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1.
Summary This paper presents a study of the sensibility of the Penman-Monteith evapotranspiration model to climatic (available energy and vapour pressure deficit) and parametric (aerodynamic and canopy resistances, r a and r c respectively) factors in a semi-arid climate, for crops in contrasting water status (well irrigated and under water stress) and of different heights. Three experiments were carried out in southern Italy on reference grass (≈ 0.1 m), grain sorghum (≈ 1 m) and sweet sorghum (≈ 3 m). For this analysis the sensitivity coefficients, taken as hourly means, were evaluated during the growth season when the crops completely covered the soil. The relative errors on evapotranspiration were also evaluated for r a and r c . The results showed that, for reference grass, available energy and aerodynamic resistance play a major role. For crops under water stress the most important term to evaluate is canopy resistance. For a tall crop, as sweet sorghum, the role of the vapour pressure deficit is fundamental, both when the crop is in good water status and under water stress. Received July 14, 1997 Revised February 5, 1998  相似文献   

2.
Evapotranspiration and canopy resistance of grass in a Mediterranean region   总被引：1，自引：3，他引：1  
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   

3.
Summary The evaporation of deep crops such as forests is usually considered in terms of the two-resistance Penman-Monteith model, though this conflates two of the three resistances actually involved, i.e. the canopy resistancer c between the transpiring leaves and the top of the canopy, and the resistancer s due to the stomates of the leaves. A review of the literature on these and the aerodynamic resistancer a (between the crop and the atmosphere) shows how distinctly different they are, and therefore how inappropriate it is to lump any two together.Once the soil has dried substantially,r s depends approximately onM –2, whereM is the fractional available soil moisture.As regards grassed surfaces,r a is 300/u s m–1, whereu is the wind speed at 2 m.With 2 Figures  相似文献   

4.
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   

5.
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   

6.
In unstable conditions, the set of equations defining the aerodynamic resistance to sensible heat transfer, r a , cannot be solved analytically. An iterative technique must be used to obtain r a exactly, but this is cumbersome and time consuming. In this paper, a new, empirical equation is presented relating the ratio, Q, of the aerodynamic resistances in neutral and unstable conditions, to the bulk Richardson number, Ri B . The equation takes the form Q = a + b(–Ri) c , where a, b and c are empirical functions of (z – d)/z om . This model is shown to predict r awith a mean absolute error of 0.06 s m–1 over the ranges -15 < Ri B < 0 and 10 < (z – d)/z om < 2300. Statistical comparison with other equations that have been proposed for r a in unstable conditions indicates the superior precision of the model presented here.  相似文献   

7.
Estimating sensible heat flux from radiometric temperature over crop canopy   总被引：3，自引：0，他引：3  
The model devised by Lhommeet al. (1988) allows one to calculate the sensible heat flux over a homogeneous crop canopy from radiometric surface temperature by adding a so-called canopy aerodynamic resistance to the classical aerodynamic resistance calculated above the canopy. This model is reformulated in order to simplify the mathematical procedure needed to calculate this additional resistance. Analytical expressions of micrometeorological profiles within the canopy are introduced. Assuming a constant leaf area density, an analytical expression of canopy aerodynamic resistance is inferred, which is a function of wind velocity, inclination angle of the radiometer and crop characteristics such as crop height, leaf area index, inclination index of the foliage and leaf width. Sensitivity of this resistance to the different parameters is investigated. The most significant are wind velocity and LAI. Finally, the predictions of the model are tested against two sets of measurements obtained for two different crops, potato and maize.  相似文献   

