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1.
Abstract

Analysis of radiation data from Suffield, Alberta and Swift Current, Saskatchewan reveals discrepancies that are strongly linked to changes in the actual and assigned calibration factors of the pyranometers used at those locations.  相似文献   

2.
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   

3.
Abstract

This paper describes the observational framework for the research reported within this Special Issue. The validation of the ERS‐1 synthetic aperture radar (SAR) for ocean wave measurement was the primary goal and focus; secondary goals were the validation of wave models and marine radars and the investigation of the wind stress/sea‐state relation in the open ocean.

The planned focus of the observations on the ERS‐1 crossover node location and pass times over the Grand Banks of Newfoundland, and on the grid points of the Atmospheric Environment Service's operational wave prediction model, has produced the opportunity for an accurate calibration and a relevant validation of the ERS‐1 SAR, the wave model and the marine radars.

The observations, made on the Grand Banks in winter, strongly emphasize the complexity of the atmospheric and wave fields encountered in the open sea at these latitudes. Their interpretation will provide a challenge, and will require consideration of a wide variety of data sources, both remotely sensed and in situ, all assimilated in the framework of physical ocean models.  相似文献   

4.
Abstract

The performances of eight methods for estimating daily energy‐limited evapotranspiration (Ee) were compared with reliable values for the Peace River region of British Columbia. They included the methods of Priestley and Taylor (PT), Jensen and Haise (JH), Hargreaves (H) and Makkink (M), the first and second equations of Baier and Robertson (BR1 and BR2), and the modified methods of Blaney and Criddle (BC) and Thornthwaite (T). The reference data were obtained from previous workers, who in 1977 and 1979 made micrometeorological measurements of Ee using the Bowen ratio method.

The relationships between estimated and measured Ee values excluding the T method in 1977 had correlation coefficients (R) ranging from 0.65 to 0.84. These were not significantly different at the 5% level. The Standard Errors of the Estimate (SEE) ranged from 0.43 to 1.69 mm d?1. The PT, JH, BR1 and T methods had low SEE values, whereas the BR2, H, BC and M methods had high SEE values. Six of the eight methods (PT, JH, H, M, BR2 and BC) were calibrated for local conditions using 1979 data. After calibration, the methods were tested with the 1977 data. The results indicated significant improvement in the fit of four of the methods (H, M, BR2 and BC). Overall, it was concluded that after calibration, six of the eight methods had predictive power and fit that were not significantly different at the 5% level.  相似文献   

5.
Summary Soil heat flux transducer calibration, according to theory, is influenced by the thermal conductivity difference between the transducer and the calibration medium and the geometry of the transducer. This study was conducted to compare the influence of these parameters on the calibration factors of two types of commercial soil heat flux transducers with different material thermal conductivities and different geometries. A theoretical calibration equation was developed and evaluated. Calibrations of 14 transducers representing two commercial types were conducted in the laboratory using steady-state conductive methods over a range of heat fluxes from 40 W/m2 to 200 W/m2. The calibration medium was dry and saturated sand with a thermal conductivity varying from 0.3 to 3 W m–1°C–1. The mean calibration factor for one type of transducer was 12% lower than the mean manufacturer's calibration factor instead of the 26 to 36% lower value predicted by theory. The other type of transducer had a mean calibration factor 7% greater than the mean manufacturer's calibration factor in contrast to the 1 to 11% larger value predicted from theory. The computed geometric factors were 1.07 and 0.89 for the circular and square transducers, respectively. These factors were less than the theoretical value of 1.70 for each shape of transducer but similar to experimental values of 1.02 to 1.31 from previous studies reported in the literature. The thermal conductivity of the calibration medium and the geometry of the transducer affects the calibration factors of soil heat flux transducers, basically according to theory.Contribution from USDA-Agricultural Research Service, Southern Plains Area.With 4 Figures  相似文献   

