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531.
W. Kohsiek C. Liebethal T. Foken R. Vogt S. P. Oncley Ch. Bernhofer H. A. R. Debruin 《Boundary-Layer Meteorology》2007,123(1):55-75
An important part of the Energy Balance Experiment (EBEX-2000) was the measurement of the net radiation and its components.
Since the terrain, an irrigated cotton field, could not be considered homogeneous, radiation measurements were made at nine
sites using a variety of radiation instruments, including pyranometers, pyrgeometers and net radiometers. At several of these
sites multiple instruments were employed, which enabled us to compare instruments and assess accuracies. At all sites the
outgoing longwave and shortwave radiation and the net radiation were measured, while the incoming radiation was supposed to
be uniformly distributed over the field and was therefore measured at three sites only. Net radiation was calculated for all
sites from the sum of its four components, and compared with the direct measurement of net radiometers. The main conclusions
were: (a) the outgoing shortwave radiation showed differences of up to 30 W m−2 over the field; the differences were not clearly related to the irrigation events; (b) the outgoing longwave radiation showed
differences of up to 50 W m−2; the differences increased during the periods of irrigation; (c) the net radiation showed differences of several tens of
W m−2 across the field, rising to 50 W m−2 or more during the periods of irrigation; (d) the net radiation is preferably to be inferred from its four components, rather
than measured directly, and (e) attention should be paid to the characteristics of pyranometers that measure the outgoing
radiation, and thus are mounted upside down, while they are commonly calibrated in the upward position. The error in the net
radiation at EBEX-2000 is estimated at max (25 W m−2, 5%) per site during the day and 10 W m−2 at night.
The National Center for Atmospheric Research is supported by the National Science Foundation. 相似文献
532.
Possible changes in various characteristics of precipitation (its amount, intensity, probability of days with precipitation, and its extreme regimes) in the regions of northern Eurasia in the 21st century are assessed. The data for the analysis were obtained from simulations using global climatic models: atmosphere-ocean general circulation model ECHAM5/MPI-OM and an intermediate-complexity model developed in the Institute of Atmospheric Physics, RAS. The simulations were performed for the SRES-A2 and SRES-B1 scenarios of anthropogenic emission of greenhouse gases into the atmosphere. The results obtained from models of two generations, i.e., ECHAM5/MPI-OM and ECHAM4/OPYC3, models were compared. Detailed analysis was performed for the basins of largest Siberian rivers, the Volga River, and the Caucasian region. 相似文献
533.
A Simplified Method for Vulnerability Assessment of Dwelling Buildings and Estimation of Damage Scenarios in Catalonia, Spain 总被引:1,自引:1,他引:1
A. Roca X. Goula T. Susagna J. Chávez M. González E. Reinoso 《Bulletin of Earthquake Engineering》2006,4(2):141-158
A simplified method for vulnerability assessment of dwelling buildings with a statistical approach at a regional scale based on the EMS’98 is proposed. It is presented some applications of this methodology in Catalonia, Spain: (i) tools for generation of damage scenarios for preventive purposes; (ii) simulation of damages of historical earthquakes if they would occur today; and (iii) territory zonation to establish the criteria for activating the different levels of earthquake emergency actions. 相似文献
534.
Most of the finite element analyses of reinforced concrete structures are restricted to two‐dimensional elements. Three‐dimensional solid elements have rarely been used although nearly all reinforced concrete structures are under a triaxial stress state. In this work, a three‐dimensional solid element based on a smeared fixed crack model that has been used in the past mainly for monotonic static loading analysis is extended to cater for dynamic analysis. The only material parameter that needs to be input for this model is the uniaxial compressive strength of concrete. Steel bars are modelled as uniaxial elements and an embedded formulation allows them to have any orientation inside the concrete elements. The proposed strategy for loading or unloading renders a numerical procedure which is stable and efficient. The whole process is applied to two RC frames and compared against existing experiments in the literature. Results show that the proposed approach may adequately be used to predict the dynamic response of a structure. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
535.