8.
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   

9.
Summary This paper describes a Bowen ratio/energy balance (BREB) system which, in conjunction with an infra-red gas analyzer (IRGA), is referred to as BREB+ and is used to estimate evapotranspiration (ET) and net CO2 flux (NCF) over crop canopies. The system is composed of a net radiometer, soil heat flux plates, two psychrometers based on platinum resistance thermometers (PRT), bridge circuits to measure resistances, an IRGA, air pumps and switching valves, and a data logger. The psychrometers are triple shielded and aspirated, and with aspiration also between the two inner shields. High resistance (1 000 ohm) PRT's are used for dry and wet bulbs to minimize errors due to wiring and connector resistances. A high (55 K ohm) fixed resistance serves as one arm of the resistance bridge to ensure linearity in output signals. To minimize gaps in data, to allow measurements at short (e.g., 5 min) intervals, and to simplify operation, the psychrometers were fixed at their upper and lower position over the crop and not alternated. Instead, the PRT's, connected to the bridge circuit and the data logger, were carefully calibrated together. Field tests using a common air source showed appartent effects of the local environment around each psychrometer on the temperatures measured. ET rates estimated with the BREB system were compared to those measured with large lysimeters. Daily totals agreed within 5%. There was a tendency, however, for the lysimeter measurements to lag behind the BREB measurements. Daily patterns ofNCF estimated with the BREB+ system are consistent with expectations from theories and data in the literature. Side-by-side comparisons with a stirred Mylar canopy chamber showed similarNCF patterns. On the other hand, discrepancies between the results of the two methods were quite marked in the morning or afternoon on certain dates. Part of the discrepancies may be attributed to inaccuracies in the psychrometric temperature measurements. Other possible causes include the highly artificial air turbulence in the canopy chamber and possible associated stomatal response. More work is necessary to identify conclusively the causes. In spite of these uncertainties, the BREB+ technique appears well suited for the automated and simultaneous tracking of photosynthetic performance and water economy of crops in their virtually undisturbed natural environment.To whom reprint requests should be sent.With 7 Figures  相似文献   

10.
The study compares two formulas for calculating the daily evapotranspiration ET0 for a reference crop. The first formula was proposed by Allen et al. (AL), while the second one was proposed by Katerji and Perrier with the addition of the carbon dioxide (CO2) effect on evapotranspiration (KP). The study analyses the impact of the calculation by the two formulas on the irrigation requirement (IR). Both formulas are based on the Penman-Monteith equation but adopt different approaches for parameterising the canopy resistance r c . In the AL formula, r c is assumed constant and not sensitive to climate change, whereas in the KP formula, r c is first parameterised as a function of climatic variables, then ET0 is corrected for the air CO2 concentration. The two formulas were compared in two periods. The first period involves data from two sites in the Mediterranean region within a measured climate change period (1981–2006) when all the input climatic variables were measured. The second period (2070–2100) involves data from a future climate change period at one site when the input climatic variables were forecasted for two future climate scenarios (A2 and B2). The annual cumulated values of ET0 calculated by the AL formula are systematically lower than those determined by the KP formula. The differences between the ET0 estimation with the AL and KP formulas have a strong impact on the determination of the IR for the reference crop. In fact, for the two periods, the annual values of IR when ET0 is calculated by the AL formula are systematically lower than those calculated by the KP formula. For the actual measured climate change period, this reduction varied from 26 to 28 %, while for the future climate change period, it varied based on the scenario from 16 % (A2) to 20 % (B2).  相似文献   

11.
Summary  A global warming, primarily affecting wintertime conditions at high latitudes will influence the functioning of the boreal forest. The least known term of the winter water-balance equation is evaporation of snow intercepted in forest canopies. Several investigations stress the importance of snow-interception evaporation in coniferous forests and evaporation fractions of gross precipitation as large as 0.2–0.5 have been observed by investigators in Scotland, Canada, and Japan. Evaporation rates as high as 0.56 mm h−1 are reported. The largest differences between the rain and snow interception evaporation processes are the differences in storage. Snow storage (both mass and duration) is often an order of magnitude larger than that for rain. Snow interception changes the canopy albedo although some studies indicate the opposite. Process knowledge is limited because of measurement difficulties but it is known that canopy closure, aerodynamic resistance (r a ), and vapour-pressure deficit are important factors. Existing formulations of r a as function of storage location and age cannot fully explain observed differences in evaporation rates. Operationalhydrology and weather models, and GCMs describe snow interception in a very simplified way and might benefit from incorporation of more realistic schemes. Received June 28, 1999  相似文献   

