On the geodetic boundary value problem for a fixed boundary surface—A satellite approach     

Arne Bjerhammar  Leif Svensson 《Journal of Geodesy》1983,57(1-4):382-393

Employing satellite-geometrical methods, the physical surface of the earth may be assumed to be known, while gravity measurements yield thelength of the gravity vector (including contributions from rotation). The problem then is to determine gravitational potential from such gravity observations. The corresponding linearized problem is an oblique derivative problem. The problem was discussed by Almqvist (1959), Koch (1970, 1971) and Koch and Pope (1972). Our presentation gives proofs for the existence (and uniqueness) of the solution in the non-linear case. The general implicit function theorem (in Banach spaces) is used to provewellposedness at least when data are close to given standard values (closeness is defined either in terms of Hölder or Sobolev norms). Iterative methods for solution by linear operators are given. The linearized problem is solved by harmonic reduction to an internal sphere in a generalization of the method by the first author for the Stokes problem. Also deflections of the vertical are treated.  相似文献   

Solution of the altimetry-gravimetry problem     

S. Leif Svensson 《Journal of Geodesy》1983,57(1-4):332-353

Unique solvability of the altimetry-gravimetry problem is proved for general ocean configurations and for models which are close to the classical Stokes model provided that a zero-degree component is removed from both gravity anomaly and disturbed potential. Data and solutions are to belong to suitable Sobolev spaces. The theory of pseudodifferential operators plays an important part in the proof. Finite element methods for numerical computations are suggested and convergence rates are estimated. Holota (1980, 1981a, b, 1982) has proved wellposedness of the problem without constraints for small continents by variational methods. The present paper yields wellposedness without any constraints when the diameter of the continental area is smaller than 62°.6. There are strong indications, very disturbing considering the amount of work spent on the method for the last two decades, that the direct least squares approach is unstable for mixed sets of data.  相似文献   

ON THE SENSITIVITY OF PRECIPITATION FORECASTS TO THE MOIST PHYSICS AND THE HORIZONTAL RESOLUTION OF NUMERICAL MODEL     

俞小鼎  Leif Laursen  Erik Rasmussen 《Acta Meteorologica Sinica》1997,(4)

The impacts of the enhanced model's moist physics and horizontal resolution upon the QPFs(quantitative precipitation forecasts)are investigated by applying the HIRLAM(high resolutionlimited area model)to the summer heavy-rain cases in China.The performance of the control run,for which a 0.5°×0.5°grid spacing and a traditional“grid-box supersaturation removal+Kuo typeconvective paramerization”are used as the moist physics,is compared with that of the sensitivityruns with an enhanced model's moist physics(Sundqvist scheme)and an increased horizontalresolution(0.25°×0.25°),respectively.The results show:(1)The enhanced moist physics scheme(Sundqvist scheme),by introducing the cloud watercontent as an additional prognostic variable and taking into account briefly of the microphysicsinvolved in the cloud-rain conversion,does bring improvements in the model's QPFs.Althoughthe deteriorated QPFs also occur occasionally,the improvements are found in the majority of thecases,indicating the great potential for the improvement of QPFs by enhancing the model's moistphysics.(2)By increasing the model's horizontal resolution from 0.5°×0.5°,which is already quitehigh compared with that of the conventional atmospheric soundings,to 0.25°×0.25°without thesimultaneous enhancement in model physics and objective analysis,the improvements in QPFs arevery limited.With higher resolution,although slight amelioration in locating the rainfall centersand in resolving some finer structures of precipitation pattern are made,the number of the mis-predicted fine structures in rainfall field increases with the enhanced model resolution as well.  相似文献   

A study of wind speed modification and internal boundary-layer heights in a coastal region     

Hans Bergström  Per-Erik Johansson  Ann-Sofi Smedman 《Boundary-Layer Meteorology》1988,42(4):313-335

