排序方式: 共有21条查询结果,搜索用时 31 毫秒
11.
Western North Pacific Tropical Cyclone Intensity Guidance Evaluations Using an Alternative Verification Technique
下载免费PDF全文
![点击此处可从《大气和海洋科学快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
In this study, six intensity forecast guidance techniques from the East China Regional Meteorological Center are verified for the 2008 and 2009 typhoon seasons through an alternative forecast verification technique. This technique is used to verify intensity forecasts if those forecasts call for a typhoon to dissipate or if the real typhoon dissipates. Using a contingency table, skill scores, chance, and probabilities are computed. It is shown that the skill of the six tropical cyclone intensity guidance techniques was highest for the 12-h forecasts, while the lowest skill of all the six models did not occur in 72-h forecasting. For both the 2008 and 2009 seasons, the average probabilities of the forecast intensity having a small error (6 m s-1) tended to decrease steadily. Some of the intensity forecasts had small skill scores, but the associated probabilities of the forecast intensity errors > 15 m s-1 were not the highest. 相似文献
12.
基于多层次可拓评价法的城市燃气管线风险评价研究 总被引:1,自引:0,他引:1
以改进的肯特危险指数评分法对城市燃气管道的危险因素进行识分析,确立了城市燃气管线风险评价指标体系。将传统的可拓学方法改进为多层次可拓评价法,对其中的节域物元、关联度和等级评定程序进行了调整,并建立了相应的准则,对评价对象进行多级综合评价。通过多层次评价,可以获得不同子指标各自的风险等级以及评价对象总体的风险等级。以邯郸市某段燃气管线为例,运用城市燃气管线风险评价模型进行风险评价,得出其多层次风险等级值。通过对比及数据分析,证实了本文方法的可靠性。 相似文献
13.
The GeoPT Proficiency Testing Scheme for Laboratories Routinely Analysing Silicate Rocks: A Review of the Operating Protocol and Proposals for its Modification
下载免费PDF全文
![点击此处可从《Geostandards and Geoanalytical Research》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Michael Thompson Peter C. Webb Philip J. Potts 《Geostandards and Geoanalytical Research》2015,39(4):433-442
The GeoPT proficiency testing programme for geochemical laboratories has been operating for nearly 20 years. This review, based on an analysis of accumulated data and extensive experience, examines whether the protocol followed during this period continues to be appropriate. Possible changes that might be considered for future implementation are examined, in particular the procedures for calculating assigned values, target values, z‐scores and the applicability of dual fitness‐for‐purpose criteria. We conclude that the existing protocol remains largely appropriate and effective, but propose that a single fitness‐for‐purpose criterion be adopted, with an option for laboratories to recalculate their z‐scores if the criterion is inappropriate for their requirements. 相似文献
14.
Ramesh S. V. Teegavarapu 《水文研究》2014,28(11):3789-3808
Spatial interpolation methods used for estimation of missing precipitation data generally under and overestimate the high and low extremes, respectively. This is a major limitation that plagues all spatial interpolation methods as observations from different sites are used in local or global variants of these methods for estimation of missing data. This study proposes bias‐correction methods similar to those used in climate change studies for correcting missing precipitation estimates provided by an optimal spatial interpolation method. The methods are applied to post‐interpolation estimates using quantile mapping, a variant of equi‐distant quantile matching and a new optimal single best estimator (SBE) scheme. The SBE is developed using a mixed‐integer nonlinear programming formulation. K‐fold cross validation of estimation and correction methods is carried out using 15 rain gauges in a temperate climatic region of the U.S. Exhaustive evaluation of bias‐corrected estimates is carried out using several statistical, error, performance and skill score measures. The differences among the bias‐correction methods, the effectiveness of the methods and their limitations are examined. The bias‐correction method based on a variant of equi‐distant quantile matching is recommended. Post‐interpolation bias corrections have preserved the site‐specific summary statistics with minor changes in the magnitudes of error and performance measures. The changes were found to be statistically insignificant based on parametric and nonparametric hypothesis tests. The correction methods provided improved skill scores with minimal changes in magnitudes of several extreme precipitation indices. The bias corrections of estimated data also brought site‐specific serial autocorrelations at different lags and transition states (dry‐to‐dry, dry‐to‐wet, wet‐to‐wet and wet‐to‐dry) close to those from the observed series. Bias corrections of missing data estimates provide better serially complete precipitation time series useful for climate change and variability studies in comparison to uncorrected filled data series. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
15.
