Friction velocity scaling in wind wave generation     

Peter A. E. M. Janssen  Gerbrand J. Komen  Willem J. P. De Voogt 《Boundary-Layer Meteorology》1987,38(1-2):29-35

This note is devoted to the problem of the appropriate scaling of parameters relevant for sea waves, such as wave height, peak frequency, duration, and fetch. In the past, the growth of sea waves has often been analysed in terms of the wind velocity at a fixed height, despite the fact that many authors have stressed the importance of scaling with the friction velocity. This problem would be immaterial if the ratio between the friction velocity and the wind speed at a fixed height were a constant. There is, however, ample evidence that this ratio increases with wind speed (Smith and Banke, 1975; Smith, 1980), in agreement with dimensional considerations by Charnock (1955) on the friction height. As a result, the scaling problem is an important one. In this note we conjecture that the correct procedure is to scale wave parameters with friction velocity, and we discuss experimental evidence for the correctness of this conjecture. Comparing two independent datasets (JONSWAP and KNMI), we find some evidence supporting our ideas. Further confirmation remains desirable, however, and suggestions are made as to how this might be obtained.  相似文献   

Evaluating a Model of Evaporation and Transpiration with Observations in a Partially Wet Douglas-Fir Forest   总被引：1，自引：0，他引：1  

Fred C. Bosveld  Willem Bouten 《Boundary-Layer Meteorology》2003,108(3):365-396

The Penman–Monteith equation is extended to describe evaporation of intercepted rain, transpiration and the interaction between these processes in a single explicit function. This single-layer model simulates the effects of heat exchange, stomatal blocking and changed humidity deficit close to the canopy as a function of canopywater storage. Evaporation depends on the distribution of water over the canopy and the energy exchange between wet and dry parts. Transpiration depends on the dry canopy surface resistance that is described with a Jarvis-type response. The explicit functions obtained for water vapour fluxes facilitate a straightforward identificationof the various processes. Canopy water storage amounts and xylem sapflow were measured simultaneously during drying episodes after rainfall in a dense, partially wet, Douglas-fir forest. Estimates of evaporation and transpiration rates are derived from these observations. The analysis shows that evaporation induced transpirationreduction is mainly caused by energy consumption. Changes in water vapour deficit have a minor effect due to a compensating stomatal reaction. The remaining difference between observed and modelled transpiration reduction can be attributed to partial blocking of stomata by the water layer.  相似文献   

Modeling the binding of fulvic acid by goethite: the speciation of adsorbed FA molecules   总被引：1，自引：0，他引：1  

Jeroen D. Filius  David G. Lumsdon  Willem H. van Riemsdijk 《Geochimica et cosmochimica acta》2003,67(8):1463-1474

Under natural conditions, the adsorption of ions at the solid-water interface may be strongly influenced by the adsorption of organic matter. In this paper, we describe the adsorption of fulvic acid (FA) by metal(hydr)oxide surfaces with a heterogeneous surface complexation model, the ligand and charge distribution (LCD) model. The model is a self-consistent combination of the nonideal competitive adsorption (NICA) equation and the CD-MUSIC model. The LCD model can describe simultaneously the concentration, pH, and salt dependency of the adsorption with a minimum of only three adjustable parameters. Furthermore, the model predicts the coadsorption of protons accurately for an extended range of conditions. Surface speciation calculations show that almost all hydroxyl groups of the adsorbed FA molecules are involved in outer sphere complexation reactions. The carboxylic groups of the adsorbed FA molecule form inner and outer sphere complexes. Furthermore, part of the carboxylate groups remain noncoordinated and deprotonated.  相似文献   

Paleolimnological evidence for increased landslide activity due to forest clearing and land-use since 3600 cal BP in the western Swiss Alps     

Florence Dapples  André F. Lotter  Jacqueline F.N. van Leeuwen  Willem O. van der Knaap  Sophia Dimitriadis  Daniel Oswald 《Journal of Paleolimnology》2002,27(2):239-248

Schwarzsee is located in the western Swiss Alps, in a region that has been affected by numerous landslides during the Holocene, as evidenced by geological surveys. Lacustrine sediments were cored to a depth of 13 m. The vegetation history of the lake's catchment was reconstructed and investigated to identify possible impacts on slope stability. The pollen analyses record development of forest cover during the middle and late Holocene, and provide strong evidence for regional anthropogenic influence such as forest clearing and agricultural activity. Vegetation change is characterized by continuous landscape denudation that begins at ca. 4300 cal. yrs BP, with five distinct pulses of increased deforestation, at 3650, 2700, 1500, 900, and 450 cal. yrs BP. Each pulse can be attributed to increased human impact, recorded by the appearance or increase of specific anthropogenic indicator plant taxa. These periods of intensified deforestation also appear to be correlated with increased landslide activity in the lake's catchment and increased turbidite frequency in the sediment record. Therefore, this study gives new evidence for a strong influence of vegetation changes on slope stability during the middle and late Holocene in the western Swiss Alps, and may be used as a case study for anthropogenically induced landslide activity.  相似文献   

