Investigating the variance of downwind spray deposits
Holterman, H.J. - \ 2018
In: International Advances in Pesticide Application. - Warwick UK : Association of Applied Biologists Warwick Enterprise Park (Aspects of Applied Biology ) - p. 309 - 315.
bed sprayer - optimizing distribution - simulation - model - patternator - field trials - boom movements - spray deposits - variance - simulations
For bed-grown crops, ideally the spray is applied evenly to the bed only, while no spray should be applied onto the paths between the beds. Usually these criteria cannot be fulfilled easily. The current study describes the development and use of a model to design adequate set-ups of nozzles on a sprayer boom optimized for bed-grown crops. Spray patterns of various single nozzles at different boom heights have been measured on a patternator. The model combines these spray patterns while varying nozzle types, nozzle spacing and the position and angling of end nozzles. Examples are given for designs using Lechler Varioselect fourfold nozzle bodies to find optimal solutions for beds with widths between 1.1 and 1.5 m and boom heights of 0.2 to 0.6 m above the crop, while being able to apply different dose rates depending on crop canopy height. A large number of potential set-ups are simulated, but only relatively few meet the requirements that can be defined by the user.
Data from the Hot Serial Cereal Experiment for modeling wheat response to temperature: field experiments and AgMIP-Wheat multi-model simulations
Martre, Pierre ; Kimball, Bruce A. ; Ottman, Michael J. ; Wall, Gerard W. ; White, Jeffrey W. ; Asseng, Senthold ; Ewert, Frank ; Cammarano, Davide ; Maiorano, Andrea ; Aggarwal, Pramod K. ; Supit, I. ; Wolf, J. - \ 2018
Wageningen University & Research
wheat - heat stress - field experimental data - simulations
The dataset reported here includes the part of a Hot Serial Cereal Experiment (HSC) experiment recently used in the AgMIP-Wheat project to analyze the uncertainty of 30 wheat models and quantify their response to temperature. The HSC experiment was conducted in an open-field in a semiarid environment in the southwest USA. The data reported herewith include one hard red spring wheat cultivar (Yecora Rojo) sown approximately every six weeks from December to August for a two-year period for a total of 11 planting dates out of the 15 of the entire HSC experiment. The treatments were chosen to avoid any effect of frost on grain yields. On late fall, winter and early spring plantings temperature free-air controlled enhancement (T-FACE) apparatus utilizing infrared heaters with supplemental irrigation were used to increase air temperature by 1.3°C/2.7°C (day/night) with conditions equivalent to raising air temperature at constant relative humidity (i.e. as expected with global warming) during the whole crop growth cycle. Experimental data include local daily weather data, soil characteristics and initial conditions, detailed crop measurements taken at three growth stages during the growth cycle, and cultivar information. Simulations include both daily in-season and end-of-season results from 30 wheat models.
Data from global field experiments for potato simulations
Raymundo, Rubi ; Asseng, Senthold ; Prasad, Rishi ; Kleinwechter, Ulrich ; Condori, Bruno ; Bowen, Walter ; Wolf, J. ; Olesen, Jørgen E. ; Dong, Qiaoxue ; Zotarelli, Lincoln ; Gastelo, Manuel ; Alva, Ashok ; Travasso, Maria ; Arora, Vijay - \ 2018
Wageningen University & Research
potato - field experimental data - simulations
Estimation of spruce needle-leaf chlorophyll content based on DART and PARAS canopy reflectance models
Yanez Rausell, L. ; Malenovsky, Z. ; Rautiainen, M. ; Clevers, J.G.P.W. ; Lukes, P. ; Hanus, J. ; Schaepman, M.E. - \ 2015
IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing 8 (2015)4. - ISSN 1939-1404 - p. 1534 - 1544.
