scholarly journals Analysis of effective resistance calculation methods and their effect on modelling evapotranspiration in two different patches of vegetation in semi-arid SE Spain

2007 ◽  
Vol 11 (5) ◽  
pp. 1529-1542 ◽  
Author(s):  
A. Were ◽  
L. Villagarcía ◽  
F. Domingo ◽  
L. Alados-Arboledas ◽  
J. Puigdefábregas
Keyword(s):  
Aerodynamic Resistance ◽  
Surface Fluxes ◽  
Effective Parameters ◽  
Effective Surface ◽  
Se Spain ◽  
Retama Sphaerocarpa ◽  
In Series ◽  
Eddy Covariance System ◽  
Patch Scale ◽  
Monteith Equation

Abstract. Effective parameters are of major importance in modelling surface fluxes at different scales of spatial heterogeneity. Different ways to obtain these effective parameters for their use in meso-scale and GCM models have been studied. This paper deals with patch-scale heterogeneity, where effective resistances were calculated in two patches with different vegetation (Retama sphaerocarpa (L.) Boiss shrubs, and herbaceous plants) using different methods: aggregating soil and plant resistances in parallel, in series or by an average of both. Effective aerodynamic resistance was also calculated directly from patch fluxes. To assess the validity of the different methods used, the Penman-Monteith equation was used with effective resistances to estimate the total λE for each patch. The λE estimates found for each patch were compared to Eddy Covariance system measurements. Results showed that for effective surface resistances, parallel aggregation of soil and plant resistances led to λE estimates closer to the measured λE in both patches (differences of around 10%). Results for effective aerodynamic resistances differed depending on the patch considered and the method used to calculate them. The use of effective aerodynamic resistances calculated from fluxes provided less accurate estimates of λE compared to the measured values, than the use of effective aerodynamic resistances aggregated from soil and plant resistances. The results reported in this paper show that the best way of aggregating soil and plant resistances depends on the type of resistance, and the type of vegetation in the patch.

scholarly journals Analysis of effective resistance calculation methods and their effect on modelling evapotranspiration in two different patches of vegetation in semi-arid SE Spain

2007 ◽  
Vol 4 (1) ◽  
pp. 243-286 ◽  
Author(s):  
A. Were ◽  
L. Villagarcía ◽  
F. Domingo ◽  
L. Alados-Arboledas ◽  
J. Puigdefábregas
Keyword(s):  
Aerodynamic Resistance ◽  
Surface Fluxes ◽  
Effective Parameters ◽  
Retama Sphaerocarpa ◽  
Sparse Vegetation ◽  
In Series ◽  
Eddy Covariance System ◽  
Patch Scale ◽  
Monteith Equation ◽  
Semi Arid

Abstract. Effective parameters are of major importance in modelling surface fluxes at different scales of spatial heterogeneity. Different ways to obtain these effective parameters for their use in meso-scale and GCM models have been studied. This paper deals with patch-scale heterogeneity, where effective resistances were calculated in two patches with different vegetation (Retama sphaerocarpa (L.) Boiss shrubs, and herbaceous plants) using different methods: aggregating soil and plant resistances in parallel, in series or by an average of both. Effective aerodynamic resistance was also calculated directly from patch fluxes. To assess the validity of the different methods used, the Penman-Monteith equation was used with effective resistances to estimate the total λ E for each patch. The λ E estimates found for each patch were compared to Eddy Covariance system measurements. Results showed that for effective surface resistances, parallel aggregation of soil and plant resistances led to λ E estimates closer to the measured λ E in both patches (differences of around 10%). This may be due to the fact that in semi-arid areas, with very sparse vegetation, soil resistances are much higher than plant resistances, and therefore parallel aggregation attenuates the effect of the high soil resistances on λ E modelling. Results for effective aerodynamic resistances differed depending on the patch considered and the method used to calculate them. The use of effective aerodynamic resistance calculated from fluxes provided less accurate estimates of λ E compared to the measured λ E, than the use of effective aerodynamic resistances aggregated from soil and plant resistances. The results reported in this paper show that the best way of aggregating soil and plant resistances depend on the type of resistance, and the type of vegetation in the patch.

scholarly journals Sensitivity of continental United States atmospheric budgets of oxidized and reduced nitrogen to dry deposition parametrizations