6.
The pyranometer for observing the solar radiation reaching the surface of the earth is manufactured by various companies around the world. The sensitivity of the pyranometer at the observatory is required to be properly controlled based on the reference value of the World Radiometric Center (WRC) and the observatory environment; otherwise, the observational data may be subject to a large error. Since the sensitivity of the pyranometer can be calibrated in an indoor or outdoor calibration, this study used a CSTM-USS-4000C Integrating Sphere by Labsphere Inc. (USA) to calibrate the sensitivity of CMP22 pyranometer by Kipp&Zonen Inc. (Netherlands). Consequently, the factory sensitivity of CMP22 was corrected from 8.68 μV·(Wm?2)?1 to 8.98 μV·(Wm?2)?1, and the result from the outdoor calibration according to the observatory environment was 8.90 μV·(Wm?2)?1. After the indoor calibration of the pyranometer sensitivity, the root mean square error (RMSE) of the observational data at the observatory on a clear day without clouds (July 13, 2017) was 7.11 Wm?2 in comparison to the reference pyranometer. After the outdoor calibration of the pyranometer sensitivity based on these results, the RMSE of the observational data was 1.74 Wm?2 on the same day. Periodic inspections are required because the decrease of sensitivity over time is inevitable in the pyranometer data produced at the observatory. The initial sensitivity after indoor calibration (8.98 μV·(Wm?2)?1) is important, and the sensitivity after outdoor calibration (8.90 μV·(Wm?2)?1) can be compared to the data at the Baseline Surface Radiation Network (BSRN) or can be used for various studies and daily applications.  相似文献   

7.
This paper is a comparative study between the two most common hailpad calibration systems: one annual calibration of a whole consignment of material, and the individual calibration of each plate after a hailfall. Individual calibration attempts to minimize errors due to differences in sensitivity to the impact of hailstones between plates from the same consignment, or due to differences in the inking process before the actual measurement.The comparison was carried out using calibration data from the past few years in the hailpad network in south-western France, and data from an individual calibration process on material provided by the hailpad network in Lleida (Spain). The same type of material was used in the two cases.The results confirm that the error in measuring hailstone sizes is smaller in the case of an individual calibration of hailpads than when one single calibration process was carried out for a whole consignment. The former is approximately 80% of the latter. However, this error could have been higher if it had not been the same person carrying out the single calibration process and the measuring of the dents: it has been found that differences in the inking process may account for up to 20% of the error in the case of small hailstones. Calibration errors affecting other variables, e.g. energy or parameter λ of the exponential size distribution are generally higher (5% and 18%, respectively) than errors due to the spatial variability of the hailstones. However, the calibration method does not influence the maximum size, since the relative error attributed to the spatial variability is about 8 times the calibration error.In conclusion, if errors in determining energy or parameter λ are to be reduced to a minimum, it is highly advisable to be consistent in applying the measuring procedure (if possible with the same person carrying out the measurements all the time), and even to use individual calibration on each plate, always bearing in mind that technicians have to be trained appropriately in order to achieve the highest possible degree of uniformity.  相似文献   

8.
Abstract

The Purple Crow Lidar (PCL) is a large power-aperture product monostatic laser radar which until 2010 was located at the Delaware Observatory (42°52′N, 81°23′W, 225 m elevation above sea level) near the campus of the University of Western Ontario. It is capable of measuring temperature from 10 to 110 km altitude, as well as water vapour in the troposphere and stratosphere. We use upper tropospheric and stratospheric vibrational Raman N2 backscatter-derived temperatures to form a climatology for the years 1999 to 2007 from 10 to 40 km attitude. The lidar temperatures are validated using nearby radiosonde measurements from Detroit and Buffalo. The measured temperatures show good agreement with the radiosonde soundings. An agreement of ±1 K is found during the summer months and ±2.5 K during the winter months, validating the calibration of the lidar to within the geophysical variability of the measurements. Comparison between the PCL measurements and the Committee on Space Research International Reference Atmosphere, 1986 (CIRA-86) and the Mass Spectrometer Incoherent Scatter-90 (MSIS-90) models show the models are as much as 5 K warmer below 25 km and 2 to 4 K colder above 25 km during the summer months, in large part because the measured tropopause height is consistently lower than in the models.  相似文献   