photon recollision probability - area index - spectral invariants - forest - prospect - stands - simulations - resolution - retrieval - lai-2000
Needle-leaf chlorophyll content (Cab) of a Norway spruce stand was estimated from CHRIS-PROBA images using the canopy reflectance simulated by the PROSPECT model coupled with two canopy reflectance models: 1) discrete anisotropic radiative transfer model (DART); and 2) PARAS. The DART model uses a detailed description of the forest scene, whereas PARAS is based on the photon recollision probability theory and uses a simplified forest structural description. Subsequently, statistically significant empirical functions between the optical indices ANCB670-720 and ANMB670-720 and the needle-leaf Cab content were established and then applied to CHRIS-PROBA data. The Cab estimating regressions using ANMB670_720 were more robust than using ANCB670-720 since the latter was more sensitive to LAI, especially in case of PARAS. Comparison between Cab estimates showed strong linear correlations between PARAS and DART retrievals, with a nearly perfect one-to-one fit when using ANMB670-720 (slope = 1.1, offset = 11 µg · cm-2). Further comparison with Cab estimated from an AISA Eagle image of the same stand showed better results for PARAS (RMSE = 2.7 µg · cm-2 for ANCB670-720; RMSE = 9.5 µg · cm-2 for ANMB670_720) than for DART (RMSE = 7.5 µg · cm-2 for ANCB670-720; RMSE = 23 µg · cm-2 for ANMB670-720). Although these results show the potential for simpler models like PARAS in estimating needle-leaf Cab from satellite imaging spectroscopy data, further analyses regarding parameterization of radiative transfer models are recommended.
Interactions among drainage flows, gravity waves and turbulence: a BLLAST case study
Román Cascón, C. ; Yagüe, C. ; Mahrt, L. ; Sastre, M. ; Steeneveld, G.J. ; Pardyjak, E. ; Boer, A. van de; Hartogensis, O.K. - \ 2015
Atmospheric Chemistry and Physics 15 (2015). - ISSN 1680-7316 - p. 9031 - 9047.
stable boundary-layer - intermittent turbulence - density-current - flux - field - wind - disturbances - simulations - stability - dynamics
The interactions among several stable-boundary-layer (SBL) processes occurring just after the evening transition of 2 July 2011 have been analysed using data from instruments deployed over the area of Lannemezan (France) during the Boundary Layer Late Afternoon and Sunset Turbulence (BLLAST) field campaign. The near-calm situation of the afternoon was followed by the formation of local shallow drainage flows (SDFs) of less than 10 m depth at different locations. The SDF stage ended with the arrival of a stronger wind over a deeper layer more associated with the mountain-plain circulation, which caused mixing and destruction of the SDFs. Several gravity-wave-related oscillations were also observed on different time series. Wavelet analyses and wave parameters were calculated from high resolution and accurate surface pressure data of an array of microbarometers. These waves propagated relatively long distances within the SBL. The effects of these phenomena on turbulent parameters (friction velocity and kinematic heat flux) have been studied through multi-resolution flux decomposition methods performed on high frequency data from sonic anemometers deployed at different heights and locations. With this method, we were able to detect the different time-scales involved in each turbulent parameter and separate them from wave contributions, which becomes very important when choosing averaging-windows for surface flux computations using eddy covariance methods. The extensive instrumentation allowed us to highlight in detail the peculiarities of the surface turbulent parameters in the SBL, where several of the noted processes were interacting and producing important variations in turbulence with height and between sites along the sloping terrain.
Competition between surface adsorption and folding of fibril-forming polypeptides
Ni, R. ; Kleijn, J.M. ; Cohen Stuart, M.A. ; Bolhuis, P.G. - \ 2015
Physical Review. E, Statistical nonlinear, and soft matter physics 91 (2015). - ISSN 2470-0045 - 5 p.
ionic-complementary peptide - fibrillization - biomaterials - simulations - proteins - fibers
Self-assembly of polypeptides into fibrillar structures can be initiated by planar surfaces that interact favorably with certain residues. Using a coarse-grained model, we systematically studied the folding and adsorption behavior of a ß -roll forming polypeptide. We find that there are two different folding pathways depending on the temperature: (i) at low temperature, the polypeptide folds in solution into a ß -roll before adsorbing onto the attractive surface; (ii) at higher temperature, the polypeptide first adsorbs in a disordered state and folds while on the surface. The folding temperature increases with increasing attraction as the folded ß -roll is stabilized by the surface. Surprisingly, further increasing the attraction lowers the folding temperature again, as strong attraction also stabilizes the adsorbed disordered state, which competes with folding of the polypeptide. Our results suggest that to enhance the folding, one should use a weakly attractive surface. They also explain the recent experimental observation of the nonmonotonic effect of charge on the fibril formation on an oppositely charged surface [C. Charbonneau et al., ACS Nano 8, 2328 (2014)].
