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51.
Time-expanded sampling approach for Ensemble Kalman Filter: Experiment assimilation of simulated soundings 
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下载免费PDF全文 In the Ensemble Kalman Filter (EnKF) data assimilation-prediction system, most of the computation time is spent on the prediction
runs of ensemble members. A limited or small ensemble size does reduce the computational cost, but an excessively small ensemble
size usually leads to filter divergence, especially when there are model errors. In order to improve the efficiency of the
EnKF data assimilation-prediction system and prevent it against filter divergence, a time-expanded sampling approach for EnKF
based on the WRF (Weather Research and Forecasting) model is used to assimilate simulated sounding data. The approach samples
a series of perturbed state vectors from N
b member prediction runs not only at the analysis time (as the conventional approach does) but also at equally separated time
levels (time interval is Δt) before and after the analysis time with M times. All the above sampled state vectors are used to construct the ensemble and compute the background covariance for the
analysis, so the ensemble size is increased from N
b to N
b+2M×N
b=(1+2M)×N
b) without increasing the number of prediction runs (it is still N
b). This reduces the computational cost. A series of experiments are conducted to investigate the impact of Δt (the time interval of time-expanded sampling) and M (the maximum sampling times) on the analysis. The results show that if Δt and M are properly selected, the time-expanded sampling approach achieves the similar effect to that from the conventional approach
with an ensemble size of (1+2M)×N
b, but the number of prediction runs is greatly reduced. 相似文献
52.
北极王湾2010年夏季水体营养盐分布及影响因素 总被引：2，自引：1，他引：1
王湾海域位于北极斯瓦尔巴群岛西北侧,其水体特征主要受到北极冰川与大西洋的共同影响。为了研究冰川融水与大西洋水对王湾营养盐分布以及生态系统的影响,在2010年夏季黄河站考察期间,对王湾海水与地表径流进行采样分析,并测定了营养盐和叶绿素a。结果表明:2010年夏季王湾是大西洋水影响较弱的年份,以低温低盐高营养盐的本地变异水为主导。2010年7月王湾水体可以划分为4个水团,表层水(SW)、中层变异水(TIW)、本地变异水(TLW)和大西洋变异水(TAW),其中,表层水与中层变异水营养盐浓度较低,随着深度增加,本地变异水与大西洋变异水营养盐浓度都较高。大西洋变异水主要影响200m以深水柱,其营养盐浓度低于本地变异水影响的底部值,本地变异水中营养盐浓度的增加主要来自于颗粒物中营养盐的再生。表层水主要来源于地表径流与冰川融水,这些淡水输入与浮游植物的初级生产作用共同决定了表层水的营养盐浓度水平及结构。本地变异水中在水深100m上下出现的铵盐高值可能与浮游动物和/或微生物的代谢过程有关。 相似文献
53.
Hazard analysis of seismic submarine slope instability 总被引：1，自引：0，他引：1
Rafael Rodríguez-Ochoa Farrokh Nadim José M. Cepeda Michael A. Hicks Zhongqiang Liu 《Georisk: Assessment and Management of Risk for Engineered Systems and Geohazards》2015,9(3):128-147
To assess the risk associated with a submarine landslide, one must estimate the probability of slope failure and its consequences. This paper proposes a procedure to estimate the probability of earthquake-induced submarine slope failure (hazard) based on probabilistic seismic hazard analyses, ground response analyses and advanced laboratory tests. The outcomes from these analyses are treated in a probabilistic framework, with analytical simulations using mathematical techniques such as the first-order reliability method, Monte Carlo simulation and Bayesian updating. Fragility curves of slope failure during the earthquake (co-seismic) and after the earthquake (post-seismic) were developed in this study, and were shown to provide a clear and well-organized procedure to estimate the annual failure probability of a submarine slope under earthquake loading. 相似文献
54.