2013 ◽  
Vol 368 (1621) ◽  
pp. 20130124 ◽  
Author(s):  
Robin L. Dennis ◽  
Donna B. Schwede ◽  
Jesse O. Bash ◽  
Jon E. Pleim ◽  
John T. Walker ◽  
...  
Keyword(s):  
Dry Deposition ◽  
Aerodynamic Resistance ◽  
Grid Cell ◽  
Surface Fluxes ◽  
Air Quality Model ◽  
Quality Model ◽  
Surface Exchange ◽  
Uncertainty Estimates ◽  
Regional Air Quality ◽  
Cell Changes

Reactive nitrogen (N r ) is removed by surface fluxes (air–surface exchange) and wet deposition. The chemistry and physics of the atmosphere result in a complicated system in which competing chemical sources and sinks exist and impact that removal. Therefore, uncertainties are best examined with complete regional chemical transport models that simulate these feedbacks. We analysed several uncertainties in regional air quality model resistance analogue representations of air–surface exchange for unidirectional and bi-directional fluxes and their effect on the continental N r budget. Model sensitivity tests of key parameters in dry deposition formulations showed that uncertainty estimates of continental total nitrogen deposition are surprisingly small, 5 per cent or less, owing to feedbacks in the chemistry and rebalancing among removal pathways. The largest uncertainties (5%) occur with the change from a unidirectional to a bi-directional NH 3 formulation followed by uncertainties in bi-directional compensation points (1–4%) and unidirectional aerodynamic resistance (2%). Uncertainties have a greater effect at the local scale. Between unidirectional and bi-directional formulations, single grid cell changes can be up to 50 per cent, whereas 84 per cent of the cells have changes less than 30 per cent. For uncertainties within either formulation, single grid cell change can be up to 20 per cent, but for 90 per cent of the cells changes are less than 10 per cent.

scholarly journals Significant Decrease of Uncertainties in Sensible Heat Flux Simulation Using Temporally Variable Aerodynamic Roughness in Two Typical Forest Ecosystems of China

2012 ◽  
Vol 51 (6) ◽  
pp. 1099-1110 ◽  
Author(s):  
Yanlian Zhou ◽  
Weimin Ju ◽  
Xiaomin Sun ◽  
Xuefa Wen ◽  
Dexin Guan
Keyword(s):  
Heat Flux ◽  
Roughness Length ◽  
Aerodynamic Resistance ◽  
Sensible Heat Flux ◽  
Surface Fluxes ◽  
Sensible Heat ◽  
Atmospheric Stratification ◽  
Thermal Roughness Length ◽  
Aerodynamic Roughness ◽  
Simulation Errors

AbstractAerodynamic roughness length zom is an important parameter for reliably simulating surface fluxes. It varies with wind speed, atmospheric stratification, terrain, and other factors. However, it is usually considered a constant. It is known that uncertainties in zom result in latent heat flux (LE) simulation errors, since zom links LE with aerodynamic resistance. The effects of zom on sensible heat flux (SH) simulation are usually neglected because there is no direct link between the two. By comparing SH simulations with three types of zom inputs, it is found that allowing zom temporal variation in an SH simulation model significantly improves agreement between simulated and measured SH and also decreases the sensitivity of the SH model to the heat transfer coefficient Ct, which in turn determines the linkage between zom and thermal roughness length zoh.

Effect of aerodynamic resistance modelling on SiSPAT-RS simulated surface fluxes

Agronomie ◽  
2002 ◽  
Vol 22 (6) ◽  
pp. 641-650 ◽  
Author(s):  
Jérôme Demarty ◽  
Catherine Ottlé ◽  
Christophe François ◽  
Isabelle Braud ◽  
Jean-Pierre Frangi
Keyword(s):  
Aerodynamic Resistance ◽  
Surface Fluxes ◽  
Simulated Surface

scholarly journals Re. I. Understanding galaxy sizes, associated luminosity densities, and the artificial division of the early-type galaxy population

2019 ◽  
Vol 36 ◽  
Author(s):  
Alister W. Graham
Keyword(s):  
Galaxy Formation ◽  
Surface Brightness ◽  
Early Type ◽  
Effective Parameters ◽  
Effective Surface ◽  
Dynamical Mass ◽  
Massive Galaxies ◽  
False Dichotomy ◽  
Galaxy Population ◽  
Black Hole Masses