AgMIP wheat pilot data 4 release
Asseng, S. ; Ewert, F. ; Martre, P. ; Supit, I. ; Wolf, J. - \ 2015
Wageningen UR, Wageningen
wheat - field experimental data - simulations - sensivity analysis - climate change impact
The data set includes a current representative management treatment from detailed, quality-tested sentinel field experiments with wheat from four contrasting environments including Australia, The Netherlands, India and Argentina. Measurements include local daily climate data (solar radiation, maximum and minimum temperature, precipitation, surface wind, dew point temperature, relative humidity, and vapor pressure), soil characteristics, frequent growth, nitrogen in crop and soil, crop and soil water and yield components. Simulations include results from 27 wheat models and a sensitivity analysis with 26 models and 30 years (1981-2010) for each location, for elevated atmospheric CO2 and temperature changes, a heat stress sensitivity analysis at anthesis, and a sensitivity analysis with soil and crop management variations and a Global Climate Model end-century scenario.
Multimodel ensembles of wheat growth: Many models are better than one
Martre, P. ; Wallach, D. ; Asseng, S. ; Ewert, F. ; Jones, J.W. ; Rötter, R.P. ; Boote, K.J. ; Ruane, A.C. ; Thorburn, P. ; Cammarano, D. ; Hatfield, J.L. ; Rosenzweig, C. ; Aggarwal, P.K. ; Angula, C. ; Basso, B. ; Bertuzzi, P. ; Biernath, C. ; Brisson, N. ; Challinor, A. ; Doltra, J. ; Gayler, S. ; Goldberg, R.A. ; Grant, R.F. ; Heng, L. ; Hooker, J. ; Hunt, L.A. ; Ingwersen, J. ; Izaurralde, C. ; Kersebaum, K.C. ; Mueller, C. ; Kumar, S. ; Nendel, C. ; O'Leary, G.J. ; Olesen, J.E. ; Osborne, T.M. ; Palosuo, T. ; Priesack, E. ; Ripoche, D. ; Semenov, M.A. ; Shcherbak, I. ; Steduto, P. ; Stöckle, C.O. ; Stratonovitch, P. ; Streck, T. ; Supit, I. ; Tao, Fulu ; Travasso, M. ; Waha, K. ; White, J.W. ; Wolf, J. - \ 2015
Global Change Biology 21 (2015)2. - ISSN 1354-1013 - p. 911 - 925.
climate-change - crop production - impacts - yield - simulations - calibration - australia - billion - europe - grain
Crop models of crop growth are increasingly used to quantify the impact of global changes due to climate or crop management. Therefore, accuracy of simulation results is a major concern. Studies with ensembles of crop models can give valuable information about model accuracy and uncertainty, but such studies are difficult to organize and have only recently begun. We report on the largest ensemble study to date, of 27 wheat models tested in four contrasting locations for their accuracy in simulating multiple crop growth and yield variables. The relative error averaged over models was 24-38% for the different end-of-season variables including grain yield (GY) and grain protein concentration (GPC). There was little relation between error of a model for GY or GPC and error for in-season variables. Thus, most models did not arrive at accurate simulations of GY and GPC by accurately simulating preceding growth dynamics. Ensemble simulations, taking either the mean (e-mean) or median (e-median) of simulated values, gave better estimates than any individual model when all variables were considered. Compared to individual models, e-median ranked first in simulating measured GY and third in GPC. The error of e-mean and e-median declined with an increasing number of ensemble members, with little decrease beyond 10 models. We conclude that multimodel ensembles can be used to create new estimators with improved accuracy and consistency in simulating growth dynamics. We argue that these results are applicable to other crop species, and hypothesize that they apply more generally to ecological system models.
