Summertime diurnal variations of atmospheric peroxides and formaldehyde in Sweden     

Howard B. Ross  Christer Johansson  Claes de Serves  John Lind 《Journal of Atmospheric Chemistry》1992,14(1-4):411-423

Atmospheric peroxides and formaldehyde were measured at two sites in Sweden; inside a Scots pine stand (Jädraås) and on top of Mt. Åreskutan (1250 msl). Peroxide levels at Jädraås were highest during the day and lowest during the night. Mid-day concentrations of H₂O₂ varied between 0.05 and 2 ppbv. Isentropic trajectories together with local O₃ measurements indicated the importance of long range transport on surface H₂O₂ lévels. Large diurnal variations and vertical profiles showed the importance of turbulent mixing processes and dry deposition. A comparison of H₂O₂ and O₃ diurnal variations indicated a more rapid dry deposition of H₂O₂ to the forest. It would appear that terpenes emitted from the forest play a minor role in controlling the H₂O₂ levels. Formaldehyde at Jädraås had a different diurnal variation than peroxides; highest levels were observed in the early evening indicating chemical production of CH₂O. Diurnal variations of peroxides on Mt Åreskutan were opposite to those at Jädraås, highest concentrations were observed during the night. This result is to be expected if during the day air from inside the valley, with lower peroxide levels relative to the free troposphere, rises to the mountain top. In the evening, subsidence brings free tropospheric air with higher peroxides levels to the mountain.  相似文献   

On the use of the autocorrelation method for estimating the depth to the magnetic basement     

Jan Reidar Skilbrei  Ola Kihle 《Pure and Applied Geophysics》1992,138(3):501-506

The depth to the top of magnetic dykes can be estimated from total field aeromagnetic data using the relation between the depth to magnetic sources and the autocorrelation function of magnetic data. By using synthetic anomalies we show that in the ideal case, depth can be determined to an accuracy of 10% or better, when the anomaly sources are two-dimensional dykes. However, the estimated depths depend on the width of the dykes. The estimated depth is about 0.6 times the actual depth to the top of thin dykes, and around the true depth for thick dykes having width-to-depth ratio around 3. The depth is considerably overestimated for very thick dykes (e.g., contacts, which is a special case of the thick dyke). Thus, the autocorrelation method requires that the width-to-depth ratio of the dyke is estimated independently to correctly estimate the depths. Alternatively, it must be assumed that the width-to-depth ratio for the two-dimensional source body is between 1.5 and 4.  相似文献   

Estimation of winter leaf area index and sky view fraction for snow modelling in boreal coniferous forests: consequences on snow mass and energy balance     

Sirpa Rasmus  David Gustafsson  Harri Koivusalo  Ari Laurén  Achim Grelle  Olli‐Kalle Kauppinen  Ola Lagnvall  Anders Lindroth  Kai Rasmus  Magnus Svensson  Per Weslien 《水文研究》2013,27(20):2876-2891

Leaf area index (LAI) and canopy coverage are important parameters when modelling snow process in coniferous forests, controlling interception and transmitting radiation. Estimates of LAI and sky view factor show large variability depending on the estimation method used, and it is not clear how this is reflected in the calculated snow processes beneath the canopy. In this study, the winter LAI and sky view fraction were estimated using different optical and biomass‐based approximations in several boreal coniferous forest stands in Fennoscandia with different stand density, age and site latitude. The biomass‐based estimate of LAI derived from forest inventory data was close to the values derived from the optical measurements at most sites, suggesting that forest inventory data can be used as input to snow hydrological modelling. Heterogeneity of tree species and site fertility, as well as edge effects between different forest compartments, caused differences in the LAI estimates at some sites. A snow energy and mass balance model (SNOWPACK) was applied to detect how the differences in the estimated values of the winter LAI and sky view fraction were reflected in simulated snow processes. In the simulations, an increase in LAI and a decrease in sky view fraction changed the snow surface energy balance by decreasing shortwave radiation input and increasing longwave radiation input. Changes in LAI and sky view fraction affected directly snow accumulation through altered throughfall fraction and indirectly snowmelt through the changed surface energy balance. Changes in LAI and sky view fraction had a greater impact on mean incoming radiation beneath the canopy than on other energy fluxes. Snowmelt was affected more than snow accumulation. The effect of canopy parameters on evaporation loss from intercepted snow was comparable with the effect of variation in governing meteorological variables such as precipitation intensity and air temperature. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Design Methodology for Grout Curtains Under Dams Founded on Rock     

Zhang  Suihan  Johansson  Fredrik  Stille  Håkan 《Geotechnical and Geological Engineering》2022,40(4):2167-2186

Geotechnical and Geological Engineering - Grout curtains are commonly constructed under dams to reduce the seepage through the rock foundation. In the design of grout curtains, empirical methods...  相似文献   

