Modelling of evaporation in a sparse millet crop using a two-source model including sensible heat advection within the canopy     

M. R. Lund  H. Soegaard 《Journal of Hydrology》2003,280(1-4):124-144

During two successive growing seasons meteorological measurements were made in a pearl millet field in the Sahel to investigate the evaporation process in relation to crop growth. The evaporation was measured by eddy correlation and simulated using the Shuttleworth Wallace (SW) model [Q. J. R. Meteorol. Soc. 111 (1985) 839–855]. To take sun height and multi-layer scattering into account a radiation balance model was formulated. The model indicates that partitioning of the net radiation between the vegetation and the soil may be estimated (r²=0.94) from the fraction of diffuse radiation, the leaf area index and an attenuation coefficient, but that the attenuation coefficient may not be similar in different locations. To solve the SW-model with respect to the soil resistance an iterative solution was employed with the total evaporation estimated from the Bowen-ratio calculated from eddy correlation measurements. The procedure made it possible to derive stable estimates of soil resistance at soil evaporation rates down to 25 W m⁻². The soil resistance was found to be in accordance with evaporation through a dry surface layer. The SW-model indicates, that advection of sensible heat from the dry soil to the plants, increases transpiration considerably. This will cause management techniques, such as mulching and dry farming, aimed at reducing soil evaporation to be less effective than might be anticipated. The effects of raising the leaf area index to improve the microclimate is discussed in relation to management of the available water and crop security.  相似文献   

全球地壳运动的背景场及其研究进展   总被引：1，自引：0，他引：1  

金双根  朱文耀 《地球科学进展》2002,17(5):782-786

全球地壳运动是在全球地壳运动背景场中发生的，其背景场的运动参数是表征地壳运动的最基本特征。由于现今板块运动模型ITRF序列均忽略板块边界部分，并且板块以NUVEL1A模型来划分，由此建立的全球板块运动模型不能作为一个严格的全球地壳运动背景场。利用区域速度场和ITRF2000速度场建立一个包括非刚体的板块边界区域和刚体板块的全球地壳运动模型，其板块总角动量ΙLΙ＝0．131°/Ma，即不为零，存在整体旋转，由此建立无整体旋转（NNR）模型，并评述其研究进展。  相似文献   

基于.NET的应用气象网站及电子公告牌(BBS)设计     

刘兴华  何险峰  秦明俊  唐良招 《高原山地气象研究》2002,22(3)

本文针对应用气象服务网站设计的需求,分析其在现有技术下应用开发的实际经验,提出相应的设计方案.  相似文献   

Model analysis of grazing effect on above-ground biomass and above-ground net primary production of a Mongolian grassland ecosystem     

Yuxiang Chen  Gilzae Lee  Takehisa Oikawa 《Journal of Hydrology》2007,333(1):155-164

  相似文献   

Long-term comparisons of net radiation calculation schemes   总被引：1，自引：0，他引：1  

J. H. Kjaersgaard  R. H. Cuenca  F. L. Plauborg  S. Hansen 《Boundary-Layer Meteorology》2007,123(3):417-431

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   

大亚湾网箱养殖区生物-化学特性与营养状况的周日变化     

黄洪辉  王寓平 《广东海洋大学学报》2001,21(2):35-43

根据1998年11月对大亚湾大鹏澳网箱养殖区进行的定点24h连续水质监测资料,分析并讨论了该养殖区海水生物-化学各要素的垂直分布和周日变化规律,并用单项指标评价法和改进的营养状态质量指数(NQI)法,参照营养指数(E)对该网箱养殖区海水的营养状况进行了评价和研究.结果表明,各项要素的平均值大都是表层＞中层＞底层;周日变化主要受潮汐运动和海水中生物的节律性生理活动的综合影响;表层海水的富营养化率明显高于中层海水,其各单项指标处于中度一富营养状态,而中层和底层海水则分别处于贫一中度和贫-富营养状态;PO4-P相对较贫乏,为养殖区富营养化的最关键限制因素.  相似文献   

