GRAPES全球集合预报初始条件及模式物理过程不确定性方法研究   总被引：3，自引：0，他引：3       下载免费PDF全文

李晓莉  陈静  刘永柱  彭飞  霍振华 《大气科学学报》2019,42(3):348-359

为描述GRAPES全球模式初始条件的不确定性,基于适合集合预报应用的GRAPES全球奇异向量技术,依据大气初始误差符合正态分布的特征,采用高斯取样奇异向量来构造全球集合预报初始扰动,在此基础上建立了GRAPES全球集合预报系统(GRAPES-GEPS)。利用GRAPES全球同化分析场,对采用初始扰动的GRAPES-GEPS连续试验预报结果进行检验和分析。结果表明:GRAPES-GEPS中高度场、风场及温度场预报的集合离散度能有效快速增加,集合平均均方根误差与集合离散度的关系合理;相对控制预报的均方根误差,集合平均的预报优势在预报中期非常显著。为进一步体现GRAPES-GEPS中模式物理过程的不确定性,发展了模式物理过程倾向随机扰动技术(SPPT)。试验结果表明:SPPT方案的应用有效提高了GRAPES-GEPS在南、北半球和热带地区等压面要素预报的集合离散度,同时一定程度减小了集合平均误差,进而改进了集合平均误差与集合离散度的关系,其中SPPT方案在热带地区的改进最为显著。本文发展的基于奇异向量的初始扰动方法和模式扰动SPPT方案在中国气象局2018年12月业务化运行的GRAPES-GEPS中得到了应用。  相似文献   

藏南邛多江地堑的晚新生代沉积地层及对南北向裂谷形成时代的初步限定   总被引：3，自引：0，他引：3  

哈广浩  吴中海  何林 《地质学报》2018,92(10):2051-2067

邛多江地堑构成了藏南近南北向裂谷带最东侧的错那-沃卡裂谷中段,是由地堑西缘高角度正断层主控的半地堑式断陷盆地。详细的地质、地貌调查表明,该地堑内主要充填有晚新生代以来的多套河湖相、冰碛及冰水沉积地层。河湖相地层底部以黏土和粉砂为主,上部以砾石层为主,向上砾石砾径逐渐变大,顶部为早更新世冲积砾石层;冰碛主要发育于地堑中部山前地带,构成宽缓的冰碛台地或者终碛垄、侧碛堤。地层的测年结果表明,该区主要发育两套晚新生代河湖相地层,早期沉积时代早于5Ma,晚期为晚第四纪;而冰碛及冰水沉积的时代主要为中更新世。综合该区地质地貌、沉积和构造等分析结果表明,早期的河湖相沉积与盆地发生初始裂陷后的主边界正断层发生强烈垂直活动有关,而晚期的河湖相沉积主要形成于盆地后期萎缩过程中,成因可能与中更新世以来的冰川堰塞湖有关。由于邛多江地堑受控于西侧主边界正断层,早期沉积应晚于其初始裂陷时代。因此,进一步综合现有年龄数据资料认为,藏南近南北裂谷的初始裂陷时代应早于5~10Ma,但晚于约15Ma。  相似文献   

Geochemistry of rare-earth elements in thermal waters of Uzon-Geyzernaya hydrothermal system (Kamchatka)     

G.A. Karpov  P.A. Schroeder  A.G. Nikolaeva 《Russian Geology and Geophysics》2018,59(8):925-934

Precisional analyses of the abundances of La, Ce, and major elements in thermal waters and rocks of the Uzon-Geyzernaya volcanotectonic depression, supplemented by published data on a number of modern high-temperature hydrothermal systems of Kamchatka and two other areas of the world, allowed defining genetically important patterns of rare-earth elements (REE) distribution. The La and Ce abundances positively correlate with silica contents both in fresh igneous rocks of the study areas and in the products formed by hydrothermal processes.All studied hydrothermal clays are enriched in La and Ce. The general enrichment trend is similar to the pattern of positive correlation between the La and Ce abundances. Geothermal waters display a strong relationship between REE enrichment and pH. Enhanced REE enrichment trend is observed in thermal waters with abundant SO₄^2 ? and K. The REE versus Cl and B diagrams show two individual fields reflecting the level of acidity-alkalinity of thermal waters. These data demonstrate that La and Ce concentrations in the products of modern hydrothermal systems (in fluids and secondary mineral phases) are governed by wallrock composition, anionic water composition, and pH/Eh-dependent adsorption processes.  相似文献   

