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941.
942.
Estimation of groundwater evaporation and salt flux from Owens Lake, California, USA 总被引:3,自引:0,他引:3
S. W. Tyler S. Kranz M. B. Parlange J. Albertson G. G. Katul G. F. Cochran B. A. Lyles G. Holder 《Journal of Hydrology》1997,200(1-4):110-135
Groundwater evaporation and subsequent precipitation of soluble salts at Owens Lake in eastern California have created one of the single largest sources of airborne dust in the USA, yet the evaporation and salt flux have not been fully quantified. In this study, we compare eddy correlation, microlysimeters and solute profiling methods to determine their validity and sensitivity in playa environments. These techniques are often used to estimate evaporative losses, yet have not been critically compared at one field site to judge their relative effectiveness and accuracy. Results suggest that eddy correlation methods are the most widely applicable for the variety of conditions found on large playa lakes. Chloride profiling is shown to be highly sensitive to thermal and density-driven fluxes in the near surface and, as a result, appears to underestimate yearly groundwater evaporation. Yearly mean groundwater evaporation from the playa surface estimated from the three study areas was found to range from 88 to 104 mm year−1, whereas mean evaporation from the brine-covered areas was 872 mm year−1. Uncertainties on these mean rates were estimated to be ±25%, based on comparisons between eddy correlation and lysimeter estimates. On a yearly basis, evaporation accounts for approximately 47 × 106 m3 of water loss from the playa surface and open-water areas of the lake. Over the playa area, as much as 7.5 × 108 kg (7.5 × 105 t) of salt are annually concentrated by evaporation at or near the playa surface, much of which appears to be lost during dust storms in area. 相似文献
943.
The identifiability of parameters in a water quality model of the Biebrza River, Poland 总被引:1,自引:0,他引:1
The identifiability of model parameters of a steady state water quality model of the Biebrza River and the resulting variation in model results was examined by applying the Monte Carlo method which combines calibration, identifiability analysis, uncertainty analysis, and sensitivity analysis. The water quality model simulates the steady state concentration profiles of chloride, phosphate, ammonium, and nitrate as a function of distance along a river. The water quality model with the best combination of parameter values simulates the observed concentrations very well. However, the range of possible modelled concentrations obtained for other more or less equally eligible combinations of parameter values is rather wide. This range in model outcomes reflects possible errors in the model parameters. Discrepancies between the range in model outcomes and the validation data set are only caused by errors in model structure, or (measurement) errors in boundary conditions or input variables. In this sense the validation procedure is a test of model capability, where the effects of calibration errors are filtered out. It is concluded that, despite some slight deviations between model outcome and observations, the model is successful in simulating the spatial pattern of nutrient concentrations in the Biebrza River. 相似文献
944.
Jian Zeng Tian-Chang Chen Wei-Bin Han Jun Fan Si-Hua Zheng Akira Hasegawa Shigeki Horiuchij Satoshi Matsumoto 《地震学报(英文版)》1997,10(3):313-320
Based on the single scattering model of coda power spectrum analysis, digital waveform data of 50 events recorded by the real-time
processing system of the Chengdu telemetry network are analyzed to estimate the Q
c values of earth medium beneath the Chengdu telemetry network for several specified frequencies. It is found that the Q
c shows the frequency dependency in the form of Q
c = Q
0
f
n in the range of 1.0 to 20.0Hz. Estimated Q
0 ranges from 60.83 to 178.05, and n is found to be 0.713 to 1.159. The average value of Q
0 and n are 117 and 0.978 respectively. This result indicates the strong frequency dependency of the attenuation of coda waves beneath
the Chengdu telemetry network. Comparing with the results obtained in other regions of the world, it is found that Q
0
−1 value and its change with frequency are similar to those in regions with strong tectonic activity.
This subject is supported by the Ministry of Personnel, China for partly sponsoring. 相似文献
945.
946.
Hydrologic model parameters obtained from regional regression equations are subject to uncertainty. Consequently, hydrologic
model outputs based on the stochastic parameters are random. This paper presents a systematic analysis of uncertainty associated
with the two parameters, N and K, in Nash's IUH model from different regional regression equations. The uncertainty features
associated with N and K are further incorporated to assess the uncertainty of the resulting IUH. Numerical results indicate
that uncertainty of N and K from the regional regression equations are too significant to be ignored. 相似文献
947.
948.
949.
近年来的一些研究表明,由于地震前孕震区地下介质的电性结构的变化,将导致地磁短周期转换函数发生异常变化。通过对地震前后的地磁短周期转换函数的参数的计算、分析和研究,有可能提取出可靠的地震短临前兆异常(曾小苹等,1990)。为了进一步开展对该方法研究工作并使其在我区地震预测预报研究中得到应用,我们使用了静海台的地磁记录资料,分析计算了该台地磁短周期转换函数在地震前后的变化情况,确立了该方法应用天津地区地震预报的短临异常特征及指标,取得了较好的效果。 相似文献
950.
Budd—Chiari综合征的CT评价 总被引:2,自引:0,他引:2
回顾性分析了52例Budd-Chiari综合征的CT表现,CT显示肝尾叶增大50例(96%),肝脏呈低度密度或密度不均,42例(81%)肝静脉未明显,22例(42%)见有肝内侧枝血管,49例(94%)有肝外侧枝血管,作者认为CT检查对Budd-Chiari综合征有较高的诊断价值。 相似文献