Wind profile data within the first two kilometres of a coast have been used to study the wind field modification downstream of this surface discontinuity. The land area is generally very flat, having an overall roughness length of 0.04 m. A wind model, suitable for practical applications and inexpensive to run, has been tested against the data and was found to give satisfactory results. Knowing the climatological statistics of wind and stratification, e.g., at the coast, the model may thus be used to estimate, on a climatological basis, how the wind field is modified with distance inland, at least in areas with only minor topography. This type of information is of great importance when locating wind turbines. It is in these cases also important to know the statistics of the internal boundary-layer (IBL) height, as the turbulence intensity may be quite different in and above the IBL, which in turn may influence load and fatigue calculations. Using the wind profile data, the IBL height was clearly discernible in the majority of cases. Having very unstable stratification over land, the IBL height could, however, not be determined from the wind profiles, as the wind in these cases did not decrease inland. This result was also obtained using the wind model. A simple model of the type z _IBL = a · x ^b, was instead tested, and was shown to give reasonable results.  相似文献   

Estimation of groundwater recharge in sandy till with two different methods using groundwater level fluctuations     

Per-Olof Johansson 《Journal of Hydrology》1987,90(3-4):183-198

Two methods for estimation of groundwater recharge, both based on groundwater level fluctuations, were applied in a moraine area in southeastern Sweden. The first method utilized a onedimensional soil water model which was tested against observed groundwater levels. The boundary conditions were defined by using standard meteorological data and submodels for precipitation, snow dynamics, interception, evapotranspiration and horizontal groundwater outflow. The second method directly transformed groundwater level fluctuations to equivalent amounts of water from a constructed recession curve and the specific yield concept. Conceptually the two methods could be characterized as inflow and response methods respectively.

A good fit between observed and simulated groundwater levels was obtained by the soil water modelling. The results were, however, shown to be rather insensitive to displacement in the water balance between evapotranspiration and groundwater outflow, giving a good fit for a simulated net groundwater recharge ranging between 134 and 197 mm. The results from the attempts to use groundwater level fluctuations directly were discouraging. Compared to the soil water simulations the results were unstable and quite different for different years. It was impossible to use a constant specific yield or even different specific yields depending on depth.

The conclusion was that the possibilities to use groundwater level data for quantitative water balance studies are limited under the studied climatical and hydrogeological conditions. The modelling effort clearly demonstrated the need for a better quantitative knowledge on soil properties if water balance information is to be deduced. The soil water model though, could be a valuable tool studying variations within and between different years as well as processes and single events.  相似文献   

Sediment pollution in the Vågen,Bergen harbour,Norway     

Matthias Paetzel  Geir Nes  Leif Leifsen  Hans Schrader 《Environmental Geology》2003,43(4):476-483

Recent sediments in the Vågen, Bergen harbour, are subjected to injection of untreated sewage from around 15,000 person equivalent. Here the distribution of trace elements is mapped in surface and subsurface sediments. Selected trace-element concentrations decrease from the inner towards the outer Vågen. These concentration gradients do not correlate with minerogenic grain size. Linear correlation, combined with enriched sediment trace elements, are used to infer sources for these elements and possible reasons for their enrichment. (1) Frequent use of dental amalgam might be related to the enrichments of and correlation between Ag, Cu, Hg and Sn in surficial sediments pre-1994. (2) Enrichment and correlation of Cu/Zn may be related to the commercial and private use of anti-fouling boat-paint. Further, tributyltin is suggested as a source of Sn enrichment. (3) Increased traffic in the city of Bergen with gasoline combustion and car-wheel wear-off release Pb and Zn. (4) Hg and Pb might have been atmospherically supplied due to the combustion of coal in a nearby gas plant pre-1985. (5) No correlation is observed between enriched Vågen trace metals and bedrock element composition of the surrounding mountains, indicating a minor supply from erosion.  相似文献   

Astrophysical laser operating in the O i 8446-Å line in the Weigelt blobs of η Carinae     