Electron density distribution and bond critical point properties for forsterite, Mg2 SiO4, determined with synchrotron single crystal X-ray diffraction data     

A. Kirfel  T. Lippmann  P. Blaha  K. Schwarz  D. F. Cox  K. M. Rosso  G. V. Gibbs 《Physics and Chemistry of Minerals》2005,32(4):301-313

A generalized X-ray scattering factor model experimental electron density distribution has been generated for the orthosilicate forsterite, using an essentially extinction and absorption free set of single crystal diffraction data recorded with intense, high energy synchrotron X-ray radiation (E=100.6 keV). A refinement of the model converged with an R(F)=0.0061. An evaluation of the bond critical point, bcp, properties of the distribution at the (3, –1) stationary points for the SiO and MgO bonded interactions, yielded values that agree typically within ~5%, on average, with theoretical values generated with quantum chemical computational strategies, using relatively robust basis sets. On the basis of this result, the modeling of the experimental distribution is considered to be adequate. As the bcp properties increase in magnitude, the MgO and SiO bonds decrease in length as calculated for a number of rock forming silicates. As asserted by Coppens (X-ray charge densities and chemical bonding. Oxford University Press, Oxford, 1997), large negative ²(r_c) values, characteristic of shared interactions involving first row atoms, may not be characteristic of closed shell covalent bonded interactions involving second row Si, P and S atoms bonded to O. This study adds new evidence to the overall relatively good agreement between theoretical bcp properties generated with computational quantum strategies, on the one hand, and experimental properties generated with single crystal high energy synchrotron diffraction data on the other. The similarity of results not only provides a basis for using computational strategies for studying and modeling structures, defects and the reactivity of representative structures, but it also provides a basis for improving our understanding of the crystal chemistry of earth materials and the character of the SiO bonded interaction.  相似文献   

地震信息资源的开发利用     

梁凯利  赵小倩 《高原地震》2000,12(4):64-67

探索了网络环境下地震信息的开发利用,提出了加快发展的对策。  相似文献   

中国不同气候带各类型森林的生物量和净第一性生产力   总被引：27，自引：0，他引：27  

李高飞  任海 《热带地理》2004,24(4):306-310

根据<中国植被>的区划,将收集的全国984个样点的森林数据归并到5种气候带类型中,计算了各类型森林以及同一类型森林(分人工林和天然林)的生物量和净第一性生产力,还计算了不同气候带森林各器官的平均生物量和净第一性生产力.结果表明,从寒温带到热带各类型森林的生物量和净第一性生产力逐渐增加,天然林的生物量大于人工林生物量;除热带林外,人工林的净第一性生产力大于天然林净第一性生产力.  相似文献   

Production and respiration control the marine microbial metabolic balance in the eastern North Atlantic subtropical gyre     

María Aranguren-Gassis  Pablo SerretEmilio Fernández  Juan L. HerreraJose F. Domínguez  Valesca PérezJose Escanez 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(7):768-775

Two main contrasted hypotheses have arisen during the last decades about the factors controlling the planktonic net metabolic balance in oligotrophic waters: gross primary production controls net community production vs. variability of net community production is also influenced by changes in microbial respiration. This work discusses both hypotheses analyzing the variability of metabolic rates along a gradient from the margin to the centre of the North Atlantic oligotrophic gyre, i.e. from relatively productive to more oligotrophic conditions. Net community production (NCP) was close to zero (between −3.34 and −11.77 mmol O₂ m⁻² d⁻¹) at the margin of the gyre and tended towards net heterotrophy (−44.03 mmol O₂ m⁻² d⁻¹) to the centre of the gyre as both gross primary production (GPP) and community respiration (CR) decreased. The strong relationships found between nutrient availability and both NCP and GPP suggest that factors controlling GPP are prevalent in determining NCP variability in this biogeographic region. However implementation of existing models to predict NCP from the measured GPP indicates that the precise estimation of NCP in different oligotrophic systems requires consideration of the magnitude and variability of microbial respiration rates.  相似文献