12.
In this study, weighing lysimeters were used to investigate the daily crop coefficient and evapotranspiration of wheat and maize in the Fars province, Iran. The locally calibrated Food and Agriculture Organization (FAO) Penman–Monteith equation was used to calculate the reference crop evapotranspiration (ETo). Micro-lysimetry was used to measure soil evaporation (E). Transpiration (T) was estimated by the difference between crop evapotranspiration (ETc) and E. The single crop coefficient (K c) was calculated by the ratio of ETc to ETo. Furthermore, the dual crop coefficient is composed of the soil evaporation coefficient (K e) and the basal crop coefficients (K cb) calculated from the ratio of E and T to ETo, respectively. The maximum measured evapotranspiration rate for wheat was 9.9 mm?day?1 and for maize was 10 mm?day?1. The total evaporation from the soil surface was about 30 % of the total wheat ETc and 29.8 % of total maize ETc. The single crop coefficient (K c) values for the initial, mid-, and end-season growth stages of maize were 0.48, 1.40, and 0.31 and those of wheat were 0.77, 1.35, and 0.26, respectively. The measured K c values for the initial and mid-season stages were different from the FAO recommended values. Therefore, the FAO standard equation for K c-mid was calibrated locally for wheat and maize. The K cb values for the initial, mid-, and end-season growth stages were 0.23, 1.14, and 0.13 for wheat and 0.10, 1.07, and 0.06 for maize, respectively. Furthermore, the FAO procedure for single crop coefficient showed better predictions on a daily basis, although the dual crop coefficient method was more accurate on seasonal scale.  相似文献   

13.
Aerodynamic Scaling for Estimating the Mean Height of Dense Canopies   总被引：1，自引：1，他引：0  
We used an aerodynamic method to objectively determine a representative canopy height, using standard meteorological measurements. The canopy height may change if the tree height is used to represent the actual canopy, but little work to date has focused on creating a standard for determining the representative canopy height. Here we propose the ‘aerodynamic canopy height’ h a as the most effective means of resolving the representative canopy height for all forests. We determined h a by simple linear regression between zero-plane displacement d and roughness length z 0, without the need for stand inventory data. The applicability of h a was confirmed in five different forests, including a forest with a complex canopy structure. Comparison with stand inventory data showed that h a was almost equivalent to the representative height of trees composing the crown surface if the forest had a simple structure, or to the representative height of taller trees composing the upper canopy in forests with a complex canopy structure. The linear relationship between d and z 0 was explained by assuming that the logarithmic wind profile above the canopy and the exponential wind profile within the canopy were continuous and smooth at canopy height. This was supported by observations, which showed that h a was essentially the same as the height defined by the inflection point of the vertical profile of wind speed. The applicability of h a was also verified using data from several previous studies.  相似文献   

14.
A field experiment was conducted in a maize field in 2006 in an arid area of the Yellow River Basin in China. The daytime evapotranspiration (ETc) and soil evaporation beneath the maize canopy (E g) were measured by Bowen ratio energy balance method and micro-lysimeters, respectively. The results showed that the total ETc during maize growth season was 696 mm, and the maximum values occurred at about 90–140 days after sowing. The crop coefficient (K c), which was calculated from the ratio of ETc to reference evapotranspiration (ET0), was quite different from the values reported by other researchers in similar climate areas, with average values of 0.34, 0.47, 1.0 and 0.9 for initial, development, mid-season and late-season stages, respectively. High correlations between leaf area index (LAI) and average K c for every 4 days were obtained. The total E g was 201.4 mm with average values ranged from 0.92 to 2.05 for four growth stages of maize; and accounted for around 28.9 % of ETc. The ratio E g/ETc showed high negative relationship with LAI. These results were very important in precise management of irrigation for maize in Yellow River Basin areas.  相似文献   

15.
Summary ?The performance of the Penman-Monteith (PM) equation to estimate daily reference evapotranspiration (ETO) was investigated by attributing three distinct features to the canopy resistance (r c): (i) r c constant at 70 s m−1 (Allen et al., 1998; FAO Irrigation and Drainage Paper n. 56), (ii) r c variable as linear function of a critical resistance r c, depending on weather variables and empirical parameters relating r c to r * (Katerji and Perrier, 1983; Agronomie, 3[6]: 513–521) and (iii) r c variable as a mechanistic function of weather variables only (Todorovic, 1999; J. Irrig. Drainage Eng., ASCE, 125[5]: 235–245). Daily weather and grass lysimeter data, measured for a period of seven years at Policoro (Southern Italy), were used. The results confirmed the relative robustness of the PM method with constant r c while better estimates were obtained only when variable r c was used. The mechanistic approach of Todorovic (1999) provided the best estimates, while the approach of Katerji and Perrier (1983), with empirically derived parameters, has shown to be not conservative enough to be extended to different locations without calibration. Received January 2, 2002; revised October 31, 2002; accepted December 7, 2002  相似文献   