9.
1 (1 Numerical Studies of the Energy and Water Cycle of the BALTIC Region) stands for two international projects funded by the European Community in the years 1996–2000. The campaign was embedded into the continental-scale experiment BALTEX2(2 Baltic Sea Experiment), a subproject of GEWEX3(3 Global Energy and Water Cycle Experiment) (Raschke, 1994; Bengtsson, 1995). The present special issue emerged from two NEWBALTIC progress meetings held in Sweden: One in June 1999 in Abisko and one in January 2000 at Chalmers University of Technology in Gothenburg. The NEWBALTIC community welcomed the suggestion of Professor Bengtsson, Chairman of the BALTEX Science Steering Group, to present selected contributions of the considerable body of NEWBALTIC results in a special MAP4(4 Meterology and Atmospheric Physics) issue. This collection, it was agreed, might serve as an example for the current state of modelling hydro-meteorological key processes on the continental scale of the Baltic Sea and its environment (see also Raschke et al., 1998, 2001). All papers submitted went through the review process regularly applied by MAP. The present special issue is opened by a review paper of Lennart Bengtsson on the objectives of BALTEX and on the central goal of the NEWBALTIC project: The energy and water cycle of the Baltic Sea. BALTEX in general was planned as a decade-long endeavour with a preparatory phase 1992–1993, a build-up phase 1994–1996 and a major research phase 1997–2001. Most of the work within the two NEWBALTIC projects have been carried out during the major research phase. In the words of the project folder distributed early in the 90ies: BALTEX, as a research programme integrating three disciplines into one single project, will be mutually stimulating and is expected to overcome traditional embarrassing barriers between meteorological, hydrological and oceanographic research. NEWBALTIC, as an important component of BALTEX, has done a visible step into this direction. Concerning the specific time periods chosen, most of the NEWBALTIC studies of this issue concentrate upon a three months period August-September-October 1995 referred to as PIDCAP5.(5 Pilot Study of Intense Data Collection and Analysis of Precipitation) The total of 13 papers eventually selected for publication in the present special issue are devoted to the two central aspects of the NEWBALTIC campaign: To understand the processes as represented in modern high-resolution coupled models, and to evaluate and digest observed data. So the papers of the present issue have been grouped into these two categories.  相似文献   