时间扩展取样集合卡尔曼滤波同化模拟探空试验研究 总被引：2，自引：0，他引：2
目前,集合卡尔曼滤波同化预报循环系统主要的计算量和时间都花费在样本成员的预报上,小样本数虽能减少计算量,但样本数过少,特别是当有模式误差时,又会导致滤波发散。为了提高集合卡尔曼滤波同化预报循环系统的效率并减轻滤波发散等问题,开展了基于WRF的时间扩展取样集合卡尔曼滤波同化模拟探空的试验研究,以考察其在中尺度模式中的同化效果。预报时对一组样本数为Nb的样本,不仅在分析时刻取样,同时也在分析时刻前和后每间隔Δt时间进行M次取样,即在没增加预报样本数的情况下,增加了分析样本成员数(Nb+2M×Nb),从而在保证不降低分析精度的前提下,也达到减小集合卡尔曼滤波的计算量的要求。通过一系列试验来检验时间扩展取样的时间间隔Δt及在分析时刻前和后最大取样次数M对同化结果的影响。试验结果表明,当选择合适的Δt和M时,时间扩展集合卡尔曼滤波的同化效果非常接近于样本数为(1+2M)×Nb的传统集合卡尔曼滤波效果,具有一定的可行性。 相似文献
55.
高分辨露头层序地层学的研究基础──准层序的识别 总被引：10，自引：2，他引：10
以塔里木盆地西南缘下石炭统和什拉甫组为例，将微相分析及古生态分析应用于准层序研究之中。在此基础之上，分析沉积层序及其内部各体系域、各种界面的沉积特征。同时，根据准层序垂直叠加的特征来寻找沉积层序内部更高级次的旋回，以达到提高沉积层序的分辨率之目的，恢复该地区维宪期多级次古海平面变化特征。强调准层序分析是高分辨露头层序地层学的研究基础。 相似文献
56.
YAN Qinggao JIANG Xiaojun LI Chao ZHOU Limin WANG Zhongqiang Sultan Baig SHER QU Wenjun DU Andao 《《地质学报》英文版》2018,92(6):2098-20119
The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has been widely studied by geologists because of its porphyry-related Pb-Ag-Au polymetallic deposit and geotectonic location, the material sources of this belt are still debate. Whole-rock analyses show that these rocks have high total alkali contents (3.73–11.08wt%), and their aluminum saturation index (ASI) values widely vary from 0.82 to 3.07, which comprise a metaluminous-peraluminous magma series. These rocks are characterized by high K (K2O/Na2O>1) and low Ti and Mg contents; enrichment in large-ion lithophile elements, such as Rb, Ba, K and light rare earth elements; and depletion in high field strength elements, such as Ta, Nb, P, and Ti. These rocks exhibit moderate Eu (Eu/Eu*=0.86–1.04) and Ce (Ce/Ce*=0.63–0.96) anomalies. Their (87Sr/86Sr)i, εNd(t), zircon εHf(t) and δ18O values range from 0.70839 to 0.71013, from ?10.16 to ?12.45, from ?19.6 to ?5.8, and from 5.69‰ to 8.54‰, respectively, and their Nd and Hf two-stage model ages (TDM2) are 1.67–1.86 Ga and 1.27–2.02 Ga, respectively. These data reflect the primary partial melting of Paleoproterozoic to Mesoproterozoic lower crust with minor residual continental lithospheric mantle and supracrustal metasediments. The lithosphere was likely thickened along the southeastern margin of the Tibetan Plateau following the Indian-Asian continent-continent collision (65–41 Ma). During the post-collision phase (36–16 Ma), the transition from a compressional to extensional setting triggered the convective removal of the over-thickened CLM beneath the Yangtze craton, which led to the upwelling of asthenospheric materials. This process created alkali-rich and high-K magma through the partial melting of the thickened lower crust. Magma that carried Cu-Au-Pb-Ag minerals was emplaced by strike-slip motion along the E- to W- or ENE- to WSW-trending tectonically weak zone, finally forming an alkaline porphyry Cu-Au-Pb-Ag polymetallic deposit. 相似文献
57.
正IGCP 630 and its Structures IGCP 630, with its full title of "Permian–Triassic(P–Tr) climatic and environmental extremes and biotic response", is an International Geoscience Program project sponsored by the United Nation Educational, Scientific Cultural Organization(UNESCO) and International Union of Geological Sciences(IUGS). This project was approved in 2014 and ended in 2018, and has applied for one-year 相似文献
58.