16.
Eddy fluxes of CO2, water vapor,and sensible heat over a deciduous forest   总被引：12，自引：0，他引：12  
Fluxes of CO2, latent heat and sensible heat were measured above a fully-leafed deciduous forest in eastern Tennessee with the eddy correlation technique. These are among the first reported observations over such a surface. The influences of solar radiation, vapor pressure deficit and the aerodynamic and canopy resistances on these mass and energy exchanges are examined. Following a concept introduced by McNaughton and Jarvis (1983), examination of our data suggest that the water vapor exchange of a deciduous forest is not as strongly coupled with net radiation as is that of agricultural crops. The degree of decoupling is smaller than in the case of a coniferous forest. This difference may be attributable in part to the greater aerodynamic resistance to water vapor transfer in a deciduous forest. It appears that the concept of decoupling may be extended to the CO2 exchange of a deciduous forest as well.Published as Paper No. 7832, Journal Series, Nebraska Agricultural Research Division. ATDD Contribution No. 85-17.  相似文献   

17.
The energy balance was measured for the dry canopy of narrow-leaved snow tussock (Chionochloa rigida), and measurements of transpiration were obtained from a large weighing lysimeter.Typical maximum summer transpiration rates of 0.21–0.43 mmhr-1 (140–290 W m-2) were recorded. The latent heat flux accounted for less than 40% of net radiation. The estimated value of the bulk stomatal resistance (r ST) for 29 days was 158 s m-1, and the decoupling parameter () was 0.17. Transpiration rates were not driven directly by net radiation, but were closely linked to the size of the regional saturation deficit imposed at the level of the canopy by efficient overhead mixing, and were constrained by a large bulk stomatal resistance. A linear relationship between r ST and the saturation deficit is proposed as a realistic method for estimating transpiration for water yield studies of tussock catchments.  相似文献   

18.
A Forest SO2 Absorption Model (ForSAM) was developed to simulate (1) SO2 plume dispersion from an emission source, (2) subsequent SO2 absorption by coniferous forests growing downwind from the source. There are three modules: (1) a buoyancy module, (2) a dispersion module, and (3) a foliar absorption module. These modules were used to calculate hourly abovecanopy SO2 concentrations and in-canopy deposition velocities, as well as daily amounts of SO2 absorbed by the forest canopy for downwind distances to 42 km. Model performance testing was done with meteorological data (including ambient SO2 concentrations) collected at various locations downwind from a coal-burning power generator at Grand Lake in central New Brunswick, Canada. Annual SO2 emissions from this facility amounted to about 30,000 tonnes. Calculated SO2 concentrations were similar to those obtained in the field. Calculated SO2 deposition velocities generally agreed with published values.Notation c air parcel cooling parameter (non-dimensional) - E foliar absorption quotient (non-dimensional) - f areal fraction of foliage free from water (non-dimensional) - f w SO2 content of air parcel - h height of the surface layer (m) - H height of the convective mixing layer (m) - H stack stack height (m) - k time level - k drag coefficient of drag on the air parcel (non-dimensional) - K z eddy viscosity coefficient for SO2 (m2·s–1) - L Monin-Obukhov length scale (m) - L A single-sided leaf area index (LAI) - n degree-of-sky cloudiness (non-dimensional) - N number of parcels released with every puff (non-dimensional) - PAR photosynthetically active radiation (W m–2) - Q emission rate (kg s–2) - r b diffusive boundary-layer resistance (s m–1) - r c canopy resistance (s m–1) - r cuticle cuticular resistance (s m–1) - r m mesophyllic resistance (s m–1) - r s stomatal resistance (s m–1) - r exit smokestack exit radius (m) - R normally distributed random variable with mean of zero and variance of t (s) - u * frictional velocity scale, (m s–1) - v lateral wind vector (m s–1) - v d SO2 dry deposition velocity (m s–1) - VCD water vapour deficit (mb) - z can mean tree height (m) - Z zenith position of the sun (deg) - environmental lapse rate (°C m–1) - dry adiabatic lapse rate (0.00986°C m–1) - von Kármán's constant (0.04) - B vertical velocities initiated by buoyancy (m s–1) - canopy extinction coefficient (non-dimensional) - ()a denotes ambient conditions - ()can denotes conditions at the top of the forest canopy - ()h denotes conditions at the top of the surface layer - ()H denotes conditions at the top of the mixed layer - ()s denotes conditions at the canopy surface - ()p denotes conditions of the air parcels  相似文献   