10.
A high resolution global model of the terrestrial biosphere is developed to estimate changes in nitrous oxide (N2O) emissions from 1860–1990. The model is driven by four anthropogenic perturbations, including land use change and nitrogen inputs from fertilizer, livestock manure, and atmospheric deposition of fossil fuel NO x . Global soil nitrogen mineralization, volatilization, and leaching fluxes are estimated by the model and converted to N2O emissions based on broad assumptions about their associated N2O yields. From 1860–1990, global N2O emissions associated with soil nitrogen mineralization are estimated to have decreased slightly from 5.9 to 5.7 Tg N/yr, due mainly to land clearing, while N2O emissions associated with volatilization and leaching of excess mineral nitrogen are estimated to have increased sharply from 0.45 to 3.3 Tg N/yr, due to all four anthropogenic perturbations. Taking into account the impact of each perturbation on soil nitrogen mineralization and on volatilization and leaching of excess mineral nitrogen, global 1990 N2O emissions of 1.4, 0.7, 0.4 and 0.08 Tg N/yr are attributed to fertilizer, livestock manure, land clearing and atmospheric deposition of fossil fuel NO x , respectively. Consideration of both the short and long-term fates of fertilizer nitrogen indicates that the N2O/fertilizer-N yield may be 2% or more.C. NBM Definitions AET mon (cm H2O) = monthly actual evapotranspiration - AET ann (cm H2O) = annual actual evapotranspiration - age h (years) = stand age of herbaceous biomass - age w (years) = stand age of woody biomass - atmblc (gC/m2/month) = net flux of CO2 from grid - biotoc (gC/g biomass) = 0.50 = convert g biomass to g C - beff h = 0.8 = fraction of cleared herbaceous litter that is burned - beff w = 0.4 = fraction of cleared woody litter that is burned - bfmin = 0.5 = fraction of burned N litter that is mineralized or converted to reactive gases which rapidly redeposit. Remainder assumed pyrodenitrified to N2. + N2O - bprob = probability that burned litter will be burned - burn h (gC/m2/month) = herbaceous litter burned after land clearing - burn w (gC/m2/month) = woody litter burned after land clearing - cbiomsh (gC/m2) = C herbaceous biomass pool - cbiomsw (gC/m2) = C woody biomass pool - clear (gC/m2/month) = woody litter C removed by land clearing - clearn (gN/m2/month) = woody litter N removed by land clearing - cldh (month–1) = herbaceous litter decomposition coefficient - cldw (month–1) = woody litter decomposition coefficient - clittrh (gC/m2) = C herbaceous litter pool - clittrw (gC/m2) = C woody litter pool - clph (month–1) = herbaceous litter production coefficient - clpw (month–1) = woody litter production coefficient - cnrath (gC/gN) = C/N ratio in herbaceous phytomass - cnrats (gC/gN) = C/N ratio in soil organic matter - cnratt (gC/gN) = average C/N ratio in total phytomass - cnratw (gC/gN) = C/N ratio in woody phytomass - crod (month–1) = forest clearing coefficient - csocd (month–1) = actual soil organic matter decompostion coefficient - decmult decomposition coefficient multiplier; natural =1.0; agricultural =1.0 (1.2 in sensitivity test) - fertmin (gN/m2/month) = inorganic fertilizer input - fleach fraction of excess inorganic N that is leached - fligh (g Lignin/ g C) = lignin fraction of herbaceous litter C - fligw (g Lignin/ g C) = 0.3 = lignin fraction of woody litter C - fln2o = .01–.02 = fraction of leached N emitted as N2O - fnav = 0.95 = fraction of mineral N available to plants - fosdep (gN/m2/month) = wet and dry atmospheric deposition of fossil fuel NO x - fresph = 0.5 = fraction of herbaceous litter decomposition that goes to CO2 respiration - fresps = 0.51 + .068 * sand = fraction of soil organic matter decomposition that goes to CO2 respiration - frespw = 0.3 * (* see comments in Section 2.3 under decomposition) = fraction of woody litter decomposition that goes to CO2 respiration - fsoil = ratio of NPP measured on given FAO soil type to NPFmiami - fstruct = 0.15 + 0.018 * ligton = fraction of herbaceous litter going to structural/woody pool - fvn2o = .05–.10 = fraction of excess volatilized mineral N emitted as N2O - fvol = .02 = fraction of gross mineralization flux and excess mineral N volatilized - fyield ratio of total agricultural NPP in a given country in 1980 to total NPPmiami of all displaced natural grids in that country - gimmob h (gN/m2/month) = gross immobilization of inorganic N into microbial biomass due to decomposition of herbaceous litter - gimmob s (gN/m2/month) = gross immobilization of inorganic N into microbial biomass due to decomposition of soil organic matter - gimmob w (gN/m2/month) = gross immobilization of inorganic N into microbial biomass due to decomposition of woody litter - graze (gC/m2/month) = C herbaceous biomass grazed by livestock - grazen (gN/m2/month) = N herbaceous biomass grazed by livestock - growth h (gC/m2/month) = herbaceous litter incorporated into microbial biomass - growth w (gC/m2/month) = woody litter incorporated into microbial biomass - gromin h (gN/m2/month) = gross N mineralization due to decomposition and burning of herbaceous litter - gromin s (gN/m2/month) = gross N mineralization due to decomposition of soil organic matter - gromin w (gN/m2/month) = gross N mineralization due to decomposition and burning of woody litter - herb herbaceous fraction by weight of total biomass - leach (gN/m2/month) = leaching (& volatilization) losses of excess inorganic N - ligton (g lignin-C/gN) = lignin/N ratio in fresh herbaceous litter - LP h (gC/m2/month)= C herbaceous litter production - LP (gC/m2/month) = C woody litter production - LPN h (gN/m2/month) = N herbaceous litter production - LPN W (gN/m2/month) = N woody litter production - manco2 (gC/m2/month) = grazed C respired by livestock - manlit (gC/m2/month) = C manure input (feces + urine) - n2oint (gN/m2/month) = intercept of N2O flux vs gromin regression - n2oleach (gN/m2/month) = N2O flux associated with leaching and volatilization of excess inorganic N - n2onat (gN/m2/month) = natural N2O flux from soils - n2oslope slope of N2O flux vs gromin regression - nbiomsh (gN/m2) = N herbaceous biomass pool - nbiomsw (gN/m2) = N woody biomass pool - nfix (gN/m2/month) = N2 fixation + natural atmospheric deposition - nlittrh (gN/m2) = N herbaceous litter pool - nlittrw (gN/m2) = N woody litter pool - nmanlit (gN/m2/month) = organic N manure input (feces) - nmanmin (gN/m2/month) = inorganic N manure input (urine) - nmin (gN/m2) = inorganic N pool - NPP acth (gC/m2/month)= actual herbaceous net primary productivity - NPP actw (gC/m2/month) = actual woody net primary productivity - nvol (gN/m2/month) = volatilization losses from inorganic N pool - plntnav (gN/m2/month)= mineral N available to plants - plntup h (gN/m2/month) = inorganic N incorporated into herbaceous biomass - plntup w (gN/m2/month) = inorganic N incorporated into woody biomass - precip ann (mm) = mean annual precipitation - precip mon (mm) = mean monthly precipitation - pyroden h (gN/m2/month) = burned herbaceous litter N that is pyrodenitrified to N2 - pyroden w (gN/m2/month) = burned woody litter N that is pyrodenitrified to N2 - recyc fraction of N that is retranslocated before senescence - resp h (gC/m2/month) = herbaceous litter CO2 respiration - resp s (gC/m2/month) = soil organic carbon CO2 respiration - resp w (gC/m2/month) = woody litter CO2 respiration - sand sand fraction of soil - satrat ratio of maximum NPP to N-limited NPP - soiloc (gC/m2) = soil organic C pool - soilon (gN/m2) = soil organic N pool - temp ann (°C) = mean annual temperature - temp mon (°C) = mean monthly temperature Now at the NOAA Aeronomy Laboratory, Boulder, Colorado.  相似文献   