Rock-soil slope stability analysis by two-phase random media and finite elements     

《地学前缘(英文版)》2018,9(6):1649-1655

To investigate the strong random nature of the geometric interfaces between soil and rock, a rock-soil slope is considered as a two-phase random medium. A nonlinear translation of a Gaussian field is utilized to simulate the two-phase random media, such that the soil(or rock) volume fraction and the inclination of the soil layer can be examined. The finite element method with random media incorporated as the material properties is used to determine the factor of safety of the rock-soil slope. Monte-Carlo simulations are used to estimate the statistical characteristics of the factor of safety. The failure mode of the rock-soil slope is examined by observing the maximum principal plastic strain at incipient slope failure. It is found that the critical surface of a rock-soil slope is fairly irregular, and it significantly differs from that of a pure soil slope. The factor of safety is sensitive to the soil volume faction, but it is predictable. The average factor of safety could be well predicted by the weighted harmonic average between the strength of soil and rock; the prediction model is practical and simple. Parametric studies on the inclination of the soil layer demonstrate that the most instable scenario occurs when the slope angle is consistent with the inclination of the soil layer.  相似文献   

Spectral-spatial classification of hyperspectral images using wavelet transform and hidden Markov random fields     

Elham Kordi Ghasrodashti  Habibollah Danyali 《国际地球制图》2018,33(8):771-790

This paper proposes a spectral–spatial method for classification of hyperspectral images. The proposed method, called SSC, consists of two steps. In the first step, to overcome the computation complexity, a wavelet-based classifier is designed. In the second step, to enhance the classification accuracy, a novel hidden Markov random field called NHMRF technique in spatial domain is suggested. In NHMRF, we convert two-dimensional energies of traditional hidden Markov random field to three-dimensional energies and then we apply edge preserving regularization terms on each two-dimensional energy of this cube. The class label of each test pixel is fixed based on minimum three-dimensional energy achieved by edge preserving regularization terms. Experimental results show that the classification accuracy of the proposed approach based on three-dimensional energies and edge preserving regularization terms is effectively improved in comparison with the state-of-the-art methods.  相似文献   

Boron geochemistry from some typical Tibetan hydrothermal systems: Origin and isotopic fractionation     

《Applied Geochemistry》2015

The Tibetan plateau is characterized by intense hydrothermal activity and abnormal enrichment of trace elements in geothermal waters. Hydrochemistry and B isotope samples from geothermal waters in Tibet were systematically measured to describe the fractionation mechanisms and provide constraints on potential B reservoirs. B concentrations range from 0.35 to 171.90 mg/L, and isotopic values vary between −16.57 ‰ and +0.52 ‰. Geothermal fields along the Indus-Yarlung Zangbo suture zone and N–S rifts are observed with high B concentrations and temperatures. The similar hydrochemical compositions of high-B geothermal waters with magmatic fluid and consistent modeling of B isotopic compositions with present δ¹¹B values imply that the B in high-B geothermal waters is mainly contributed by magmatic sources, probably through magma degassing. In contrast, geothermal fields in other regions of the Lhasa block have relatively low B concentrations and temperatures. After considering the small fractionation factor and representative indicators of Na/Ca, Cl/HCO₃, Na + K and Si, the conformity between modeling results and the isotopic compositions of host rocks suggests that the B in low-temperature geothermal fields is mainly sourced from host rocks. According to simulated results, the B in some shallow geothermal waters not only originated from mixing of cold groundwater with deep thermal waters, but it was also contributed by equilibration with marine sedimentary rocks with an estimated proportion of 10%. It was anticipated that this study would provide useful insight into the sources and fractionation of B as well as further understanding of the relationships between B-rich salt lakes and geothermal activities in the Tibetan plateau.  相似文献   

Statistical equilibrium and ion cyclotron absorption/emission in strongly magnetized plasmas     

Alexander Y. Potekhin  Dong Lai 《Monthly notices of the Royal Astronomical Society》2007,376(2):793-808

