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41.
42.
Stable isotope values of Costa Rican surface waters 总被引:3,自引:0,他引:3
Stable isotope data of surface waters from the humid tropics in general, and Costa Rica in particular, are scarce. To improve our understanding of the spatial distribution of stable isotopes in surface waters, we measured δ18O and δD in river and lake (n=63) and precipitation (n=3) samples from Costa Rica. We also present data from the IAEA/WMO isotopes in precipitation network as context for our study. Surface water isotope values do not strongly correlate with elevation, stream head elevation, stream length, distance from Caribbean Sea, or estimated mean annual precipitation for the country as a whole. However, the data show distinct regional trends. The δ18O and δD values downwind of mountain ranges are inversely related to the altitude of the ranges the air masses traverse. In the lee of the high Talamanca Range, δ18O values are 6–8‰ lower, while in the lee of the lower Tilarán Range δ18O values are 2–3‰ lower than upwind sites along the Caribbean Slope. An altitude effect of −1.4‰ δ18O/km is present on the Pacific slope of southern Costa Rica, equivalent to a temperature effect of −0.3‰/°C. The Nicoya and Osa Peninsulas have higher values than upwind sites, suggesting input of Pacific-sourced moisture, evaporative enrichment, or decreased condensation temperatures. Elevated and increasing d-excess values inland along the Nicaragua Trough suggest a recycled component may be an important contributor to the water budget. These data provide preliminary stable isotope information for Costa Rica, and will benefit paleoclimatic research in the region. More detailed studies would be beneficial to our understanding of the controls on stable isotope composition of tropical waters. 相似文献
43.
Akihiro Takeuchi Hiroyuki Nagahama 《Physics of the Earth and Planetary Interiors》2002,130(3-4):285-291
Fracturing and frictional sliding of quartz and granite under dry condition generates fractoluminescence, charged particle emission and electromagnetic radiation. Various kinds of experiments indicate that surface charge density on fracture or frictional slip surface of quartz and granite is 10−4 to 10−2 C/m2 which is larger than bound charges induced by the disappearance of piezoelectricity due to the release of stress. Hole and electron trapping centers, which is found in semiconductor devices with the Si–SiO2 system, are causes of surface charging on fracture or frictional slip surface of quartz crystal. The quantity of the surface charge is enough to cause corona discharge that can generate earthquake lights. The mechanism considering the hole and electron trapping centers has a probability to explain why non-piezoelectric minerals or rocks generate electromagnetic phenomena. It can be one of origins of seismo-electromagnetic phenomena (SEP). 相似文献
44.
海阳断裂是胶东半岛NE向牟平 -即墨断裂带东部一条规模较大的断裂 ,尽管晚更新世以来该断裂的地表断错活动总体上已基本停息 ,但东石兰沟段在晚更新世晚期以来仍有断错地表的活动。最后一次断错地表的活动发生在距今 3 7~ 1 2万年 ,但接近 1 2万年。地表破裂长度约6 5km ,活动段长度 8km。地表断错以走滑活动为主 ,可见最大倾滑位移 0 2m ;根据断层擦痕侧伏角推测最大水平位移 1 13m。最后一次断错地表的活动若以距今 1 2万年计算 ,则最大平均倾滑速率为 0 0 17mm/a ;最大平均右旋走滑速率为 0 0 94mm/a。野外观测到该活动段的断错活动表现为突发断错 ,根据地震地表破裂参数、活动段长度与地震的关系 ,估计其最大潜在地震为 6 级 相似文献
45.
46.
Rachid Ait Akbour Jamaâ Douch Mohamed Hamdani Philippe Schmitz 《Comptes Rendus Geoscience》2002,334(13):981-985
To evaluate the risk of contaminant transport by mobile colloids, it is necessary to understand how colloids and associated pollutants behave during their migration through uncontaminated soil or groundwater. In this study, we investigated the influence of aggregation induced by Ca2+ and trace metals (Pb2+, Cu2+) concentrations on the transport of humic-coated kaolinite colloids through a natural quartz sand at pH=4. Adsorbed divalent cations reduce the colloids surface charge and thereby induce aggregation and deposition in porous media. To cite this article: R. Ait Akbour et al., C. R. Geoscience 334 (2002) 981–985. 相似文献
47.