11.
Abstract

Satellite observations revealed that there is a close relationship between perturbations of sea surface temperature (SST) and wind stress (τ) induced by tropical instability waves (TIWs; SSTTIW and τ TIW). Using the empirical relationship observed between TIW-induced wind stress divergence (curl) and downwind (crosswind) SST gradients, this study establishes a TIW-induced wind stress field perturbation model τ TIW?=?F(SST). This empirical model solves τ TIW from the TIW-induced wind stress divergence and curl, which are estimated from the downwind and crosswind SST gradients. This empirical τ TIW?=?F(SST) model can be incorporated into the ocean model to take into account the effect of τ TIW. By comparing two experiments with and without the τ TIW effect, this study demonstrates that τ TIW has a substantial effect on the equatorial Pacific heat budget and induces the long-term mean SST to exhibit a 0.2°C difference, which is consistent with previous studies.  相似文献   

12.
Abstract

Spectrometers are designed to isolate particular wavebands and suppress light from wavelengths outside the band of interest. However, a small amount of undesired light will always enter the detector, not through the designed optical path, but through random scattering from the instrument optical components, housing, and dust particles. Every spectrophotometer has stray light coming from outside the nominal measurement waveband. For Dobson spectrophotometers and single monochromator Brewer spectrophotometers, which are basic instruments in the World Meteorological Organization (WMO) ozone and ultraviolet (UV) monitoring network, the error introduced by stray light is substantial when the ozone slant path becomes very large because of high solar zenith angles and a thick ozone layer. These are common conditions during Arctic spring. To study the issue, a long ozone slant path Intercomparison/Calibration campaign for Nordic Brewers and Dobsons was held at Sodankylä 8–24 March 2011 and a follow-up campaign to extend calibrations to shorter ozone slant paths took place at Izaña observatory, Tenerife, between 28 October and 18 November 2011. These campaigns were part of the Committee on Earth Observation Satellites (CEOS) Intercalibration of Ground-based Spectrometers and Lidars project funded by the European Space Agency (ESA), intended to permit the homogenization of ozone data from the European ozone ground-truthing network. During the active intercomparison periods, measurements were taken only when good conditions for sun or moon observations existed. Laboratory measurements using calibration lamps and helium-cadmium (HeCd) lasers were an essential part of both campaigns. The campaigns produced a high-quality database of total ozone and UV measurements and an accurate, up-to-date calibration and characterization of participating Brewers and Dobsons against the European standard instruments from the Regional Dobson Calibration Centre-Europe (RDCC-E) and the Regional Brewer Calibration Centre-Europe (RBCC-E). In the present work we focus on single monochromator Brewers and present a physics-based method to compensate for the stray-light effects in ozone retrieval using laboratory characterizations and radiative transfer modelling. The method was tested with independent data from the campaign.  相似文献   

