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651.
652.
Statistical Downscaling of Pattern Projection Using Multi-Model Output Variables as Predictors 下载免费PDF全文
A pattern projection downscaling method is employed to predict monthly station precipitation. The predictand is the monthly precipitation at 1 station in China, 60 stations in Korea, and 8 stations in Thailand. The predictors are multiple variables from the output of operational dynamical models. The hindcast datasets span a period of 21 yr from 1983 to 2003. A downscaled prediction is made for each model separately within a leave-one-out cross-validation framework. The pattern projection method uses a moving window, which scans globally, in order to seek the most optimal predictor for each station. The final forecast is the average of the model downscaled precipitation forecasts using the best predictors and is referred to as DMME. It is found that DMME significantly improves the prediction skill by correcting the erroneous signs of the rainfall anomalies in coarse resolution predictions of general circulation models. The correlation coefficient between the prediction of DMME and the observation in Beijing of China reaches 0.71; the skill is improved to 0.75 for Korea and 0.61 for Thailand. The improvement of the prediction skills for the first two cases is attributed to three steps: coupled pattern selection, optimal predictor selection, and multi-model downscaled precipitation ensemble. For Thailand, we use the single-predictor prediction, which results in a lower prediction skill than the other two cases. This study indicates that the large-scale circulation variables, which are predicted by the current operational dynamical models, if selected well, can be used to make skillful predictions of local precipitation by means of appropriate statistical downscaling. 相似文献
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654.
Recent studies have revealed that the Makeng Fe deposit is a skarn type deposit. However, the skarns in Makeng, occurring primarily between limestone and sandstone, are not typically associated with limestone and plutons. Different periods of intrusions, e.7. Hercynian mafic intrusions and Yanshanian (i.e. early Cretaceous) Dayang–Juzhou granitic intrusion, occurred in the Makeng deposit district. In this study, the formation processes of the skarns and Fe mineralization are constrained by detailed fieldwork, petrology, geochronology, and geochemistry. Skarns and Fe mineralization intersecting the Hercynian mafic intrusions are observed in consecutive specimens from the 106# tunnel. They suggest that the skarn formation and Fe mineralization occurred after the Hercynian mafic intrusions and are related to the later Yanshanian Dayang–Juzhou granitic intrusion. The geochronological characteristics of weakly skarn‐altered diabases, the decreasing nature of Fe contents in altered diabase, and the major element compositions of pyroxenes and garnets also support that Hercynian mafic intrusions are strongly reformed by Yanshanian granitic magmas and the Fe migrated from mafic intrusion was responsible for formation of iron ore. 相似文献
655.
YanYan Yang LianYou Liu XiaoYan Li PeiJun Shi GuoMing Zhang YiYing Xiong YanLi Lyu LanLan Guo Bo Liang MengDi Zhao JiaDong Dai XiYang Zuo XuJiao Han 《Sedimentology》2019,66(2):590-603
Aeolian sand entrainment, saltation and deposition are important and closely related near surface processes. Determining how grains are sorted by wind requires a detailed understanding of how aerodynamic sand transport processes vary within the saltating layer with height above the bed. Grain‐size distribution of sand throughout the saltation layer and, in particular, how the associated flux of different grain size changes with variation in wind velocity, remain unclear. In the present study, a blowdown wind tunnel with a 50 cm thick boundary layer was used to investigate saltating sand grains by analyzing the weight percentage and transport flux of different grain‐size fractions and the mean grain size at different wind velocities. It was found that mean grain size decreases with height above the sand bed before undergoing a reversal. The height of the reversal point ranges from 4 to 40 cm, and increases with wind velocity following a non‐linear relationship. The content of the finer fractions (very fine and fine sand) initially increases above the sand bed and then decreases slightly with height, whereas that of the coarser fractions (medium and coarse sand) exhibits the opposite trend. The content of coarser grains and the mean grain size of sand in the saltation layer increase with wind velocity, indicating erosional selectivity with respect to grains in multi‐sized sand beds; but this size selectivity decreases with increasing wind velocity. The vertical mass flux structure of fine sand and very fine sand does not obey a general exponential decay pattern under strong wind conditions; and the coarser the sand grain, the greater the decrease rate of their transport mass with height. The results of these experiments suggest that the grain‐size distribution of a saltating sand cloud is governed by both wind velocity and height within the near‐surface boundary layer. 相似文献
656.