Optimization and spatial pattern of large-scale aquifer thermal energy storage
Sommer, W.T. ; Valstar, J. ; Leusbrock, I. ; Grotenhuis, J.T.C. ; Rijnaarts, H.H.M. - \ 2015
Applied Energy 137 (2015). - ISSN 0306-2619 - p. 322 - 337.
source heat-pumps - geothermal systems - ground-water - transport - consumption - simulations - performance - buildings - solute
Aquifer thermal energy storage (ATES) is a cost-effective technology that enables the reduction of energy use and CO2 emissions associated with the heating and cooling of buildings by storage and recovery of large quantities of thermal energy in the subsurface. Reducing the distance between wells in large-scale application of ATES increases the total amount of energy that can be provided by ATES in a given area. However, due to thermal interference the performance of individual systems can decrease. In this study a novel method is presented that can be used to (a) determine the impact of thermal interference on the economic and environmental performance of ATES and (b) optimize well distances in large-scale applications. The method is demonstrated using the hydrogeological conditions of Amsterdam, Netherlands. Results for this case study show that it is cost-effective to allow a limited amount of thermal interference, such that 30–40% more energy can be provided in a given area compared to the case in which all negative thermal interference is avoided. Sensitivity analysis indicates that optimal well distance is moderately insensitive to changes in hydrogeological and economic conditions. Maximum economic benefit compared to conventional heating and cooling systems on the other hand is sensitive, especially to changes in the gas price and storage temperatures.
Moisture transport in swelling media modelled with a Lattice Boltzmann scheme having a deforming lattice
Sman, R.G.M. van der - \ 2014
Journal of Food Engineering 124 (2014). - ISSN 0260-8774 - p. 54 - 63.
non-brownian suspensions - diffusion lattice - water transport - flow - simulations - profiles - kinetics - food - gels - validation
In this paper we present a novel numerical scheme for simulating the one-dimensional deformation of hydrogel material due to drying or rehydration. The scheme is based on the versatile Lattice Boltzmann method, which has been extended such that the computational grid (lattice) deforms due to shrinkage or swelling. This property of a deforming grid is new to the lattice Boltzmann method, and a detailed description of this new method is given. Via simulations we show that self-similar moisture concentration profiles occur in two periods in both drying and swelling processes: the penetration period and the regular regime. Given the property of self-similarity, we have been able to formulate a reduced-order model for the regular regime of swelling.
Forest summer albedo is sensitive to species and thinning: how should we account for this in Earth system models?
Otto, J. ; Berveiller, D. ; Bréon, F.M. ; Delpierre, N. ; Geppert, G. ; Granier, A. ; Jans, W.W.P. ; Knohl, A. ; Schelhaas, M.J. ; Moors, E.J. - \ 2014
Biogeosciences 11 (2014). - ISSN 1726-4170 - p. 2411 - 2427.
leaf-area index - boreal forest - reflectance models - canopy reflectance - carbon-cycle - climate - radiation - stands - simulations - variability
Although forest management is one of the instruments proposed to mitigate climate change, the relationship between forest management and canopy albedo has been ignored so far by climate models. Here we develop an approach that could be implemented in Earth system models. A stand-level forest gap model is combined with a canopy radiation transfer model and satellite-derived model parameters to quantify the effects of forest thinning on summertime canopy albedo. This approach reveals which parameter has the largest affect on summer canopy albedo: we examined the effects of three forest species (pine, beech, oak) and four thinning strategies with a constant forest floor albedo (light to intense thinning regimes) and five different solar zenith angles at five different sites (40° N 9° E–60° N 9° E). During stand establishment, summertime canopy albedo is driven by tree species. In the later stages of stand development, the effect of tree species on summertime canopy albedo decreases in favour of an increasing influence of forest thinning. These trends continue until the end of the rotation, where thinning explains up to 50% of the variance in near-infrared albedo and up to 70% of the variance in visible canopy albedo. The absolute summertime canopy albedo of all species ranges from 0.03 to 0.06 (visible) and 0.20 to 0.28 (near-infrared); thus the albedo needs to be parameterised at species level. In addition, Earth system models need to account for forest management in such a way that structural changes in the canopy are described by changes in leaf area index and crown volume (maximum change of 0.02 visible and 0.05 near-infrared albedo) and that the expression of albedo depends on the solar zenith angle (maximum change of 0.02 visible and 0.05 near-infrared albedo). Earth system models taking into account these parameters would not only be able to examine the spatial effects of forest management but also the total effects of forest management on climate.