13.
S. Tabata 《大气与海洋》2013,51(3):237-247
Abstract

Observations of sea‐surface temperatures and salinities, made by a variety of methods during August and September 1975 in the northeast Pacifie Ocean, are examined to evaluate the quality of surface data. The bucket method is capable of providing sea‐surface temperatures to an accuracy (standard deviation) of ±0.15°C. The thermograph/salinograph when corrected by applying a “field‐calibration” value, gives temperatures with a standard deviation one half that obtained by the bucket method. Expendable bathythermograph temperatures were, on the average, 0.3°C urate as the true values. Were it not for this offset they would have been as accurate as those obtained with bucket thermometers. Engine‐intake temperatures observed by the engine‐room crew were, on the average, 0.3°C larger than the true values, but were characterized by large inaccuracies, with a standard deviation about an order of magnitude greater than those found for other methods. These variations are believed to be due to reading errors. Sea‐surface salinities observed with the bucket could be, with reasonable care, accurate within the limitation of the salinometer method used aboard ships. The quality of data has been found to vary significantly between observers. Results obtained from this cruise and from weathership data (1956–1976) suggest that the surface temperatures and salinities observed during the past, 1956–1962, in the northeast Pacific Ocean have generally been overestimated.  相似文献   

14.
We describe a new calibration procedure included in the production process of Scintec’s displaced-beam laser scintillometers (SLS-20/40) and its effect on their measurement accuracy. The calibration procedure determines the factual displacement distances of the laser beams at the receiver and transmitter units, instead of assuming a prescribed displacement distance of 2.70 mm. For this study, four scintillometers operated by Wageningen University and the German Meteorological Service were calibrated by Scintec and their data re-analyzed. The results show that significant discrepancies may exist between the factual and the prescribed displacement distances. Generally, the factual displacement is about 0.1 mm smaller than 2.70 mm, but extremes varied between 0.04 and 0.24 mm. Correspondingly, using non-calibrated scintillometers may result in biases as large as 20 % in the estimates of the inner-scale length, $l_{0}$ , the structure parameter of the refractive index, $C_{n_{_2}}$ , and the friction velocity, $u_{*}$ . The bias in the sensible heat flux was negligible, because biases in $C_{n_{_2}}$ and $u_{*}$ cancel. Hence, the discrepancies explain much of the long observed underestimations of $u_{*}$ determined by these scintillometers. Furthermore, the calibration improves the mutual agreement between the scintillometers for $l_{0}$ , but especially for $C_{n_{_2}}$ . Finally, it is noted that the measurement specifications of the scintillometer do not expire and hence the results of the calibration can be applied retroactively.  相似文献   

15.
Long-term comparisons of net radiation calculation schemes   总被引：1，自引：0，他引：1  
Six commonly used models for calculating daily net radiation were tested against measured net radiation. Meteorological data from 32 and 7 consecutive years obtained at two temperate sites were used. The extensive duration of the datasets ensured that all weather conditions and extreme events were captured. A set of statistical procedures was used to evaluate the performance of the models. The mean bias errors ranged from 0.0 W m−2 to 24.8 W m−2 and 0.1–24.7 W m−2 and root mean square error from 11.0 W m−2 to 28.1 W m−2 and 10.0–27.9 W m−2 at the two sites respectively, for days without snow cover on the ground. The best agreement was found when locally calibrated model coefficients were used. Only negligible differences in model performances were found between the two sites and the differences were lower than the inaccuracies of the net radiation instruments used. Including days with snow cover in the analysis lead to a slight increase in the bias and scatter of the predictions. Model performances were in general better during summertime than wintertime. Altered albedo values during winter caused by generally low sun angles were likely the cause of this. Analysis showed that at least 5 years of data were needed to obtain stable calibration coefficients for local calibration of the models. Based on the results from this study, and due to their physical background, two physical based models were recommended for calculating daily values of net radiation under temperate climate regimes. A simple adjustment of the calibration coefficients based on climate regime was suggested for these models.  相似文献   

