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1.
Aerodynamic and canopy resistance of short-rotation forest in relation to leaf area index and climate 总被引：3，自引：0，他引：3
Anders Lindroth 《Boundary-Layer Meteorology》1993,66(3):265-279
The aerodynamic and canopy resistances of a willow short-rotation stand were estimated during the course of a growing season on the basis of micrometeorological measurements. The normalized roughness length (z
0/h) decreased from about 0.10 at a leaf area index of one to 0.05 at a leaf area index of seven. This implies that the aerodynamic resistance at peak leaf area index is more than twice the value at zero leaf area index, all other variables unchanged. The canopy resistance depended strongly on air water concentration deficit and on leaf area index. The Lohammar equation showed good agreement between estimated and measured canopy resistances over the whole course of leaf development. The stand was well-coupled to the atmosphere only for very small values of leaf area indices, less than one, and it was practically de-coupled for leaf area indices above two. From the point of view of factors controlling evaporation, this type of stand acts as a traditional forest at the beginning and end of the season and as an agricultural crop in the middle of the season. 相似文献
2.
Synchronous sonic anemometric measurements at five heightswithin a mixed coniferous forest were used to test two different parameterisations ofcanopy architecture in the application of a second-order turbulence closure model. Inthe computation of the leaf drag area, the aerodynamic sheltering was replaced with anarchitectural sheltering, assumed to be analogous to the clumping index defined in radiativetransfer theory. Consequently, the ratio of leaf area density and sheltering factor was approximatedby the effective leaf area or the mean contact number, both obtained from the inversion of non-destructive optical measurements. The first parameter represents the equivalentrandomly dispersed leaf area in terms of shading, the second is the average number of leavesthat a straight line intercepts penetrating the canopy with a certain zenith angle. Theselection of this direction was determined by the analysis of the mean angle of the wind vectorduring sweep events. The drag coefficient values obtained from the inversion of themomentum flux equation, using the two proposed parameterisations, are in good agreement withvalues found in the literature. The predicted profiles of turbulence statistics reasonablymatch actual measurements, especially in the case of the mean contact numberparameterisation. The vertical profile of leaf drag area, obtained by forcing the turbulence modelto match the observed standard deviation of vertical velocity (w), is intermediatebetween the two empirical ones. Finally, the proposed canopy parameterisations were appliedto a Lagrangian transport model to predict vertical profiles of air temperature, H2O andCO2 concentration. 相似文献
3.
G. Rana N. Katerji M. Mastrorilli M. El Moujabber 《Theoretical and Applied Climatology》1994,50(1-2):61-71
Summary A simple method for estimating actual evapotranspiration (ET) could become a suitable tool for irrigation scheduling. Resistance models can be useful if data on canopy resistance to water vapor flow (rc) and on aerodynamic resistance (ra) are available. These parameters are complex and hard to obtain. In this studyrc is analysed for a reference crop (grass meadow). Canopy resistance is dependent on climate, weather (radiation, atmospheric vapor pressure deficit, aerodynamic resistance), agronomic practices (irrigation, grass cutting) and time scale (hour, day). Anrc model, proposed by Katerji and Perrier (KP model), using some meteorological parameters as inputs, is presented. Canopy resistance calculated according to the KP model was used to estimate a referenceET
ref on hourly and daily time scales.TheET
ref estimated using the KP model on a daily time scale was compared with a model proposed by Allen, Jensen, Wright and Burman (AJWB model) — in whichrc depends on leaf area index only — and with direct measurements from a weighing lysimeter. The results show an underestimation of 18% for the AJWB model against an underestimation of 2% for the KP model. Since the hypotheses are the same for both models and aerodynamic resistance plays a secondary role, the better results obtained by the KP model are due torc modelling.With 11 Figures 相似文献
4.
Jean-Paul Lhomme Nader Katerji Alain Perrier Jean-Michel Bertolini 《Boundary-Layer Meteorology》1988,43(4):383-392
The analysis presented in this paper aims at a better understanding of the potential role of radiative temperature, as measured by a radiometer over crops, in sensible heat flux calculation. Defining radiative temperature as the mean temperature of the surfaces viewed by the radiometer (leaves and soil surface) and assuming that an Ohm's law type formula can be used to express sensible heat flux as a function of the difference between air temperature and radiative temperature, the aerodynamic resistance which divides this temperature difference has been analytically defined. The parameters which appear in the resistance expression depend essentially on wind velocity and canopy structure but also on the inclination angle of the radiometer. Finally an experimental verification is presented with data obtained over a potato crop. 相似文献
5.