基于乡镇尺度的中国25省区人口分布特征及影响因素 总被引：16，自引：2，他引：14
人口空间分布具有典型的尺度特征,精细尺度的人口分布是当前人口地理学研究的热点和难点。乡镇（街道）是中国人口普查数据公开发布的最小行政单元,乡镇级人口密度计算及其分布特征研究能够更客观、精细地刻画中国人口分布的空间格局和态势,为促进中国人口的合理优化布局提供科学依据和决策支持。本文收集处理了2000年中国25个省（直辖市、自治区）的乡镇（街道）级行政边界数据,基于第五次人口普查乡镇（街道）人口统计数据,计算了乡镇级平均人口密度。采用Lorenz曲线、空间分析及样带分析的方法,分析了研究区乡镇（街道）人口分布的疏密结构、空间集聚性、纬向和经向规律。利用相关分析和逐步回归分析,分省探究了地形起伏度、水网密度、路网密度及社会经济发展水平（利用夜间灯光指数表征）等4个因素对于乡镇级人口分布的影响。研究表明：① 乡镇级平均人口密度能够有效区分出县域内部的人口密度高低差异,整体不均衡性高于基于县级平均人口密度的研究结果;② 乡镇（街道）人口分布总体规律是西北稀疏东南密集,同时,东南密中有疏,西北疏中有密;③ 乡镇（街道）人口分布的经纬向规律变异较大,既受中国三级阶梯地貌大势的影响,也受局部微地形及区域中心城市的影响,并和海岸线、交通枢纽及大江大河的分布具有一定的空间耦合性。④ 乡镇级平均人口密度与地形起伏度、水网密度、路网密度及夜间灯光指数等显著相关,省级平均相关系数分别为-0.56、0.28、0.61、0.69。⑤ 在乡镇尺度上,地形条件及区域发展水平对辽、吉、京、津、沪、冀、豫、陕、晋、鲁、皖、苏、湘、鄂、赣、浙、闽、粤、琼等省份的人口分布具有较强的决定作用。⑥ 对于藏、青、蒙、滇、黔等5省或自治区,需要引入更多的自然环境及社会因素来解释其人口分布的特殊规律。本研究扩充了中国人口地理学的研究尺度和维度,并引入了新的定量分析和空间分析方法,所构建的覆盖中国25省（直辖市、自治区）的乡镇（街道）级人口分布科学数据集丰富了中国人口地理学的2000年本底数据资源。 相似文献
59.
Zhongqiang Liu Graham Gilbert Jose Mauricio Cepeda Asgeir Olaf Kydland Lysdahl Luca Piciullo Heidi Hefre Suzanne Lacasse 《地学前缘(英文版)》2021,12(1):385-393
This paper introduces three machine learning(ML)algorithms,the‘ensemble'Random Forest(RF),the‘ensemble'Gradient Boosted Regression Tree(GBRT)and the Multi Layer Perceptron neural network(MLP)and applies them to the spatial modelling of shallow landslides near Kvam in Norway.In the development of the ML models,a total of 11 significant landslide controlling factors were selected.The controlling factors relate to the geomorphology,geology,geo-environment and anthropogenic effects:slope angle,aspect,plan curvature,profile curvature,flow accumulation,flow direction,distance to rivers,water content,saturation,rainfall and distance to roads.It is observed that slope angle was the most significant controlling factor in the ML analyses.The performance of the three ML models was evaluated quantitatively based on the Receiver Operating Characteristic(ROC)analysis.The results show that the‘ensemble'GBRT machine learning model yielded the most promising results for the spatial prediction of shallow landslides,with a 95%probability of landslide detection and 87%prediction efficiency. 相似文献
60.
象山港水体的磷酸盐及其对赤潮的潜在影响 总被引：1，自引：0，他引：1
根据2012年5月和2017年10月在象山港海域的调查结果,研究了象山港磷酸盐的来源、分布和消耗。磷酸盐浓度在两次的调查中均呈现由港顶向湾口逐渐降低的趋势,说明港顶区有较高浓度磷酸盐的输入,可能主要来自生活污水和海水养殖。磷酸盐、硝酸盐和盐度在象山港外湾的分布特征说明长江和钱塘江是外湾水体磷酸盐的一个重要来源;此外,磷酸盐、硝酸盐和盐度在牛鼻山水道和佛渡水道的差异分布说明,陆地径流可能经由佛渡水道向象山港贡献了一部分的磷酸盐。内湾水体的磷酸盐分布受控于内外湾水体混合和浮游植物的同化作用,磷酸盐在水体停留时间较长的内湾发生了明显的消耗,相比于保守混合模型的估算值,磷酸盐在象山港内湾中的净消耗比例在2012年5月和2017年10月分别约为20%和9%。2017年秋季观测到的磷酸盐浓度[（1.88±0.31）μmol/L]与2002-2005年在同季节观测到的结果相比增加超过了50%,N/P值下降明显,这一变化可能会导致象山港内引发藻华的藻类种群发生变化,同时也可能会引发更为严重的赤潮。 相似文献