16.
星载双频云雷达的云微物理参数反演算法研究   总被引：2，自引：1，他引：1  
使用星载雷达模拟器输出的模拟数据,为星载双频云雷达选择了最佳的频点组合,并开展了双频联合反演云微物理参数的算法研究。结果表明:（1）在位于大气窗口的6组频点组合中,94/220 GHz的组合对滴谱参数的微小变化较为敏感,有利于进行双频的联合反演。综合考虑不同频点的探测能力、衰减以及工业部门的制造水平后,认为94/220 GHz可以作为未来星载双频测云雷达的探测频点。（2）双频反演中最核心的双波长比（DWR）和体积中值直径（D0）的关系与冰晶粒子密度相关。当密度随着粒子直径变化时,DWR随着D0单调递增,当粒子密度固定不变时,DWR-D0曲线可能会出现非单调变化,从而使得固定密度时的反演比变密度时更加复杂。（3）后向迭代的双频反演算法同样适用于94/220 GHz进行云微物理参数的反演,并且对模拟数据的反演精度较高。此外,反演精度受到系统噪声以及定标精度的影响,为了满足反演精度的要求,系统噪声和定标误差应该控制在1 dBz以内。   相似文献   

17.
Abstract

The National Drought Model (NDM) is an amalgamation of the atmospheric component of the original Palmer Drought and Versatile Soil Moisture Budget (VSMB) models. The NDM uses locally derived coefficients from the station or gridded climate data to calculate a calibration factor for comparing locations in time and space. A modular approach is used to model major processes such as evapotranspiration, biometeorological time, snowmelt, and the cascading of soil moisture down to the root zone. The modular approach allows modifications to be made to specific sections without making structural changes to the entire model or the data inputs. The NDM is an operational tool, integrating data from the climate, soil, and plant sciences to monitor agroclimatic risks such as drought and excess moisture. In this paper, the capacity of the NDM to monitor extreme agroclimatic risks, such as drought and flooding of agricultural soils, was assessed. Using the Palmer Drought Severity Index component of the NDM, the mapping of the spatial extent and severity of the 2001 and 2002 droughts across Canada and the excess moisture conditions on the Canadian Prairies in 2010 agreed with other assessments. The validation study of soil moisture at two Alberta locations (Lethbridge and Beaverlodge) showed that the VSMB tracked the soil moisture flux in the root zone successfully in response to changing environmental conditions. The VSMB explained about 70 and 60% of the variance in observed soil moisture at the two respective locations.  相似文献   

18.
Calibration of tipping bucket rain gauges in the Graz urban research area   总被引：2，自引：0，他引：2  
The Institute of Urban Water Management and Landscape Water Engineering of the Graz University of Technology (Austria) operates a hydrological research area in the City of Graz. In this urban research area precipitation and runoff data are collected by order of the municipality of Graz. At present precipitation data are measured by seven tipping bucket rain gauges. Comparative measurements have shown a deviation between the recorded and the actual precipitation intensity. This made the institute calibrate the rain gauges periodically. In the middle of the 1990s, the development of a field calibration kit was started. Based on the experiences with the first field calibration kit, a microprocessor controlled device was developed. With this calibration device, the tipping bucket rain gauges are calibrated at regular intervals. In this paper the calibration process and the current results for seven rain gauges are discussed. The calibration process is dynamic calibration and uses a peristaltic pump. Not all of the tipping buckets investigated underestimate the rain intensity in the whole measuring range. Several rain gauges have a positive relative deviation, not exceeding 22%, in the low intensity range up to 0.5 mm/min. Positive deviation can be explained by retention of water in the buckets between tips. The reason for the negative deviation is the loss of water during the tips. It leads to the underestimate of the actual intensity. The largest relative deviation in the range of underestimate exceeds 30%. In the range of extreme intensities, the larger buckets (5 cm3) show a lower relative deviation than the smaller (2 cm3) buckets. The gauge characteristic can change in favourable or unfavourable directions after several years. Therefore, the calibration of tipping buckets is recommended at least every 2 to 3 years.  相似文献   