Continuous measurement of aerodynamic and alfalfa canopy resistances using the Bowen ratio-energy balance and Penman-Monteith methods 总被引：5，自引：0，他引：5
To investigate the alfalfa crop response to environmental factors, a Bowen ratio-energy balance method was used to evaluate short-term alfalfa canopy resistance. Continuous evapotranspiration (ET
a
) and the aerodynamic resistance (r
a
) for an alfalfa crop in each 20-min interval were calculated. Using the calculated ET
a
and r
a
and the Penman-Monteith approach, the bulk stomatal or actual canopy resistance (r
c
) was evaluated. The continuous 20-min resistances were computed for clear and partially cloudy sky conditions, and different average crop heights. The results show that this technique can satisfactorily be used to study the manner in which the aerodynamic and canopy resistances respond to short-term variations in weather elements such as photosynthetically active radiation (PAR), wind speed and atmospheric saturation vapor deficit.Research Assistant Professor and Assistant Utah State Climatologist, Research Associate Professor and Research Assistant, respectively. 相似文献
6.
The conductance of a maize crop and the underlying soil to ozone under various environmental conditions 总被引：2，自引：0，他引：2
Flux measurements of ozone and water vapour employing the eddy correlation technique were used to determine the surface conductance and canopy conductance to ozone. In the surface conductance to ozone, all surfaces at which ozone is destroyed and the transport process to these surfaces are included. The canopy conductance to ozone represents the ozone uptake of transpiring plant parts. The surface conductance to ozone of the maize crop and the underlying soil was generally larger than the canopy conductance to ozone. This means that beside the uptake by stomata, there was another important ozone sink. Under wet soil surface conditions, the surface conductance and the canopy conductance to ozone coincided. This indicates that the resistance of wet soil and the remaining plant parts (cuticle) to ozone was much larger than the stomatal or soil resistance. On the other hand, under dry soil conditions the conductances differ, largely caused by a variation in the transport process to the soil. The transport of ozone to soil increased with increasing friction velocity (u
*) and decreased with increasing atmospheric stability, leaf area index (LAI) or crop height (h). These effects for midday (unstable) conditions were parameterized with an in-crop aerodynamic resistance,r
inc in a very straightforward way;r
inc=13.9 LAIh/u
*+67 (cc.=0.77). If the ozone flux in air pollution models is described with a simple resistance model (Big Leaf model), the extra destruction at the soil should be modelled using an in-crop aerodynamic resistance. For these measurements the ozone flux to the soil was 0–65% of the total ozone flux measured above the crop. Under wet soil conditions, this was less than 20%; under dry soil conditions, this was 30–65%. 相似文献
7.
We analyse single-point velocity statistics obtained in a wind tunnel within and above a model of a waving wheat crop, consisting of nylon stalks 47 mm high and 0.25 mm wide in a square array with frontal area index 0.47. The variability of turbulence measurements in the wind tunnel is illustrated by using a set of 71 vertical traverses made in different locations, all in the horizontally-homogeneous (above-canopy) part of the boundary layer. Ensemble-averaged profiles of the statistical moments up to the fourth order and profiles of Eulerian length scales are presented and discussed. They are consistent with other similar experiments and reveal the existence of large-scale turbulent coherent structures in the flow. The drag coefficient in this canopy as well as in other reported experiments is shown to exhibit a characteristic height-dependency, for which we propose an interpretation. The velocity spectra are analysed in detail; within and just above the canopy, a scaling based on fixed length and velocity scales (canopy height and mean horizontal wind speed at canopy top) is proposed. Examination of the turbulent kinetic energy and shear stress budgets confirms the role of turbulent transport in the region around the canopy top, and indicates that pressure transport may be significant in both cases. The results obtained here show that near the top of the canopy, the turbulence properties are more reminiscent of a plane mixing layer than a wall boundary layer. 相似文献
8.