Thermal performance and heat transport in aquifer thermal energy storage
Sommer, W.T. ; Doornenbal, P.J. ; Drijver, B.C. ; Gaans, P.F.M. van; Leusbrock, I. ; Grotenhuis, J.T.C. ; Rijnaarts, H.H.M. - \ 2014
Hydrogeology Journal 22 (2014)1. - ISSN 1431-2174 - p. 263 - 279.
temperature sensing data - systems - simulations
Aquifer thermal energy storage (ATES) is used for seasonal storage of large quantities of thermal energy. Due to the increasing demand for sustainable energy, the number of ATES systems has increased rapidly, which has raised questions on the effect of ATES systems on their surroundings as well as their thermal performance. Furthermore, the increasing density of systems generates concern regarding thermal interference between the wells of one system and between neighboring systems. An assessment is made of (1) the thermal storage performance, and (2) the heat transport around the wells of an existing ATES system in the Netherlands. Reconstruction of flow rates and injection and extraction temperatures from hourly logs of operational data from 2005 to 2012 show that the average thermal recovery is 82% for cold storage and 68% for heat storage. Subsurface heat transport is monitored using distributed temperature sensing. Although the measurements reveal unequal distribution of flow rate over different parts of the well screen and preferential flow due to aquifer heterogeneity, sufficient well spacing has avoided thermal interference. However, oversizing of well spacing may limit the number of systems that can
Including climate change projections in probabilistic flood risk assessment
Ward, P.J. ; Pelt, S.C. van; Keizer, O. de; Aerts, J.C.J.H. ; Beersma, J.J. ; Hurk, B.J.J.M. van den - \ 2014
Journal of Flood Risk Management 7 (2014)2. - ISSN 1753-318X - p. 141 - 151.
klimaatverandering - overstromingen - risicoschatting - modellen - climatic change - floods - risk assessment - models - rhine basin - model - precipitation - uncertainty - simulations - decisions
This paper demonstrates a framework for producing probabilistic flood risk estimates, focusing on two sections of the Rhine River. We used an ensemble of six (bias-corrected) regional climate model (RCM) future simulations to create a 3000-year time-series through resampling. This was complemented with 12 global climate model (GCM)-based future time-series, constructed by resampling observed time-series of daily precipitation and temperature and modifying these to represent future climate conditions using an advanced delta change approach. We used the resampled time-series as input in the hydrological model Hydrologiska Byråns Vattenbalansavdelning (HBV)-96 to simulate daily discharge and extreme discharge quantiles for return periods up to 3000 years. To convert extreme discharges to estimates of flood damage and risk, we coupled a simple inundation model with a damage model. We then fitted probability density functions (PDFs) for the RCM, GCM, and combined ensembles. The framework allows for the assessment of the probability distribution of flood risk under future climate scenario conditions. Because this paper represents a demonstration of a methodological framework, the absolute figures should not be used in decision making at this time.
Implications of alternative assumptions regarding future air pollution control in scenarios similar to the Representative Concentration Pathways
Chuwah, C.D. ; Noije, T. van; Vuuren, D.P. van; Hazeleger, W. ; Strunk, A. ; Deetman, S. ; Beltran, A.M. ; Vliet, J. van de - \ 2013
Atmospheric Environment 79 (2013). - ISSN 1352-2310 - p. 787 - 801.