Groundwater chemistry of Al under Dutch sandy soils: Effects of land use and depth     

Ellen P.M.J. Fest  Erwin J.M. Temminghoff  Jasper Griffioen  Bas Van Der Grift  Willem H. Van Riemsdijk 《Applied Geochemistry》2007

Aluminium has received great attention in the second half of the 20th century, mainly in the context of the acid rain problem mostly in forest soils. In this research the effect of land use and depth of the groundwater on Al, pH and DOC concentration in groundwater under Dutch sandy soils has been studied. Both pH and DOC concentration play a major role in the speciation of Al in solution. Furthermore, the equilibrium with mineral phases like gibbsite, amorphous Al(OH)₃ and imogolite, has been considered. Agricultural and natural land use were expected to have different effects on the pH and DOC concentration, which in turn could influence the total Al concentration and the speciation of Al in groundwater at different depths (phreatic, shallow and deep). An extensive dataset (n = 2181) from the national and some provincial monitoring networks on soil and groundwater quality was used. Land use type and groundwater depth did influence the pH, and Al and DOC concentrations in groundwater samples. The Al concentration ranged from <0.4 μmol L⁻¹ at pH > 7 to 1941 μmol L⁻¹ at pH < 4; highest Al concentrations were found for natural-phreatic groundwater. The DOC concentration decreased and the median pH increased with depth of the groundwater. Natural-phreatic groundwater showed lower pH than the agricultural-phreatic groundwater. Highest DOC concentrations were found for the agricultural-phreatic groundwater, induced by the application of organic fertilizers. Besides inorganic complexation, the NICA-Donnan model was used to calculate Al³⁺ concentrations for complexation with DOC. Below pH 4.5 groundwater samples were mainly in disequilibrium with a mineral phase. This disequilibrium is considered to be the result of kinetic constraints or equilibrium with organic matter. Log K values were derived by linear regression and were close to theoretical values for Al(OH)₃ minerals (e.g. gibbsite or amorphous Al(OH)₃), except for natural-phreatic groundwater for which lower log K values were found. Complexation of Al with DOC is shown to be an important factor for the Al concentrations, especially at high DOC concentrations as was found for agricultural-phreatic groundwater.  相似文献   

Spectrophotometry of Jupiter     

Willem Wamsteker  Theodore D. Fay  Bill J. Duncan 《Icarus》1976,29(2):315-319

Spectrophotometric maps of Jupiter were made between 24 and 27(UT) November 1974 on the McMath Solar Telescope at Kitt Peak National Observatory. We report a comparison between observed scaled reflectivities of the Jovian North Tropical Zone and the North Equatorial Belt at System II longitudes between 195 and 205 degrees. The belt/zone reflectivity ratios between 430 and 740nm are related to the optical transmission curves of the organic and/or sulfur polymers synthesized by Khare and Sagan in a simulated Jovian atmosphere.  相似文献   

Estimating the deep seepage component of the hillslope and catchment water balance within a measurement uncertainty framework     

Chris B. Graham  Willem van Verseveld  Holly R. Barnard  Jeffrey J. McDonnell 《水文研究》2010,24(25):3631-3647

Deep seepage is a term in the hillslope and catchment water balance that is rarely measured and usually relegated to a residual in the water balance equation. While recent studies have begun to quantify this important component, we still lack understanding of how deep seepage varies from hillslope to catchment scales and how much uncertainty surrounds its quantification within the overall water balance. Here, we report on a hillslope water balance study from the H. J. Andrews Experimental Forest in Oregon aimed at quantifying the deep seepage component where we irrigated a 172‐m² section of hillslope for 24·4 days at 3·6 ± 3 mm/h. The objective of this experiment was to close the water balance, identifying the relative partitioning of, and uncertainties around deep seepage and the other measured water balance components of evaporation, transpiration, lateral subsurface flow, bedrock return flow and fluxes into and out of soil profile storage. We then used this information to determine how the quantification of individual water balance components improves our understanding of key hillslope processes and how uncertainties in individual measurements propagate through the functional uses of the measurements into water balance components (i.e. meteorological measurements propagated through potential evapotranspiration estimates). Our results show that hillslope scale deep seepage composed of 27 ± 17% of applied water. During and immediately after the irrigation experiment, a significant amount of the irrigation water could not be accounted for. This amount decreased as the measurement time increased, declining from 28 ± 16% at the end of the irrigation to 20 ± 21% after 10 days drainage. This water is attributed to deep seepage at the catchment scale. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