Methodology for construction, calibration and validation of a national hydrological model for Denmark 总被引:13,自引:0,他引:13
Hans Jrgen Henriksen Lars Troldborg Per Nyegaard Torben Obel Sonnenborg Jens Christian Refsgaard Bjarne Madsen 《Journal of Hydrology》2003,280(1-4):52-71
An integrated groundwater/surface water hydrological model with a 1 km2 grid has been constructed for Denmark covering 43,000 km2. The model is composed of a relatively simple root zone component for estimating the net precipitation, a comprehensive three-dimensional groundwater component for estimating recharge to and hydraulic heads in different geological layers, and a river component for streamflow routing and calculating stream–aquifer interaction. The model was constructed on the basis of the MIKE SHE code and by utilising comprehensive national databases on geology, soil, topography, river systems, climate and hydrology. The present paper describes the modelling process for the 7330 km2 island of Sjælland with emphasis on the problems experienced in combining the classical paradigms of groundwater modelling, such as inverse modelling of steady-state conditions, and catchment modelling, focussing on dynamic conditions and discharge simulation. Three model versions with different assumptions on input data and parameter values were required until the performance of the final, according to pre-defined accuracy criteria, model was evaluated as being satisfactory. The paper highlights the methodological issues related to establishment of performance criteria, parameterisation and assessment of parameter values from field data, calibration and validation test schemes. Most of the parameter values were assessed directly from field data, while about 10 ‘free’ parameters were subject to calibration using a combination of inverse steady-state groundwater modelling and manual trial-and-error dynamic groundwater/surface water modelling. Emphasising the importance of tests against independent data, the validation schemes included combinations of split-sample tests (another period) and proxy-basin tests (another area). 相似文献
48.
Scaling effects on modeled surface energy-balance components using the NOAH-OSU land surface model 总被引:3,自引:0,他引:3
As surface exchange processes are highly non-linear and heterogeneous in space and time, it is important to know the appropriate scale for the reasonable prediction of these exchange processes. For example, the explicit representation of surface variability has been vital in predicting mesoscale weather events such as late-afternoon thunderstorms initiated by latent heat exchanges in mid-latitude regions of the continental United States. This study was undertaken to examine the effects of different spatial scales of input data on modeled fluxes, so as to better understand the resolution needed for accurate modeling. A statistical procedure was followed to select two cells from the Southern Great Plains 1997 hydrology experiment region, each 20 km×20 km, representing the most homogeneous and the most heterogeneous surface conditions (based on soil and vegetation) within the study region. The NOAH-OSU (Oregon State University) Land Surface Model (LSM) was employed to estimate surface energy fluxes. Three scales of study (200 m, 2 and 20 km) were considered in order to investigate the impacts of the aggregation of input data, especially soil and vegetation inputs, on the model output. Model results of net radiation and latent, sensible and ground heat fluxes were compared for the three scales. For the heterogeneous area, the model output at the 20-km resolution showed some differences when compared with the 200-m and 2-km resolutions. This was more pronounced in latent heat (12% decrease), sensible heat (22% increase), and ground heat flux (44% increase) estimation than in net radiation. The scaling effects were much less for the relatively homogeneous land area with 5% increase in sensible heat and 4% decrease in ground heat flux estimation. All of the model outputs for the 2- and 20-km resolutions were in close agreement. The results suggested that, for this study region, soils and vegetation input resolution of about 2 km should be chosen for realistic modeling of surface exchange processes. This resolution was sufficient to capture the effects of sub-grid scale heterogeneity, while avoiding the data and computational difficulties associated with higher spatial resolutions. 相似文献
49.
冬春季格陵兰海冰变化与初夏中国气温/降水关系的初步分析 总被引:3,自引:5,他引:3
采用英国Hadley中心GISST海冰面积资料,NCEP/NCAR再分析资料以及中国地面降水和气温资料,运用EOF分解,小波分析和合成分析等方法,初步探讨了格陵兰岛两侧附近冬春季海冰面积变化特征及其与初夏6月中国气温和降水的关系,结果表明,格陵兰岛东西两侧海冰面积呈显著反相变化,并且具有明显的年际和年代际周期性振荡,冬春季格陵兰-寻威海海冰与初夏6月中国长江以北气温(降水)正相关(反相关),与长江以南气温(降水)反相关(正相关),而对于戴维斯海峡-拉布拉多海海冰则具有相反的相关型,大尺度500hPa环流合成分析初步表明,冬春季格陵兰附近海冰面积变化伴随着北极极涡环流和北半球阻塞高压的持续异常,海冰变化可能是影响初夏中国气温和降水的因子之一。 相似文献
50.