intercomparison project accmip - greenhouse-gas concentrations - atmospheric chemistry - tropospheric ozone - next-generation - climate-change - model - emissions - stabilization - simulations
The uncertain, future development of emissions of short-lived trace gases and aerosols forms a key factor for future air quality and climate forcing. The Representative Concentration Pathways (RCPs) only explore part of this range as they all assume that worldwide ambitious air pollution control policies will be implemented. In this study, we explore how different assumptions on future air pollution policy and climate policy lead to different concentrations of air pollutants for a set of RCP-like scenarios developed using the IMAGE model. These scenarios combine low and high air pollution variants of the scenarios with radiative forcing targets in 2100 of 2.6 W m(-2) and 6.0 W m(-2). Simulations using the global atmospheric chemistry and transport model TM5 for the present-day climate show that both climate mitigation and air pollution control policies have large-scale effects on pollutant concentrations, often of similar magnitude. If no further air pollution policies would be implemented, pollution levels could be considerably higher than in the RCPs, especially in Asia. Air pollution control measures could significantly reduce the warming by tropospheric ozone and black carbon and the cooling by sulphate by 2020, and in the longer term contribute to enhanced warming by methane. These effects tend to cancel each other on a global scale. According to our estimates the effect of the worldwide implementation of air pollution control measures on the total global mean direct radiative forcing in 2050 is +0.09 W m(-2) in the 6.0 W m(-2) scenario and -0.16 W m(-2) in the 2.6 W m(-2) scenario. (C) 2013 Elsevier Ltd. All rights reserved.
Investigation of Lattice Boltzmann wetting boundary conditions for capillaries with irregular polygonal cross-section
Sman, R.G.M. van der - \ 2013
Computer Physics Communications 184 (2013)12. - ISSN 0010-4655 - p. 2751 - 2760.
binary fluids - porous-media - simulations - flows - model - equation - configurations - dynamics - schemes
We have investigated the performance of an alternative wetting boundary condition for complex geometries in a phase field Lattice Boltzmann scheme, which is an alternative to the commonly used formulation by Yeomans and coworkers. Though our boundary condition is much simpler in its implementation, all investigated schemes show proper droplet spreading behaviour following the Cox-Voinov law. Still, numerical artefacts like spurious velocities or chequer board effects in the pressure field can be significantly reduced by the use of a two-relaxation-time (TRT) scheme, likewise recent studies by the Yeomans group. The outstanding property of our implementation is the presence of an (artificial) thin wetting layer, which influences the relation between the saturation (S-w) and capillary pressure p(cap) in channels with irregular polygonal cross section. The p(cap) (S-w) relation from our simulation follows the shifted-Young-Laplace (sYL) law, showing that the physics of this wetting layer is similar to precursor films due to Van der Waals forces. With the knowledge of the thickness of the wetting layer, simulation results can be translated back to realistic pore configurations with thinner wetting layers. (C) 2013 Elsevier B.V. All rights reserved.
Interplay between folding and assembly of fibril-forming polypeptides
Ni, R. ; Abeln, S. ; Schor, M. ; Cohen Stuart, M.A. ; Bolhuis, P.G. - \ 2013
Physical Review Letters 111 (2013)5. - ISSN 0031-9007 - 5 p.
protein - simulations - disease
Polypeptides can self-assemble into hierarchically organized fibrils consisting of a stack of individually folded polypeptides driven together by hydrophobic interaction. Using a coarse-grained model, we systematically studied this self-assembly as a function of temperature and hydrophobicity of the residues on the outside of the building block. We find the self-assembly can occur via two different pathways-a random aggregation-folding route and a templated-folding process-thus indicating a strong coupling between folding and assembly. The simulation results can explain experimental evidence that assembly through stacking of folded building blocks is rarely observed, at the experimental concentrations. The model thus provides a generic picture of hierarchical fibril formation
Atmospheric blocking in a high resolution climate model: influences of mean state, orography and eddy forcing
Berckmans, J.N.J. ; Woollings, T. ; Demory, M. ; Vidale, P. ; Roberts, M. - \ 2013
Atmospheric Science Letters 14 (2013)1. - ISSN 1530-261X - p. 34 - 40.
