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31.
Daqing Yang Barry E. Goodison John R. Metcalfe Valentin S. Golubev Esko Elomaa Thilo Gunther Roy Bates Timothy Pangburn Clayton L. Hanson Douglas Emerson Voilete Copaciu Janja Milkovic 《水文研究》1995,9(8):877-895
The Tretyakov non-recording precipitation gauge has been used historically as the official precipitation measurement instrument in the Russian (formerly the USSR) climatic and hydrological station network and in a number of other European countries. From 1986 to 1993, the accuracy and performance of this gauge were evaluated during the WMO Solid Precipitation Measurement Intercomparison at 11 stations in Canada, the USA, Russia, Germany, Finland, Romania and Croatia. The double fence intercomparison reference (DFIR) was the reference standard used at all the Intercomparison stations in the Intercomparison. The Intercomparison data collected at the different sites are compatible with respect to the catch ratio (measured/DFIR) for the same gauge, when compared using mean wind speed at the height of the gauge orifice during the observation period. The Intercomparison data for the Tretyakov gauge were compiled from measurements made at these WMO intercomparison sites. These data represent a variety of climates, terrains and exposures. The effects of environmental factors, such as wind speed, wind direction, type of precipitation and temperature, on gauge catch ratios were investigated. Wind speed was found to be the most important factor determining the gauge catch and air temperature had a secondary effect when precipitation was classified into snow, mixed and rain. The results of the analysis of gauge catch ratio versus wind speed and temperature on a daily time step are presented for various types of precipitation. Independent checks of the correction equations against the DFIR have been conducted at those Intercomparison stations and a good agreement (difference less than 10%) has been obtained. The use of such adjustment procedures should significantly improve the accuracy and homogeneity of gauge-measured precipitation data over large regions of the former USSR and central Europe. 相似文献
32.
Pb isotope data, major and trace element compositions, fission track and synchrotron X-ray fluorescence analyses are presented
for staurolites from nine pelitic schists in the continental United States to evaluate their potential use in U-Pb geochronology.
Seven U-Pb analyses from Lanzirotti and Hanson (1995) are reexamined with respect to this additional data which was not available
at the time. These data are then compared to 21 new U-Pb analyses of staurolite of varying composition from a variety of localities.
The primary goals of this study are to: (1) evaluate the variability in U and Pb abundance and U/Pb ratio in staurolites of
varying composition; (2) constrain how much of the measured U and Pb is derived from radiogenic solid inclusions such as monazite
and zircon; (3) constrain how much of the measured U and Pb is derived from staurolite itself and evaluate any possible correlation
of U and Pb abundance and U/Pb ratio to major element composition; (4) place preliminary constraints on closure temperature
to Pb diffusion in staurolite; (5) evaluate how meaningful U-Pb ages can better be calculated for the low U/Pb ratio minerals.
In the staurolite fractions analyzed U abundances range from 0.2 to 24.9 ppm, Pb from 0.13 to 2.41 ppm, the 238U/204Pb ratios vary from 135 to 9447, and the 206Pb/204Pb ratios from 23 to 623. For many of the fractions analyzed precise U-Pb ages can be calculated (±10 Ma or better) that appear
to be consistent with available age constraints on the time of peak metamorphism. Mass balance calculations, fission track
analysis, and synchrotron X-ray fluorescence trace element mapping show that although radiogenic inclusions are almost always
present in large staurolite porphyroblasts, it is difficult for inclusions to account for the measured Pb isotopic compositions.
It is also demonstrated that the U-Pb ages calculated for staurolites from Connecticut are at least 20 Ma older than nearby
Rb-Sr muscovite and 40Ar-39Ar hornblende ages. This is consistent with staurolite having a closure temperature to U and Pb diffusion significantly higher
than 500 °C.
Received: 14 July 1995 / Accepted: 16 May 1997 相似文献
33.
A number of significant weaknesses existed in our previous analysis of the changes in the Asian monsoon onset/retreat from coupled model intercomparison project phase 3 (CMIP3) models, including a lack of statistical significance tests, a small number of models analysed, and limited understanding of the causes of model uncertainties. Yet, the latest IPCC report acknowledges limited confidence for projected changes in monsoon onset/retreat. In this study we revisit the topic by expanding the analysis to a large number of CMIP5 models over much longer period and with more diagnoses. Daily 850 hPa wind, volumetric atmospheric precipitable water and rainfall data from 26 CMIP5 models over two sets of 50-year periods are used in this study. The overall model skill in reproducing the temporal and spatial patterns of the monsoon development is similar between CMIP3 and CMIP5 models. They are able to show distinct regional characteristics in the evolutions of Indian summer monsoon (ISM), East Asian summer monsoon (EASM) and West North Pacific summer monsoon (WNPSM). Nevertheless, the averaged onset dates vary significantly among the models. Large uncertainty exists in model-simulated changes in onset/retreat dates and the extent of uncertainty is comparable to that in CMIP3 models. Under global warming, a majority of the models tend to suggest delayed onset for the south Asian monsoon in the eastern part of tropical Indian Ocean and Indochina Peninsula and nearby region, primarily due to weakened tropical circulations and eastward shift of the Walker circulation. The earlier onset over the Arabian Sea and part of the Indian subcontinent in a number of the models are related to an enhanced southwesterly flow in the region. Weak changes in other domains are due to the offsetting results among the models, with some models showing earlier onsets but others showing delayed onsets. Different from the analysis of CMIP3 model results, this analysis highlights the importance of SST warming patterns over both the tropical Pacific and Indian Oceans in affecting the modelling results. The increased atmospheric moisture content offsets some effects of the delayed onset and results in increased rainfall intensity during the active monsoon period. The deficiencies of using rainfall alone in assessing the potential changes of the monsoon system are also shown in this study. 相似文献
34.
