sweden. New dates from an intensively investigated part of that area all fall within the period 8550 ± 110 to 4270 ± 90 ¹⁴C years B. P. No evidence at present exists to suggest that any drastic change, or fluctuations, in the pine tree-limit, took place within that period. Some dates support the view that the present-day altitude of the pine tree-limit was established during the historic period and perhaps is still declining.  相似文献   

The 1859 Solar–Terrestrial Disturbance And the Current Limits of Extreme Space Weather Activity     

E. W. Cliver  L. Svalgaard 《Solar physics》2004,224(1-2):407-422

It is generally appreciated that the September 1859 solar–terrestrial disturbance, the first recognized space weather event, was exceptionally large. How large and how exceptional? To answer these questions, we compiled rank order lists of the various measures of solar-induced disturbance for events from 1859 to the present. The parameters considered included: magnetic crochet amplitude, solar energetic proton fluence (McCracken et al., 2001a), Sun–Earth disturbance transit time, geomagnetic storm intensity, and low-latitude auroral extent. While the 1859 event has close rivals or superiors in each of the above categories of space weather activity, it is the only documented event of the last ～150 years that appears at or near the top of all of the lists. Taken together, the top-ranking events in each of the disturbance categories comprise a set of benchmarks for extreme space weather activity.  相似文献   

Carbon fluxes in the Arctic Ocean—potential impact by climate change   总被引：1，自引：0，他引：1  

Leif G. Anderson  Staffan Kaltin 《Polar research》2001,20(2):225-232

Because of its ice cover the central Arctic Ocean has not been considered as a sink of atmospheric carbon dioxide. With recent observations of decreasing ice cover there is the potential for an increased air–sea carbon dioxide flux. Though the sensitivity of the carbon fluxes to a climate change can at present only be speculated, we know the responses to some of the forcing, including: melting of the sea ice cover make the air–sea flux operate towards equilibrium; increased temperature of the surface water will decrease the solubility and thus the air-sea flux; and an open ocean might increase primary production through better utilization of the nutrients.
The potential change in air-sea CO₂ fluxes caused by different forcing as a result of climate change is quantified based on measured data. If the sea ice melts, the top 100 m water column of the Eurasian Basin has, with the present conditions, a potential to take up close to 50 g C m⁻². The freshening of the surface water caused by a sea ice melt will increase the CO₂ solubility corresponding to an uptake of ∼ g C m⁻², while a temperature increase of 1°C in the same waters will out-gas 8 g C m⁻², and a utilization of all phosphate will increase primary production by 75 g C m⁻².  相似文献   

Geochemistry of Caledonian metabasalts from some Norwegian ophiolite fragments     

Harald Furnes  Asbjørn Thon  Jan Nordås  Leif B. Garmann 《Contributions to Mineralogy and Petrology》1982,79(3):295-307

Major and trace element analyses of metabasalts from five of the Lower Palaeozoic Caledonian ophiolite fragments along a strike distance of some 800 km of the west Norwegian coast are presented. Characteristically the REE patterns show depletion of both LREE and HREE relative to intermediate REE, giving an upward convex shape, but nearly flat, LREE depleted or enriched patterns occur. The REE patterns of the metabasalts from three of these sequences, i.e. the Lykling, Solund and Stavfjorden ophiolite fragments show little within-sequence but large between-sequence variation. The REE patterns of the metabasalts from the Gullfjellet (Major Bergen Arc) and Skålvær ophiolite fragments, however, show significant within-sequence variations, indicative of local source heterogeneties.When incompatible trace elements such as Ta, Nb, Ce, P, Zr, Hf, Sm, Ti, Y and Yb are normalized against average MORB, the metabasalts can be subdivided into two major groups. One group, geographically comprising the ophiolite fragments north of Bergen (i.e. Solund, Stavfjorden og Skålvær) show trace element ratios similar to average MORB, whereas the other group, defined by the Gullfjellet and Lykling ophiolite fragments (from Bergen southwards) differ significantly with respect to Yb/Y, Ti/Y and Nb/Ce ratios. These features are discussed in terms of trace element patterns in basalts from oceanic islands, island arcs and back-arc basins, and it is tentatively concluded that they reflect partial melts from a mid-oceanic mantle, or probably a back-arc basin mantle, which differed chemically from that of the northwestern Norwegian ophiolite fragments.  相似文献   

A Younger Dryas Ash Bed in western Norway,and its possible correlations with tephra in cores from the Norwegian Sea and the North Atlantic     

Jan Mangerud  Sven Erik Lie  Harald Furnes  Inger Lise Kristiansen  Leif Lømo 《Quaternary Research》1984,21(1):85-104

A bed of volcanic ash up to 23 cm thick is found in lacustrine and marine sediments in western Norway. It is formally mamed the Vedde Ash Bed, and its age is approximately 10,600 yr B.P., i.e., mid-Younger Dryas. The bed consits of pure glass having a bimodal basaltic and rhyolitic somposition. The geochemistry of the glass shards suggests an Icelandic source. By means of stratigraphic position and geochemistry, the ash is correlated with ash zones found in cores from the continental shelf, the Norwegian Sea, and the North Atlatic.  相似文献