19.
The MAGICC (Model for the Assessment of Greenhouse gas Induced Climate Change) model simulation has been carried out for the 2000–2100 period to investigate the impacts of future Indian greenhouse gas emission scenarios on the atmospheric concentrations of carbon dioxide, methane and nitrous oxide besides other parameters like radiative forcing and temperature. For this purpose, the default global GHG (Greenhouse Gases) inventory was modified by incorporation of Indian GHG emission inventories which have been developed using three different approaches namely (a) Business-As-Usual (BAU) approach, (b) Best Case Scenario (BCS) approach and (c) Economy approach (involving the country’s GDP). The model outputs obtained using these modified GHG inventories are compared with various default model scenarios such as A1B, A2, B1, B2 scenarios of AIM (Asia-Pacific Integrated Model) and P50 scenario (median of 35 scenarios given in MAGICC). The differences in the range of output values for the default case scenarios (i.e., using the GHG inventories built into the model) vis-à-vis modified approach which incorporated India-specific emission inventories for AIM and P50 are quite appreciable for most of the modeled parameters. A reduction of 7% and 9% in global carbon dioxide (CO2) emissions has been observed respectively for the years 2050 and 2100. Global methane (CH4) and global nitrous oxide (N2O) emissions indicate a reduction of 13% and 15% respectively for 2100. Correspondingly, global concentrations of CO2, CH4 and N2O are estimated to reduce by about 4%, 4% and 1% respectively. Radiative forcing of CO2, CH4 and N2O indicate reductions of 6%, 14% and 4% respectively for the year 2100. Global annual mean temperature change (incorporating aerosol effects) gets reduced by 4% in 2100. Global annual mean temperature change reduces by 5% in 2100 when aerosol effects have been excluded. In addition to the above, the Indian contributions in global CO2, CH4 and N2O emissions have also been assessed by India Excluded (IE) scenario. Indian contribution in global CO2 emissions was observed in the range of 10%–26%, 6%–36% and 10%–38% respectively for BCS, Economy and BAU approaches, for the years 2020, 2050 and 2100 for P50, A1B-AIM, A2-AIM, B1-AIM & B2-AIM scenarios. CH4 and N2O emissions indicate about 4%–10% and 2%–3% contributions respectively in the global CH4 and N2O emissions for the years 2020, 2050 and 2100. These Indian GHG emissions have significant influence on global GHG concentrations and consequently on climate parameters like RF and ∆T. The study reflects not only the importance of Indian emissions in the global context but also underlines the need of incorporation of country specific GHG emissions in modeling to reduce uncertainties in simulation of climate change parameters.  相似文献   

20.
Summary ?The LITFASS project (‘Lindenberg Inhomogeneous Terrain – Fluxes between Atmosphere and Surface: a Long-term Study’) of the Deutscher Wetterdienst (DWD, German Meteorological Service) aims to develop and to test a strategy for the determination and parameterisation of the area-averaged turbulent fluxes of heat, momentum, and water vapour over a heterogeneous land surface. These fluxes will be representative for an area of about 10 * 10 km2 (while the typical patch size is between 10−1 to 100 km2) corresponding to the size of a grid cell in the present operational numerical weather prediction model of the DWD. LITFASS consists of three components: – the development of a non-hydrostatic micro-α-scale model (the LITFASS local model – LLM) with a grid-size of about 100 * 100 m2, – experimental investigations of land surface – atmosphere exchange processes and boundary layer structure within a 20 * 20 km2 area around the Meteorological Observatory Lindenberg, – the assimilation of a data base as an interface between measurements and modelling activities. The overall project strategy was tested over a three-week period in June 1998 during the LITFASS-98 field experiment. This paper gives an overview on the LITFASS project, on the design and measurement program of the LITFASS-98 experiment, and on the weather conditions during the period of the experiment. Conclusions are formulated for the operational realisation of the LITFASS measurement concept and for future field experiments aimed at studying the land surface – atmosphere interaction in the Lindenberg area. Selected results from both experimental and modelling activities are presented in a series of companion papers completing this special issue of the journal. Received June 18, 2001; revised March 18, 2002; accepted April 2, 2002  相似文献   

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