垃圾堆放场氯代脂肪烃对浅层地下水的污染特征初步分析 总被引:12,自引:2,他引:12
研究区是浅层地下水主要补给区,通过区内地下水监测说明,受垃圾淋滤液影响的地下水中氯代烃高值点主要集中在研究区中部;地下水中氯代烃检出值和检出率有季节性变化特征,与垃圾堆放时间和该井距垃圾场堆放场距离有密切关系,堆放时间越长,离垃圾堆放场越近,检出率、检出值越高;对地下水污染的敏感性和影响氯代烃迁移的机理方面进行了分析。 相似文献
657.
658.
河北平原深层碱性淡水形成的水文地球化学模拟——以保定、沧州地区为例 总被引:4,自引:0,他引:4
以揭示河北平原深层碱性淡水化学形成机制为主要研究目的, 选择河北平原深层碱性淡水发育的保定、沧州地区为典型研究区, 应用水文地球综合分析方法和地下水地球化学模拟技术, 探讨了深层碱性淡水水化学性质、分布规律及形成的自然环境; 依据质量守恒原理建立深层地下水质量平衡反应模型, 研究了从山前至滨海整个水流路径上所发生的水文地球化学作用及水、岩间的质量交换, 从而揭示了深层地下水化学演化规律的内涵及深层碱性淡水水化学形成机制.主要结论是深碱性淡水是由山前补给区HCO3-Ca·Mg水逐步演化而来, 从山前至中部平原, 在地下水环境由开放转为封闭的过程中, 方解石、白云石溶解和沉淀, 钠长石、石膏、岩盐和菱铁矿的溶解, Ca-Na阳离子交换是控制其形成和演化的主要水文地球化学作用. 相似文献
659.
Gaopeng Tang Lianheng Zhao Li Liang Shi Zuo Rui Zhang 《Arabian Journal of Geosciences》2017,10(13):280
Based on a brief review of the existing shear strength reduction (SSR) techniques, the objective function of the comprehensive safety factor for simple homogeneous slopes is established by combining the double SSR technique (considered the shortest pathway of the strength reduction) with the upper bound limit analysis theorem, leading to a strict upper bound on the safety factor. Combining nonlinear sequential quadratic programming (SQP) with the random walk method, the value of the comprehensive safety factor can be optimized, avoiding the trap of a local minimum. Compared with classical examples, the present method is a conservative and effective method for slope stability evaluation. A set of design charts for homogeneous slopes under simple and typical conditions, such as surcharge load, pore water pressure, and seismic loading are produced by the analysis of substantial data, which can eliminate the necessity for iterations when calculating the safety factor. These stability charts are presented in a convenient manner to determine the comprehensive safety factors and corresponding failure patterns under different typical conditions, which might be preferred by engineers for performing the preliminary evaluations of slope safety. Several examples are used to illustrate the application of these stability charts under different conditions. 相似文献
660.
中国沿岸海平面变化原因的探讨 总被引:9,自引:0,他引:9
对中国沿岸的月均海平面的变化原因进行了较为细致的分析,讨论了温、压、降水对中国沿岸海平面的影响。得出渤海是我国月均海平面变化最大的海区;黄海月均海面的变化仅次于渤海;东海更次;南海最小。出现极值的时间自北向南依次滞后。静压效应的影响也是自北而南逐渐变小。月均海面中除包含了8~9年及10多年的长周期变化外,14.0和18.0个月左右的周期对海平面有明显的影响,3年的周期不是一种沿岸传播的波动周期。ElNino对中国沿岸海平面起补偿平衡作用。黑潮的增强使中国沿岸海平面均有明显的抬升。 相似文献