eddies - flow - propagation - simulations - patterns - project
An underestimate of atmospheric blocking occurrence is a well-known limitation of many climate models. This article presents an analysis of Northern Hemisphere winter blocking in an atmospheric model with increased horizontal resolution. European blocking frequency increases with model resolution, and this results from an improvement in the atmospheric patterns of variability as well as a simple improvement in the mean state. There is some evidence that the transient eddy momentum forcing of European blocks is increased at high resolution, which could account for this. However, it is also shown that the increase in resolution of the orography is needed to realise the improvement in blocking, consistent with the increase in height of the Rocky Mountains acting to increase the tilt of the Atlantic jet stream and giving higher mean geopotential heights over northern Europe. Blocking frequencies in the Pacific sector are also increased with atmospheric resolution, but in this case the improvement in orography actually leads to a decrease in blocking
Evapotranspiration amplifies European summer drought
Teuling, A.J. ; Loon, A.F. van; Seneviratne, S.I. ; Lehner, I. ; Aubinet, M. ; Heinesch, B. ; Bernhofer, C. ; Grünwald, T. ; Prasse, H. ; Spank, U. - \ 2013
Geophysical Research Letters 40 (2013)10. - ISSN 0094-8276 - p. 2071 - 2075.
forest - simulations - exchange - carbon - scale
Drought is typically associated with a lack of precipitation, whereas the contribution of evapotranspiration and runoff to drought evolution is not well understood. Here we use unique long-term observations made in four headwater catchments in central and western Europe to reconstruct storage anomalies and study the drivers of storage anomaly evolution during drought. We provide observational evidence for the “drought-paradox” in that region: a consistent and significant increase in evapotranspiration during drought episodes, which acts to amplify the storage anomalies. In contrast, decreases in runoff act to limit storage anomalies. Our findings stress the need for the correct representation of evapotranspiration and runoff processes in drought indices.
Transient critical flux due to coupling of fouling mechanisms during crossflow microfiltration of beer
Sman, R.G.M. van der; Vollebregt, H.M. - \ 2013
Journal of Membrane Science 435 (2013). - ISSN 0376-7388 - p. 21 - 37.
pressure-driven flow - concentration polarization - concentrated suspensions - colloidal suspensions - particle migration - yeast suspensions - model - filtration - shear - simulations
Models of fouling during beer clarification, previously validated for dead-end filtration, are combined with a model describing the build-up of the cake layer of yeast cells via shear-induced diffusion induced by crossflow. For describing shear-induced diffusion, we have taken the most recent model, which is based on the effective temperature concept. Via scale analysis we show that (1) effects of polydispersity are negligible and (2) the cake layer growth model still be reduced to the earlier model of Romero and Davis, albeit with different parameter values. The adapted Romero and Davis model has been coupled to the earlier reviewed models of fouling by aggregates and macromolecules, for which we have performed computer simulations. In this paper we report on striking results on the downstream movement of the critical point, xcr, where the cake layer starts building up. We show that this is due to strong coupling between the cake layer build-up and the other fouling modes. Hence, this means that the concept of critical flux can not be viewed any more as a time-invariant value. This finding has implications beyond the application of beer, and especially for biotechnological broths which have similar composition of beer.
Are Greenhouse Gas Signals of Northern Hemisphere winter
Ulbrich, U. ; Leckebusch, G.C. ; Grieger, J. ; Kew, S.F. - \ 2013
Meteorologische Zeitschrift 22 (2013). - ISSN 0941-2948 - p. 61 - 68.
storm-tracks - climate-change - numerical scheme - reanalysis data - digital data - life-cycle - simulations - atlantic - era-40 - model
For Northern Hemisphere extra-tropical cyclone activity, the dependency of a potential anthropogenic climate change signal on the identification method applied is analysed. This study investigates the impact of the used algorithm on the changing signal, not the robustness of the climate change signal itself. Using one single transient AOGCM simulation as standard input for eleven state-of-the-art identification methods, the patterns of model simulated present day climatologies are found to be close to those computed from re-analysis, independent of the method applied. Although differences in the total number of cyclones identified exist, the climate change signals (IPCC SRES A1B) in the model run considered are largely similar between methods for all cyclones. Taking into account all tracks, decreasing numbers are found in the Mediterranean, the Arctic in the Barents and Greenland Seas, the mid-latitude Pacific and North America. Changing patterns are even more similar, if only the most severe systems are considered: the methods reveal a coherent statistically significant increase in frequency over the eastern North Atlantic and North Pacific. We found that the differences between the methods considered are largely due to the different role of weaker systems in the specific methods.