S. Johansson  V. S. Letokhov 《Monthly notices of the Royal Astronomical Society》2005,364(2):731-737

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Sources to the East Greenland Current and its contribution to the Denmark Strait Overflow     

Emil Jeansson  Sara Jutterström  Leif G. Anderson  E. Peter Jones  James H. Swift 《Progress in Oceanography》2008,78(1):12-28

Data from the East Greenland Current in 2002 are evaluated using optimum multiparameter analysis. The current is followed from north of Fram Strait to the Denmark Strait Sill and the contributions of different source waters, in mass fractions, are deduced. From the results it can be concluded that, at least in spring 2002, the East Greenland Current was the main source for the waters found at the Denmark Strait Sill, contributing to the overflow into the North Atlantic. The East Greenland Current carried water masses from different source regions in the Arctic Ocean, the West Spitsbergen Current and the Greenland Sea. The results agree well with the known circulation of the western Nordic Seas but also add knowledge both to the quantification and to the mixing processes, showing the importance of the locally formed Greenland Sea Arctic Intermediate Water for the East Greenland Current and the Denmark Strait.  相似文献   

Constraints on incipient charnockite formation from zircon geochronology and rare earth element characteristics     

A. Rimša  L. Johansson  M. J. Whitehouse 《Contributions to Mineralogy and Petrology》2007,154(3):357-369

We present high spatial resolution ion-microprobe U–Th–Pb geochronology and rare earth element (REE) data combined with cathodoluminescence (CL) and back-scattered electron (BSE) imaging for complex zircons in incipient charnockites from Söndrum, SW Sweden. Examination of closely paired samples across the dehydration zone demonstrates that incipient charnockite formation at Söndrum is a zircon-forming process. We determined the age of the dehydration event (i.e. charnockitisation) to 1,397 ± 4 Ma (2σ, MSWD = 1.7). This is the first successful attempt to date incipient charnockite formation using U–Pb systematics of zircon. Internal structure, chemical and isotopic characteristics of zircon indicate that the granitic pegmatite in the core of the incipient charnockite is a melting zone. Commonly observed bulk rock HREE depletion in incipient charnockites is not caused by zircon dissolution but by involvement of garnet as a reactant in the dehydration reactions. Moreover, REE patterns of the newly formed zircon are HREE-enriched, indicating non-concurrent growth and suggesting that the degree of charnockite depletion in HREE might be controlled by the volume of newly formed zircon.  相似文献   

A scenario based analysis of land competition between food and bioenergy production in the US     

Daniel J. A. Johansson  Christian Azar 《Climatic change》2007,82(3-4):267-291

Greenhouse gas abatement policies will increase the demand for renewable sources of energy, including bioenergy. In combination with a global growing demand for food, this could lead to a food-fuel competition for bio-productive land. Proponents of bioenergy have suggested that energy crop plantations may be established on less productive land as a way of avoiding this potential food-fuel competition. However, many of these suggestions have been made without any underlying economic analysis. In this paper, we develop a long-term economic optimization model (LUCEA) of the U.S. agricultural and energy system to analyze this possible competition for land and to examine the link between carbon prices, the energy system dynamics and the effect of the land competition on food prices. Our results indicate that bioenergy plantations will be competitive on cropland already at carbon taxes about US $20/ton C. As the carbon tax increases, food prices more than double compared to the reference scenario in which there is no climate policy. Further, bioenergy plantations appropriate significant areas of both cropland and grazing land. In model runs where we have limited the amount of grazing land that can be used for bioenergy to what many analysts consider the upper limit, most of the bioenergy plantations are established on cropland. Under the assumption that more grazing land can be used, large areas of bioenergy plantations are established on grazing land, despite the fact that yields are assumed to be much lower (less than half) than on crop land. It should be noted that this allocation on grazing land takes place as a result of a competition between food and bioenergy production and not because of lack of it. The estimated increase in food prices is largely unaffected by how much grazing land can be used for bioenergy production.  相似文献