降水资源是农作物的主要水分来源,农作物通过吸收土壤中的水分维持正常的生长发育,但由于未考虑农作物冠层对降水截留作用,在水资源评估和农田水分平衡研究中往往高估降水作用。该文通过2018年玉米生长季在辽宁锦州农业气象试验站开展的降水模拟试验系统分析了玉米冠层对降水的截留效应,结果表明:在降水量一定条件下,玉米冠层截留量与叶面积指数的二次多项式拟合相关最佳;在叶面积指数一定条件下,玉米冠层截留量与降水量的幂函数拟合相关最佳。综合叶面积指数和降水量分析表明:玉米冠层截留量与叶面积指数平方及降水量对数函数拟合呈正相关。根据我国玉米传统种植方式,高产玉米的叶面积指数最大一般为5~6,因此,对一次降水的最大截留量通常约为1.5~2.3 mm,当叶面积指数小于1时,对降水的截留可忽略不计。 相似文献
9.
William P. Kustas Martha C. Anderson John M. Norman Fuqin Li 《Boundary-Layer Meteorology》2007,122(1):167-187
In many land-surface models using bulk transfer (one-source) approaches, the application of radiometric surface temperature
observations in energy flux computations has given mixed results. This is due in part to the non-unique relationship between
the so-called aerodynamic temperature, which relates to the efficiency of heat exchange between the land surface and overlying
atmosphere, and a surface temperature measurement from a thermal-infrared radiometer, which largely corresponds to a weighted
soil and canopy temperature as a function of radiometer viewing angle. A number of studies over the past several years using
multi-source canopy models and/or experimental data have developed simplified methods to accommodate radiometric–aerodynamic
temperature differences in one-source approaches. A recent investigation related the variability in the radiometric–aerodynamic
relation to solar radiation using experimental data from a variety of landscapes, while another used a multi-source canopy
model combined with measurements over a wide range in vegetation density to derive a relationship based on leaf area index.
In this study, simulations by a detailed multi-source soil–plant–environment model, Cupid, which considers both radiative
and turbulent exchanges across the soil–canopy–air interface, are used to explore the radiometric–aerodynamic temperature
relations for a semi-arid shrubland ecosystem under a range of leaf area/canopy cover, soil moisture and meteorological conditions.
The simulated radiometric-aerodynamic temperatures indicate that, while solar radiation and leaf area both strongly affect
the magnitude of this temperature difference, the relationships are non-unique, having significant variability depending on
local conditions. These simulations also show that soil–canopy temperature differences are highly correlated with variations
in the radiometric–aerodynamic temperature differences, with the slope being primarily a function of leaf area. This result
suggests that two-source schemes with reliable estimates of component soil and canopy temperatures and associated resistances
may be better able to accommodate variability in the radiometric–aerodynamic relation for a wider range in vegetated canopy
cover conditions than is possible with one-source schemes. However, comparisons of sensible heat flux estimates with Cupid
using a simplified two-source model and a one-source model accommodating variability in the radiometric-aerodynamic relation
based on vegetation density gave similar scatter. On the other hand, with experimental data from the shrubland site, the two-source
model generally outperformed the one-source scheme. Clearly, vegetation density/leaf area has a major effect on the radiometric–aerodynamic
temperature relation and must be considered in either one-source or two-source formulations. Hence these adjusted one-source
models require similar inputs as in two-source approaches, but provide as output only bulk heat fluxes; this is not as useful
for monitoring vegetation conditions. 相似文献
10.
The effect of uncertainty in aerodynamic resistance on evaporation estimates from the combination model 总被引：1，自引：0，他引：1
Evaporation estimates from a soybean crop calculated from the combination model are insensitive to aerodynamic resistance. The insensitivity arises from a strong link between evaporation and the vapour pressure deficit of the air and bulk stomatal resistance. The sensitivity of aerodynamic resistance to errors in surface roughness and zero-plane displacement is considered. The resistance is found to be more sensitive to errors in surface roughness than to errors in zero-plane displacement. However, large errors in these have little effect on calculated evaporation. Both surface roughness and zero-plane displacement are empirically related to crop height and leaf area index. Errors incurred by ignoring bluff-body effects and atmospheric stability are small in estimating both resistance and evaporation. Evaporation can be calculated adequately from empirical estimates of surface roughness and zero-plane displacement and single-level measurements of windspeed. 相似文献
11.