19.
Meteorological techniques were used to monitor evapotranspiration (ET) at two sites in a boreal forest drainage basin located in southeastern Manitoba, Canada. An energy balance method was used in which net radiation (R N ) and ground heat flux (G) were measured directly. Sensible heat flux (H) was measured by the eddy correlation technique using a propeller anemometer and a fine-wire thermocouple. The energy components were calculated hourly on-line, and data were collected reliably over a five-month period.The R N and H instruments were mounted above the forest canopy and simultaneous measurements of H at heights of 12 and 6 m were in good agreement. Measurements at an open bare rock site indicated that G could be a substantial fraction of the daily RN at some locations, but over longer time periods, it was a small fraction and, therefore, was ignored.The two measurement locations represented upland (open bedrock/jack pine forest) and lowland (aspen/willow forest) sites in the drainage basin. The mean daily value of R N - H at the upland site was 0.57 times the value at the lowland location owing to differences in R N , H, and G. The mean ratio of daily H/R N was 0.6 for the upland site and 0.4 for the lowland site. A basin-wide ET was calculated by weighting the values for the two sites in proportion to their areas. The measured ET agreed well with precipitation minus runoff for the basin. Differences between these two quantities in summer and fall were attributed to water release and storage by the ground, respectively.Issued as AECL-9153.  相似文献   

20.
Evapotranspiration is a major component of both the energy and water balances of wetland tundra environments during the thaw season. Reliable estimates of evapotranspiration are required in the analysis of climatological and hydrological processes occurring within a wetland and in interfacing the surface climate with atmospheric processes. Where direct measurements are unavailable, models designed to accurately predict evapotranspiration for a particular wetland are used.This paper evaluates the performance, sensitivity and limitations of three physically-based, one-dimensional models in the simulation of evaporation from a wetland sedge tundra in the Hudson Bay Lowland near Churchill, Manitoba. The surface of the study site consists of near-saturated peat soil with a sparse sedge canopy and a constantly varying coverage of standing water. Measured evaporation used the Bowen ratio energy balance approach, to which the model results were compared. The comparisons were conducted with hourly and daily simulations.The three models are the Penman-Monteith model, the Shuttleworth-Wallace sparse canopy model and a modified Penman-Monteith model which is weighted for surface area of the evaporation sources.Results from the study suggest that the weighted Penman-Monteith model has the highest potential for use as a predictive tool. In all three cases, the importance of accurately measuring the surface area of each evaporation source is recognized. The difficulty in determining a representative surface resistance for each source and the associated problems in modelling without it are discussed.

List of Symbols

Models BREB Bowen ratio energy balance - P-M Penman-Monteith combination - S-W Shuttleworth-Wallace combination - W-P-M Weighted Penman-Monteith combination Other AE Available energy-all surfaces - AE c Available energy-canopy (S-W, W-P-M) - AE s Available energy-bare soil (S-W, W-P-M) - AE w Available energy-open water (W-P-M) - C p Specific heat of air - D Vapor pressure deficit - DAI Dead area index - FAI Foliage area index - LAI Leaf area index - Q * Net radiation - Q e Latent heat flux-total - Q ec Latent heat flux-canopy (S-W, W-P-M) - Q es Latent heat flux-bare soil (S-W, W-P-M) - Q ew Latent heat flux-open water (W-P-M) - Q g ground heat flux - Q h Sensible heat flux - S Proportion of area in bare soil - W Proportion of surface in open water - r a Aerodynamic resistance (P-M, W-P-M) - r c Canopy resistance - r s Generalized optimized surface resistance - r st Stomatal resistance - r c a Bulk boundary layer resistance (S-W) - r s a Aerodynamic resistance below mean canopy level (S-W) - r s s Soil surface resistance (S-W, W-P-M) Greek Bowen ratio - Psychrometer constant - Air density - Slope of saturation vapour pressure vs temperature curve  相似文献   

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