An assessment of estimates of integrated water vapor from ground-based GPS data     

B. Stoew  G. Elgered  J. M. Johansson 《Meteorology and Atmospheric Physics》2001,77(1-4):99-107

Summary A network of ground-based Global Positioning System (GPS) receivers is used to continuously obtain information on variations in the integrated water vapor (IWV) in the atmosphere. We use GPS data from 1996–1998 to compare the IWV estimates with radiosonde data. The spatial correlation of estimation errors is important when the GPS results are to be used in assimilation models. We study and model this effect by comparing the horizontal correlations of the IWV time series derived from the radiosonde network and the GPS data analysis. Under ideal conditions this method separates the IWV features from the underlying correlation function for the estimation errors in the GPS data. A sparse radiosonde network limits the quality of the obtained results. We foresee continued studies including more data and simulations of the errors associated with the GPS technique. Received November 21, 2000 Revised April 2, 2001  相似文献   

Inherited Landforms and Glacial Impact of Different Palaeosurfaces in Southwest Sweden   总被引：3，自引：0，他引：3  

Magnus Johansson  Mats Olvmo  & Karna Lidmar-Bergström 《Geografiska Annaler: Series A, Physical Geography》2001,83(1-2):67-89

Landforms are used as analytical tools to separate inherited features from the glacial impact on Precambrian basement rocks in southwest Sweden. The study covers three different palaeosurfaces, the sub-Cambrian peneplain (relative relief (r.r.) 0–20 m) with the character of a pediplain, an uplifted and dissected part of the sub-Cambrian peneplain (r.r. 5–40 m) and an etch-surface (r.r. 20–135 m), presumably sub-Mesozoic. The surfaces were recently re-exposed, probably due to a Neogene upheaval with some pre-glacial reshaping. Strong structural control and no alignment with glacial erosional directions other than those coinciding with structures, are arguments for etch processes as a most important agent for relief differentiation. This is strengthened by the occurrence of saprolite residues and etchforms in protected positions.
The glacial reshaping of the sub-Cambrian flat bedrock surfaces is negligible. The glacial impact becomes more evident in the uplifted and dissected parts of the peneplain and within the hilly sub-Mesozoic surface. The higher the initial relief the more effect of glacial erosion on individual hills, both on the abrading side, with formation of roches moutonnées, and on the plucking side. Detailed etchforms are preserved in protected positions in spite of erosion by a clearly wet-based ice. The magnitude of the Pleistocene glacial erosion is considerably less than the amplitude of the palaeorelief in the entire area.
Landscapes of areal glacial scouring have been described as comprising irregular depressions with intervening bosses scraped by ice and labelled 'knock and lochan' topography, but we suggest that an etched bedrock surface is a prerequisite for this type of landscape to develop.  相似文献   

Geotechnical properties of an attapulgite clay shale in northwestern nigeria     

Samuel Akinlabi Ola 《Engineering Geology》1982,19(1):1-13

The paper gives a brief review of the geology of the Iullemmeden Basin of northwestern Nigeria and how the stratigraphic sequence produces complex geotechnical problems. Mineralogical analysis showed the clay shale to be predominantly attapulgite. Detailed geotechnical properties of the clay showed the liquid limit to be greater than 200% and it depended significantly on treatment before testing. Very low maximum dry densities of 1137 kg/m³ (71 pcf), a high optimum moisture content of 41%, and a high compression index of 0.23 were obtained. The results presented also indicated that the attapulgite has very critical potential volume change. Results of the shear strength characteristics showed the effective cohesion to be zero in all the tests and a loss of strength of about 50% occurred as a result of decrease in the rate of strain.  相似文献   

Modelling of the physical behaviour of clay barriers close to water saturation     

Lennart Brgesson  Ola Karnland  Lars-Erik Johannesson 《Engineering Geology》1996,41(1-4):127-144

The physical properties of bentonite-based buffer materials for nuclear waste repositories have been investigated by a number of different laboratory tests. These tests have yielded a material model that is valid for conditions close to water saturation and is useful for describing: (a) the stress, strain and volume change behaviour; (b) the pore pressure and flow of water; and (c) the thermal and thermomechanical response.

The material model is based on the Drucker-Prager Plasticity model and a Porous Elastic Model. The effective stress concept and Darcy's law are applied and the swelling/consolidation and thermomechanical processes are coupled according to the separate mechanical properties of the pore water, the solids and the clay skeleton. The model can be used by the finite-element program ABAQUS.

The model has been tested in several laboratory and field verification tests. Comparison between measured and calculated behaviour shows that the general behaviour is described properly and several calculations of different scenarios have been made for the Swedish KBS 3 concept. However, certain processes, like the hysteresis effect at consolidation/swelling, the curved stress-strain relation at shearing, and the curved failure envelope, are not modelled in a perfectly accurate way and an improved material model is proposed here. It combines the behaviour of the Cam-clay model on the wet side with the more relevant plastic behaviour of a modified Drucker-Prager model with a curved failure envelope and the possibility to introduce strain softening after failure.

The paper presents some laboratory results that are the basis of the first model. It also shows the application of the model to finite-element calculations of some laboratory tests. Comparisons between the calculations and measured results expose some disadvantages of the model and a concept for an improved model is suggested.  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