Qin Wenhan 《Acta Meteorologica Sinica》1995,9(1):78-86
Using data on leaf area density and wind profiles above and within canopies of wheat,rice,soybean and corn,thecenter-of-pressure method (CPM),originally proposed by Thom (1971),is first validated in the field.Aphysically-based model for directly calculating zero-displacement height (d) is derived.The comparison between thefriction velocity (u_*) estimated with CPM and that with eddy correlation technique shows that CPM not only works wellin the field,but also produces more steady and accurate estimates of aerodynamic parameters (which are hardly affectedby atmospheric thermal stability),than those with the widely-used log-profile fitting method in diabatic atmosphere.The results presented in this paper also demonstrate that the ratios of d,z_0 to crop height h usually vary with canopy ar-chitecture,atmospheric stratification and turbulent exchange intensity,and are not just constants as commonly assumedor used.d/h raises with an increase of relative height of the maximum foliage layer and wind extinction coefficientwithin the canopy.Only for crops with short stem and moderate foliage density,can the relations d= 0.64h,z_0=0.08hkeep stable.In addition,for long stem crops or sparse canopies,the fairly large shear stress at the soil surface and the va-riation of the exponent in the relationship between drag coefficient and wind speed undoubtedly influence the accuracyof CPM to a certain extent. 相似文献
12.
13.
A Simple Model for Spatially-averaged Wind Profiles Within and Above an Urban Canopy 总被引：2，自引：2，他引：0
This paper deals with the modelling of the flow in the urban canopy layer. It critically reviews a well-known formula for
the spatially-averaged wind profile, originally proposed by Cionco in 1965, and provides a new interpretation for it. This
opens up a number of new applications for modelling mean wind flow over the neighbourhood scale. The model is based on a balance
equation between the obstacle drag force and the local shear stress as proposed by Cionco for a vegetative canopy. The buildings
within the canopy are represented as a canopy element drag formulated in terms of morphological parameters such as λ
f
and λ
p
(the ratios of plan area and frontal area of buildings to the lot area). These parameters can be obtained from the analysis
of urban digital elevation models. The shear stress is parameterised using a mixing length approach. Spatially-averaged velocity
profiles for different values of building packing density corresponding to different flow regimes are obtained and analysed.
The computed solutions are compared with published data from wind-tunnel and water-tunnel experiments over arrays of cubes.
The model is used to estimate the spatially-averaged velocity profile within and above neighbourhood areas of real cities
by using vertical profiles of λ
f
. 相似文献
14.
Summary The dependence of the albedo on illumination direction is analyzed by constructing a canopy model in which the individual leaves are planar, Lambertian reflectors. Leaf transmission is treated separately, and is assumed to be proportional to the cosine of the zenith angle of the leaf normal. Effects of shading and obscuration are formulated assuming random distribution of the leaves with respect to the viewing and illumination directions. Variants of the model with different azimuthal leaf distributions are created and discussed as explicit expressions of the viewing/illumination geometry and the canopy characteristics.The canopy spectral single-scattering albedo factors, which are the conditional probabilities of a photon escaping from the canopy after a first reflection or a first transmission, are obtained by numerical integration over a hemisphere of the bidirectional reflectance and transmittance factors. Our analysis identifies the ratio of the projection of leaf area on the vertical plane perpendicular to the principal plane to that on a horizontal plane as the parameter that controls the dependence of the albedo on the solar zenith angle. The albedo factor due to the leaf transmittance generally increases with the zenith angle of illuminating beam more sharply than that due to the leaf reflectance.Model variants with various azimuthal distributions are compared with measured albedo of soybeans. Second and higher order scatterings are accounted for in a simplified way. The degree to which a model variant fits the measured albedo and its change with the solar zenith angle depends both on the leaf inclination angleand the azimuthal distribution of the leaf area.With 6 Figures 相似文献
15.
The deposition velocity (V
d) of nitric acid vapor over a fully leafed deciduous forest was estimated using flux/gradient theory. HNO3 deposition velocities ranged from 2.2 to 6.0cm/s with a mean V
don the order of 4.0cms-1. Estimates of V
dfrom a detailed canopy turbulence model gave deposition velocities of similar magnitude. The model was used to investigate the sensitivity of V
dto the leaf boundary-layer resistance and leaf area index (LAI). Although modeled deposition velocities were found to be sensitive to the parameterization of the leaf boundary-layer resistance, they were less sensitive to the LAI. Modeled V
d's were found to peak at LAI = 7. 相似文献
16.