The value of remotely sensed surface soil moisture for model calibration using SWAT          下载免费PDF全文

Dipangkar Kundu  R. Willem Vervoort  Floris F. van Ogtrop 《水文研究》2017,31(15):2764-2780

Remotely sensed (RS) data can add value to a hydrological model calibration. Among this, RS soil moisture (SM) data have mostly been assimilated into conceptual hydrological models using various transformed variable or indices. In this study, raw RS surface SM is used as a calibration variable in the Soil and Water Assessment Tool model. This means the SM values were not transformed into another variable (e.g., soil water index and root zone SM index). Using a nested catchment, calibration based only on RS SM and optimizing model parameters sensitive to SM using particle swarm optimization improved variations in streamflow predictions at some of the gauging stations compared to the uncalibrated model. This highlighted part of the catchments where the SM signal directly influenced the flow distribution. Additionally, highlighted high and low flow signals were mostly influenced. The seasonal breakdown indicates that the SM signal is more useful for calibrating in wetter seasons and in areas with higher variations in elevation. The results identified that calibration only on RS SM improved the general rainfall–runoff response simulation by introducing delays but cannot correct the overall routing effect. Furthermore, catchment characteristics (e.g., land use, elevation, soil types, and precipitation) regulating SM variation in different seasons highlighted by the model calibration are identified. This provides further opportunities to improve model parameterization.  相似文献   

Humic substance charge determination by titration with a flexible cationic polyelectrolyte   总被引：1，自引：0，他引：1  

Wen-Feng Tan  Willem Norde  Luuk K. Koopal 《Geochimica et cosmochimica acta》2011,75(19):5749-5761

The anionic charge of humic substances (HS) plays a major role in the interaction of HS with other components. Therefore, the potential of the polyelectrolyte titration technique to obtain the charge density of HS in simple 1-1 electrolyte solutions has been investigated. Titrations are carried out with an automatic titrator combined with the “Mütek particle charge detector” which allows determination of the Mütek potential and the pH as a function of the added amount of titrant which is a solution of poly-diallyldimethylammonium chloride (polyDADMAC), a cationic strong polyelectrolyte. When the Mütek potential reverses its sign the iso-electric point (IEP) of the polyDADMAC-HS complex is reached. The polyDADMAC/HS mass ratio at the IEP gives information on the HS charge density and from the pH changes in solution an estimate of the charge regulation in the HS-polyDADMAC complex can be obtained. In general, for polyDADMAC-HS complexes an increase in the dissociation of the acid groups of HS is found (charge regulation). The charge regulation decreases with increasing concentration of 1-1 background electrolyte. Cation incorporation can be neglected at 1-1 electrolyte concentrations ? 1 mmol L⁻¹ and a 1-1 stoichiometry exists between the polyDADMAC and HS charge. However, at these low salt concentrations the charge regulation is substantial. A detailed analysis of purified Aldrich humic acid (PAHA) at pH 5 and a range of KCl concentrations reveals that the anionic charge of PAHA in the complex increases at 5 mmol L⁻¹ KCl by 30% and at 150 mmol L⁻¹ KCl by 12%. On the other hand, increasing amounts of K⁺ become incorporated in the complex: at 5 mmol L⁻¹ KCl 5% and at 150 mmol L⁻¹ KCl 24% of the PAHA charge is balanced by K⁺. By comparing at pH 5 the mass ratios polyDADMAC/PAHA in the complex at the IEP with the theoretical mass ratios of polyDADMAC/PAHA required to neutralize PAHA in the absence of charge regulation and K⁺ incorporation, it is found that at 50 mmol L⁻¹ KCl the extra negative charge due to the interaction between polyDADMAC and PAHA is just compensated by K⁺ incorporation in the complex. Therefore, a pseudo 1-1 stoichiometry exists at about 50 mmol L⁻¹ 1-1 electrolyte concentration and only at this salt concentration polyDADMAC titrations and conventional proton titrations give identical results. Most likely this is also true for other HA samples and other pH values. For FA further study is required to reveal the conditions for which polyDADMAC and proton titrations give identical results.  相似文献   

VLBI imaging of OH absorption: the puzzle of the nuclear region of NGC 3079     

Yoshiaki Hagiwara  Hans-Rainer Klöckner  Willem Baan 《Monthly notices of the Royal Astronomical Society》2004,353(4):1055-1063

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