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Global, 30-m resolution continuous fields of tree cover: Landsat-based rescaling of MODIS vegetation continuous fields with lidar-based estimates of error   总被引：1，自引：0，他引：1  

《International Journal of Digital Earth》2013,6(5):427-448

Abstract

We developed a global, 30-m resolution dataset of percent tree cover by rescaling the 250-m MOderate-resolution Imaging Spectroradiometer (MODIS) Vegetation Continuous Fields (VCF) Tree Cover layer using circa- 2000 and 2005 Landsat images, incorporating the MODIS Cropland Layer to improve accuracy in agricultural areas. Resulting Landsat-based estimates maintained consistency with the MODIS VCF in both epochs (RMSE =8.6% in 2000 and 11.9% in 2005), but showed improved accuracy in agricultural areas and increased discrimination of small forest patches. Against lidar measurements, the Landsat-based estimates exhibited accuracy slightly less than that of the MODIS VCF (RMSE=16.8% for MODIS-based vs. 17.4% for Landsat-based estimates), but RMSE of Landsat estimates was 3.3 percentage points lower than that of the MODIS data in an agricultural region. The Landsat data retained the saturation artifact of the MODIS VCF at greater than or equal to 80% tree cover but showed greater potential for removal of errors through calibration to lidar, with post-calibration RMSE of 9.4% compared to 13.5% in MODIS estimates. Provided for free download at the Global Land Cover Facility (GLCF) website (www.landcover.org), the 30-m resolution GLCF tree cover dataset is the highest-resolution multi-temporal depiction of Earth's tree cover available to the Earth science community.  相似文献   

Rainfall–runoff modelling of railway embankment steep slopes     

Asim Krishna Sajjan  Yeboah Gyasi-Agyei  Raj Hari Sharma 《水文科学杂志》2013,58(5):1162-1176

Abstract

A distributed 1D rainfall–runoff model is presented. It consists of the Saint Venant continuity and momentum equations for overland flow and a modified Green-Ampt model for the infiltration on railway embankment steep slopes. The model is applied to adjacent 10-m-wide erosion control experimental plots with different percentages of grass cover. A relationship between the 2-day antecedent rainfall and initial moisture content was established and used to predict the saturated hydraulic conductivity (Ks). Average values of Ks for 0, 50 and 100% grass cover were found to be 0.1, 1.19 and 2.56 mm/h, respectively. For the majority of cases, the model simulated runoff with acceptable accuracy, 68% having Nash-Sutcliffe efficiency (NSE) values above 0.50. The average NSE value varied between 0.60 and 0.80, with 0% grass-covered plots yielding the highest values. As expected, the runoff volume decreased with increasing percentage of grass cover.

Citation Sajjan, A.K., Gyasi-Agyei, Y., and Sharma, R.H., 2013. Rainfall–runoff modelling of railway embankment steep slopes. Hydrological Sciences Journal, 58 (5), 1162–1176.

Editor D. Koutsoyiannis  相似文献   

基于重砂鉴定技术的火山岩锆石精选与测年方法关系探讨     

马慧英  孙海清  罗来  马铁球 《华南地质与矿产》2014,(3):187-193

针对中浅变质沉凝灰岩锆石U-Pb同位素年龄分散幅度较大的现状,在湘中地区碧溪长安组底部凝灰岩几次采集样品测年不成功的情况下再次取样,通过室内重砂样品加工分选等工序,利用立体显微镜和偏光显微镜对锆石进行详细的矿物学特征对比分析,确定样品是否有来自不同时代、不同成因或不同地质背景的锆石。将精选出的锆石进行再次分选,分离成两组样品送往测年,采用LA-ICP-MSU-Pb法测得同沉积期的火山岩岩浆成因锆石年龄751±5 Ma和构造岩浆热事件年龄431.3±4.3 Ma,两组年龄数据与区域地质事实吻合。由此认为对此类样品的锆石进行成因、形态与光学性质等方面的综合分析研究,将混合锆石进行分组,有助于同位素测年数据的有效集中,保证测年数据精度。本文研究表明重砂精细分析鉴定是同位素精准定年的基础。  相似文献