Water-flume experiments are conducted to study the structure of turbulent flow within and above a sparse model canopy consisting
of two rigid canopies of different heights. This difference in height specifies a two-dimensional step change from a rough
to a rougher surface, as opposed to a smooth-to-rough transition. Despite the fact that the flow is in transition from a rough
to a rougher surface, the thickness of the internal boundary layer scales as x
4/5, consistent with smooth-to-rough boundary layer adjustment studies, where x is the downstream distance from the step change. However, the analogy with smooth-to-rough transitions no longer holds when
the flow inside the canopy and near the canopy top is considered. Results show that the step change in surface roughness significantly
increases turbulence intensities and shear stress. In particular, there is an adjustment of the mean horizontal velocity and
shear stress as the flow passes over the rougher canopy, so that their vertical profiles adjust to give maximum values at
the top of this canopy. We also observe that the magnitude and shape of the inflection in the mean horizontal velocity profile
is significantly affected by the transition. The horizontal and vertical turbulence spectra compare well with Kolmogorov’s
theory, although a small deviation at high frequencies is observed in the horizontal spectrum within the canopy. Here, for
relatively low leaf area index, shear is found to be a more effective mechanism for momentum transfer through the canopy structure
than vortex shedding. 相似文献
17.
A model for predicting actual evapotranspiration under soil water stress in a Mediterranean region 总被引：1，自引：0，他引：1
G. Rana N. Katerji M. Mastrorilli M. El Moujabber 《Theoretical and Applied Climatology》1997,56(1-2):45-55
Summary In this paper a model for estimating actual evapotranspiration is developed and tested for field crops (grain sorghum and sunflower) maintained under water stress conditions. The model is based on the Penman-Monteith formulation of ET in which canopy resistance (r
c) is modeled with respect to the crop water status and local climatological conditions. The model was previously tested on reference grass; in this last case no reference was made to soil water conditions andr
c was modeled only as a function of climatological parameters. Herer
c is expressed as a function of available energy, vapour pressure deficit, aerodynamic resistance and crop water status by means of predawn leaf water potential. Results, obtained with various crop water stress intensities, show that, on a daily scale, calculated ET is 98% and 95% of the measured ET for sorghum and sunflower respectively. The correlation between daily calculated and measured ET is very high (r
2 = 0.95 for sorghum andr
2 = 0.98 for sunflower). On an hourly scale, the model works very well when the crops were not stressed and during the senescence stage. In case of weak and strong stress the model has to be used with some precautions.With 9 Figures 相似文献
18.
利用建立的一方程模式对植被气象场和湍流场进行了模拟计算。结果表明：在植被叶面积密度最大值处，由植被叶面积产生的阻力使风速急剧减小，而后平缓接近地面风速值。Reynolds应力从植被顶部向下剧烈减小，在Z／Hc值为0．4～0．6之间衰减迅速；冠层下部风速小且切变弱，湍流未能充分发展，因而动量输送甚微。由于在植被内部环境中存在着湍流通量的辐散或辐合的现象，湍流强度从植被底部开始由下至上逐渐增强，在冠层上方则基本保持不变。 相似文献
19.
作物系数是计算作物蒸散量的关键参数。利用2006—2008年和2011年辽宁锦州玉米农田生态系统的涡度相关、气象、作物发育期及叶面积指数观测数据,分析不受水分胁迫条件下玉米逐日作物系数特征及其与叶面积指数的关系。研究表明:作物系数与玉米农田实际蒸散均呈单峰型变化,约在7月末至8月初达到最大值 (玉米开花吐丝期)。在此基础上,建立了不受水分胁迫条件下玉米逐日作物系数与叶面积指数关系 (达到0.01显著性水平), 同时,采用积温表示的标准化生育期方法模拟相对叶面积指数,并建立了逐日作物系数与相对叶面积指数关系 (达到0.01显著性水平),解决了无叶面积观测地区玉米逐日实际蒸散量的计算。研究结果可为玉米农田用水管理以及灌溉措施的制定提供参考。 相似文献
20.
A simple mathematical model is proposed, which combines the effects of mean wind speed, plant spacing and the drag coefficients of individual plants to calculate the fluctuating airflow within a waving crop canopy. The model is non-linear and is only amenable to analytical treatment when linearized; however, the full non-linear version can be solved on an analogue computer.The linear and non-linear results show unexpectedly good agreement, and the success of the linearization allows clear conclusions to be drawn about the relationship between the elasticity, geometry and mean wind speed through a stand of plants and the fluctuating components of airflow and stalk motion.Finally, the analytical results are in qualitative agreement with wind-tunnel results from two model canopies with different characteristics. 相似文献