Microheterotrophic glucose uptake kinetics (Vmax and [K + Sn] value) and uptake velocities (v) based on natural glucose concentrations (Sn) suggested that glucose concentrations in the Sapelo Island estuary were overestimated by published enzymatic techniques. Glucose oxidase treatment of water samples before glucose measurement yielded results as much as 50% lower than when this step was omitted. Thin layer chromatography shows that glucose must be separated from other carbohydrates (e.g., fructose) which interfere with the glucose assay. 相似文献
35.
Daniel J. Meininger William S. Kinman Susan K. Hanson 《Geostandards and Geoanalytical Research》2023,47(2):457-465
The isotopic composition of cadmium in nuclear debris was measured by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). Mass-independent perturbations due to fission product decay on the isotopes of Cd were observed. Relative fission yields for masses 111, 112, 114 and 116 were determined in each sample of nuclear debris and compared with reported values found in irradiated plutonium and uranium fuels. Mass spectrometry measurements of the valley fission product endpoints are extremely challenging due to the low cumulative fission yields and small amounts of each isotope that are produced. To overcome these challenges, a new purification method for Cd was developed and validated by examination of a number of geological reference materials. 相似文献
36.
37.
Matthew Rioux Samuel Bowring Frank Dudás Richard Hanson 《Contributions to Mineralogy and Petrology》2010,160(5):777-801
U–Pb baddeleyite geochronology has become a major tool for dating mafic rocks, especially dikes associated with Large Igneous
Provinces. However, in many cases, post-crystallization Pb-loss and intergrowth of baddeleyite and zircon limit the precision
and/or accuracy of crystallization ages. We present results from multi-step digestion experiments designed to understand and
reduce these effects. Experiments were carried out on Neoproterozoic baddeleyites with zircon inter- and over-growths from
the Gannakouriep dike swarm, Namibia, and on fragments of a large Paleoproterozoic baddeleyite from the Phalaborwa carbonatite,
South Africa. Multi-step digestion experiments on annealed Phalaborwa baddeleyite were designed to test whether the recently
developed chemical abrasion technique for U–Pb zircon geochronology can be applied to baddeleyite. The experiments generated
complex results—individual digestion steps were both normally and reversely discordant suggesting that U and Pb were decoupled
in the multi-step digestions—and indicate that the current form of multi-step chemical abrasion is not an effective method
for reducing the impact of Pb-loss in baddeleyite. A separate set of experiments on the Gannakouriep baddeleyite focused on
isolating the zircon and baddeleyite components in composite grains. Conventional single-step digestion experiments for this
sample resulted in a discordant suite of analyses with significant scatter attributed to inter- and over-grown zircon and
highlight the difficulty of obtaining precise and accurate ages from composite grains. To isolate the baddeleyite and zircon
in these grains, a two-step HCl–HF chemical abrasion procedure for annealed grains was developed. This technique was successful
at selectively dissolving the baddeleyite and zircon components. Secondary zircon inter- and over-growths of baddeleyite can
occur in samples affected by low-temperature alteration to granulite facies metamorphism, and the new HCl–HF chemical abrasion
procedure provides a method for resolving both the igneous and metamorphic history of these composite grains. 相似文献
38.
39.
Investigations of two incidents in 1972 on the east and west coasts of Britain involving the death of unusually large numbers of Gannets indicated that they were almost certainly unrelated. Concentrations of PCB were much higher in the livers of the birds from the west coast and may possibly have contributed to the death of some or all of them. One of these birds also contained an exceptionally high level of mercury in its liver. 相似文献
40.
Responses of arid and semiarid watersheds to increasing carbon dioxide and climate change as shown by simulation studies 总被引:1,自引:0,他引:1
The atmospheric concentration of carbon dioxide is expected to double in the next century causing increased temperatures and decreasing precipitation in some regions of the U.S. The increase in CO2 will also directly affect stomatal conductance of plants. At the first-order watershed scale, changes in evaporative demand, transpiration, and runoff will also occur. Previous modeling studies of the effect of increased CO2 on the water budgets of watersheds have been single-factor exercises where a single parameter representing stomatal conductance was reduced and the results noted. After showing validation results of the hydrology module, we used a comprehensive ecosystem model to examine the consequences of changes in precipitation, temperature, and CO2-induced plant-function characteristics on small-basin runoff. As a result of the complex interactions and of the compensatory mechanisms simulated by the model, we conclude that for arid and semiarid watersheds of the western United States, there will be little change or an actual decrease in surface runoff because of increased CO2 and climate change. This is due to the decrease in precipitation imposed on the model simulations. Implementing stomatal closure in the model did not increase runoff from the watersheds when temperatures were increased and precipitation decreased. 相似文献