AbstractFor decades, the deceptive simplicity of the radius $R_{\rm e}$ , enclosing an arbitrary 50% of a galaxy’s light, has hamstrung the understanding of early-type galaxies (ETGs). Half a century ago, using these ‘effective half-light’ radii from de Vaucouleurs’ $R^{1/4}$ model, Sérsic reported that bright ETGs follow the relation $\mathfrak{M}_B\propto2.5\log R_{\rm e}$ ; and consequently, one has that $\langle\mu\rangle_{\rm e}\propto2.5\log R_{\rm e}$ and $\mu_{\rm e}\propto2.5\log R_{\rm e}$ , where $\mu_{\rm e}$ and $\langle\mu\rangle_{\rm e}$ are the effective surface brightness at $R_{\rm e}$ and the mean effective surface brightness within $R_{\rm e}$ , respectively. Sérsic additionally observed an apparent transition which led him to advocate for a division between what he called dwarf and giant ETGs; a belief frequently restated to occur at $\mathfrak{M}_B \approx -18$ mag or $n\approx 2.5$ . Here, the location of this false dichotomy in diagrams using ‘effective’ parameters is shown to change by more than 3 mag simply depending on the arbitrary percentage of light used to quantify a galaxy’s size. A range of alternative radii are explored, including where the projected intensity has dropped by a fixed percentage plus a battery of internal radii, further revealing that the transition at $\mathfrak{M}_B \approx -18$ mag is artificial and does not demark a boundary between different physical processes operating on the ETG population.The above understanding surrounding the effective radius $R_{\rm e}$ is of further importance because quantities such as dynamical mass $\sigma^2R/G$ , gravitational-binding energy $GM^2/R$ , acceleration $GM/R^2$ , and the ‘Fundamental Plane’ also depend on the arbitrary percentage of light used to define R, with implications for dark matter estimates, galaxy formation theories, compact massive galaxies, studies of peculiar velocity flows, and more. Finally, some of the vast literature which has advocated for segregating the ETG population at $\mathfrak{M}_B \approx -18$ mag ( $M\approx1$ – $2\times10^{10}\,{\rm M}_{\odot}$ ) is addressed, and it is revealed how this pervasive mindset has spilled over to influence both the classical bulge versus pseudobulge debate and recently also correlations involving supermassive black hole masses.

scholarly journals Explicit Representation of Spatial Subgrid-Scale Heterogeneity in an ESM

2016 ◽  
Vol 17 (5) ◽  
pp. 1357-1371 ◽  
Author(s):  
Philipp de Vrese ◽  
Stefan Hagemann
Keyword(s):  
Land Surface ◽  
Large Fraction ◽  
Atmospheric Model ◽  
Surface Fluxes ◽  
Earth System ◽  
Subgrid Scale ◽  
Effective Parameters ◽  
Max Planck ◽  
Near Surface ◽  
Horizontal Length

Abstract In present-day Earth system models, the coupling of land surface and atmosphere is based on simplistic assumptions. Often the heterogeneous land surface is represented by a set of effective parameters valid for an entire model grid box. Other models assume that the surface fluxes become horizontally homogeneous at the lowest atmospheric model level. For heterogeneity above a certain horizontal length scale this is not the case, resulting in spatial subgrid-scale variability in the fluxes and in the state of the atmosphere. The Max Planck Institute for Meteorology’s Earth System Model is used with three different coupling schemes to assess the importance of the representation of spatial heterogeneity at the land surface as well as within the atmosphere. Simulations show that the land surface–atmosphere coupling distinctly influences the simulated near-surface processes with respect to different land-cover types. The representation of heterogeneity also has a distinct impact on the simulated gridbox mean state and fluxes in a large fraction of land surface.

scholarly journals Evaluating parameterizations of aerodynamic resistance to heat transfer using field measurements

2007 ◽  
Vol 11 (2) ◽  
pp. 769-783 ◽  
Author(s):  
Shaomin Liu ◽  
L. Lu ◽  
D. Mao ◽  
L. Jia
Keyword(s):  
Heat Transfer ◽  
Roughness Length ◽  
Aerodynamic Resistance ◽  
Soil Surface ◽  
Bare Soil ◽  
Surface Fluxes ◽  
Eddy Correlation ◽  
Correlation System ◽  
Resistance To Heat ◽  
Roughness Length For Heat