J. Fuhrer M. Beniston A. Fischlin Ch. Frei S. Goyette K. Jasper Ch. Pfister 《Climatic change》2006,79(1-2):79-102
There is growing evidence that, as a result of global climate change, some of the most severe weather events could become more frequent in Europe over the next 50 to 100 years. The paper aims to (i) describe observed trends and scenarios for summer heat waves, windstorms and heavy precipitation, based on results from simulations with global circulation models, regional climate models, and other downscaling procedures, and (ii) discuss potential impacts on agricultural systems and forests in Switzerland. Trends and scenarios project more frequent heavy precipitation during winter corresponding, for example, to a three-fold increase in the exceedance of today's 15-year extreme values by the end of the 21st century. This increases the risk of large-scale flooding and loss of topsoil due to erosion. In contrast, constraints in agricultural practice due to waterlogged soils may become less in a warmer climate. In summer, the most remarkable trend is a decrease in the frequency of wet days, and shorter return times of heat waves and droughts. This increases the risk of losses of crop yield and forage quality. In forests, the more frequent occurrence of dry years may accelerate the replacement of sensitive tree species and reduce carbon stocks, and the projected slight increase in the frequency of extreme storms by the end of the century could increase the risk of windthrow. Some possible measures to maintain goods and services of agricultural and forest ecosystems are mentioned, but it is suggested that more frequent extremes may have more severe consequences than progressive changes in means. In order to effectively decrease the risk for social and economic impacts, long-term adaptive strategies in agriculture and silviculture, investments for prevention, and new insurance concepts seem necessary. 相似文献
536.
537.
538.
Additional analytical data for the thirteen oxides usually determined in a rock analysis by wet methods and estimates and, conclusions from the analysis of variance are presented for the eight new USGS rock standards STM-1, RGM-1, QLO-1, SCo-1, MAG-1, SDC-1, BHVO-1 and SGR-1. The "single-solution" method of sample dissolution, and the "rapid methods" described by Shapiro were used. Three bottles of each standard were analyzed in duplicate, providing six replicate analyses of each sample. Relative standard deviations ranged from 0. 00 to 202 %, with only 12 of the possible 104 sample-oxide combinations exceeding 10 %. Most deviations exceeding 10 % occur with oxides at very low concentrations or with the determi-nation, of H2 O+ and CO2 , all of which often yield poor precision. These data indicate that the rapid wet chemical methods, except possibly for H2 O+ and CO2 , or when very low concentrations are present, can be considered reliable. Of the 104 F-ratios calculated during the analysis of variance for sample-oxide combinations, only eight equal or exceed the tabled value of 9. 55 for F0.95 (d. f. 2, 3). These data strongly support the conclusion that the contents of the bottles may be considered homogeneous for most oxides determined. When our data for an oxide in the several samples are plotted versus similar data in the USGS Prof. Paper 840 by several methods, the plots generally show good agreement for most sample-oxide combinations, but approximately thirty of the 104 show substantial differences, with no obvious correlation between the various methods used or the nature or magnitude of the differences. 相似文献
539.
540.
We present here experimental determinations of mass accommodation coefficients using a low pressure tube reactor in which monodispersed droplets, generated by a vibrating orifice, are brought into contact with known amounts of trace gases. The uptake of the gases and the accommodation coefficient are determined by chemical analysis of the aqueous phase.We report in this article measurements of exp=(6.0±0.8)×10–2 at 298 K and with a total pressure of 38 Torr for SO2, (5.0±1.0)×10–2 at 297 K and total pressure of 52 Torr for HNO3, (1.5±0.6)×10–3 at 298 K and total pressure of 50 Torr for NO2, (2.4±1.0)×10–2 at 290 K and total pressure of 70 Torr for NH3.These values are corrected for mass transport limitations in the gas phase leading to =(1.3±0.1)×10–1 (298 K) for SO2, (1.1±0.1)×10–1 (298 K) for HNO3, (9.7±0.9)×10–2 (290 K) for NH3, (1.5±0.8)×10–3 (298 K) for NO2 but this last value should not be considered as the true value of for NO2 because of possible chemical interferences.Results are discussed in terms of experimental conditions which determine the presence of limitations on the mass transport rates of gaseous species into an aqueous phase, which permits the correction of the experimental values. 相似文献