Abstract. Parameterizations of aerodynamic resistance to heat and water transfer have a significant impact on the accuracy of models of land – atmosphere interactions and of estimated surface fluxes using spectro-radiometric data collected from aircrafts and satellites. We have used measurements from an eddy correlation system to derive the aerodynamic resistance to heat transfer over a bare soil surface as well as over a maize canopy. Diurnal variations of aerodynamic resistance have been analyzed. The results showed that the diurnal variation of aerodynamic resistance during daytime (07:00 h–18:00 h) was significant for both the bare soil surface and the maize canopy although the range of variation was limited. Based on the measurements made by the eddy correlation system, a comprehensive evaluation of eight popularly used parameterization schemes of aerodynamic resistance was carried out. The roughness length for heat transfer is a crucial parameter in the estimation of aerodynamic resistance to heat transfer and can neither be taken as a constant nor be neglected. Comparing with the measurements, the parameterizations by Choudhury et al. (1986), Viney (1991), Yang et al. (2001) and the modified forms of Verma et al. (1976) and Mahrt and Ek (1984) by inclusion of roughness length for heat transfer gave good agreements with the measurements, while the parameterizations by Hatfield et al. (1983) and Xie (1988) showed larger errors even though the roughness length for heat transfer has been taken into account.

Modelling the transpiration of a greenhouse zucchini crop grown under a Mediterranean climate using the Penman-Monteith equation and its simplified version

2004 ◽  
Vol 55 (9) ◽  
pp. 931 ◽  
Author(s):  
Youssef Rouphael ◽  
Giuseppe Colla
Keyword(s):  
Solar Radiation ◽  
Vapour Pressure ◽  
Irrigation Management ◽  
Central Italy ◽  
Aerodynamic Resistance ◽  
Gravimetric Method ◽  
Vapour Pressure Deficit ◽  
Stomatal Resistance ◽  
Coefficient Of Determination ◽  
Monteith Equation

In Mediterranean climates, high temperatures and vapour pressure deficits are currently observed in greenhouses during summer. These conditions are responsible for a high transpiration rate leading to greater water consumption. Measuring and modelling transpiration can be useful for efficient irrigation management by allowing prediction of short-term water demand. The rate of transpiration of zucchini crops (Cucurbita pepo L.) grown in soilless culture was measured in a greenhouse located at Viterbo, central Italy, during spring–summer 2002. The Penman-Monteith equation was used to predict the potential transpiration of the plants averaged over 30-min intervals using different approaches in the calculation of aerodynamic resistance. The values obtained were compared with transpiration measured by a gravimetric method by weighing plants on an electronic balance. Leaf temperature was lower (up to 5°C) than air temperature on clear summer days owing to high transpiration rates. Stomatal resistance was computed and found to be exponentially related to solar radiation. The best fit in transpiration between the Penman-Monteith calculated and those measured was achieved when the heat transfer in the former was obtained as a process of mixed convection, where the slope of the regression was 1, and there was improvement of the coefficient of determination (R2 = 0.96). A simplified model of daytime transpiration based on easily measured variables (solar radiation and vapour pressure deficit) was developed and produced strong agreement with the gravimetric method (R2 = 0.93).

scholarly journals Modelling plant transpiration and leaf climate using CFD

2021 ◽  
Vol 2116 (1) ◽  
pp. 012076
Author(s):  
Wito Plas ◽  
Michel De Paepe
Keyword(s):  
Water Vapour ◽  
Food Production ◽  
Aerodynamic Resistance ◽  
Stomatal Resistance ◽  
Sustainable Food ◽  
Water Vapour Flux ◽  
Water Vapour Transport ◽  
In Series ◽  
Vapour Flux ◽  
Growing Conditions

Abstract Research into vertical farms or plant factories is steadily increasing over the years, as the demand for sustainable food production and a shift to more environmental friendly food production is occurring. Modelling plant climate in these confined spaces is therefore essential to guarantee optimal growing conditions. Modelling of plant climate has already been done in greenhouses, but at length scales much bigger than individual leaves. In this study, one single plant will be modelled, using computational fluid dynamics and by incorporating additional source terms in the relevant transport equations. Plants are modelled using the big leaf approach, where a plant is modelled as one artificial leaf. Water vapour flux in plants is controlled by two resistances in series, the aerodynamic resistance, which is a function of the boundary layer around the leaves and the stomatal resistance, which is the resistance against water vapour transport in leaves. Two different plants are studied, impatiens pot plant and basil plants. Values of stomatal resistance for these crops are obtained from literature or were measured. Evapotranspiration was compared with the Penman-Monteith equation.

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