In order to improve the reliability of climate reconstruction, especially the climatologies outside the modern observed climate
space, an improved inverse vegetation model using a recent version of BIOME4 has been designed to quantitatively reconstruct
past climates, based on pollen biome scores from the BIOME6000 project. The method has been validated with surface pollen
spectra from Eurasia and Africa, and applied to palaeoclimate reconstruction. At 6 cal ka BP (calendar years), the climate
was generally wetter than today in southern Europe and northern Africa, especially in the summer. Winter temperatures were
higher (1–5°C) than present in southern Scandinavia, northeastern Europe, and southern Africa, but cooler in southern Eurasia
and in tropical Africa, especially in Mediterranean regions. Summer temperatures were generally higher than today in most
of Eurasia and Africa, with a significant warming from ∼3 to 5°C over northwestern and southern Europe, southern Africa, and
eastern Africa. In contrast, summers were 1–3°C cooler than present in the Mediterranean lowlands and in a band from the eastern
Black Sea to Siberia. At 21 cal ka BP, a marked hydrological change can be seen in the tropical zone, where annual precipitation
was ∼200–1,000 mm/year lower than today in equatorial East Africa compared to the present. A robust inverse relationship is
shown between precipitation change and elevation in Africa. This relationship indicates that precipitation likely had an important
role in controlling equilibrium-line altitudes (ELA) changes in the tropics during the LGM period. In Eurasia, hydrological
decreases follow a longitudinal gradient from Europe to Siberia. Winter temperatures were ∼10–17°C lower than today in Eurasia
with a more significant decrease in northern regions. In Africa, winter temperature was ∼10–15°C lower than present in the
south, while it was only reduced by ∼0–3°C in the tropical zone. Comparison of palaeoclimate reconstructions using LGM and
modern CO2 concentrations reveals that the effect of CO2 on pollen-based LGM reconstructions differs by vegetation type. Reconstructions for pollen sites in steppic vegetation in
Europe show warmer winter temperatures under LGM CO2 concentrations than under modern concentrations, and reconstructions for sites in xerophytic woods/scrub in tropical high
altitude regions of Africa are wetter for LGM CO2 concentrations than for modern concentrations, because our reconstructions account for decreased plant water use efficiency. 相似文献
16.
Spatial declustering weights 总被引:1,自引:0,他引:1
G. Bourgault 《Mathematical Geology》1997,29(2):277-290
Because of autocorrelation and spatial clustering, all data within a given dataset have not the same statistical weight for
estimation of global statistics such mean, variance, or quantiles of the population distribution. A measure of redundancy
(or nonredundancy) of any given regionalized random variable Z(uα)within any given set (of size N) of random variables is proposed. It is defined as the ratio of the determinant of the N X Ncorrelation matrix to the determinant of the (N - 1) X (N - 1)correlation matrix excluding random variable Z(uα).This ratio measures the increase in redundancy when adding the random variable Z(uα)to the (N - 1 )remainder. It can be used as declustering weight for any outcome (datum) z(uα). When the redundancy matrix is a kriging covariance matrix, the proposed ratio is the crossvalidation simple kriging variance.
The covariance of the uniform scores of the clustered data is proposed as a redundancy measure robust with respect to data
clustering. 相似文献
17.
表面形貌识别是指用具体的参数表征表面各区段几何形态及属性并最终对不同类型的表面形貌进行识别,表面刻痕识别是其中的一种.以随机过程理论为基础的表面刻痕识别技术可以确切地识别表面形貌的各项特征,其各阶谱矩及统计不变量可以对表面的刻痕以及各向异性进行详细地刻画.区域重力场上的各向异性刻痕主要反映地壳线状变形带,它们常常是区域大地构造单元的边界.本文用重力场研究地壳变形带信息识别方法,将二阶谱矩、统计不变量等参数赋予一定的地质构造含义,并定义了脊形化系数、边界脊形化系数等,从而更详细地表征地壳变形带及大陆构造单元边界信息.理论模型与实际数据试验结果均表明,地壳变形带信息识别方法不但对重力场上地壳变形产生的线形刻痕进行了有效的刻画,而且提取出的刻痕信息,可为大陆构造单元划分提供客观依据. 相似文献
18.
Evaluation of the NMC Regional Ensemble Prediction System During the Beijing 2008 Olympic Games
下载免费PDF全文
![点击此处可从《Acta Meteorologica Sinica》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Based on the B08RDP (Beijing 2008 Olympic Games Mesoscale Ensemble Prediction Research and Development Project) that was launched
by the World Weather Research Programme (WWRP) in 2004, a regional ensemble prediction system (REPS) at a 15-km horizontal
resolution was developed at the National Meteorological Center (NMC) of the China Meteorological Administration (CMA). Supplementing
to the forecasters’ subjective affirmation on the promising performance of the REPS during the 2008 Beijing Olympic Games
(BOG), this paper focuses on the objective verification of the REPS for precipitation forecasts during the BOG period. By
use of a set of advanced probabilistic verification scores, the value of the REPS compared to the quasi-operational global
ensemble prediction system (GEPS) is assessed for a 36-day period (21 July–24 August 2008). The evaluation here involves different
aspects of the REPS and GEPS, including their general forecast skills, specific attributes (reliability and resolution), and
related economic values. The results indicate that the REPS generally performs significantly better for the short-range precipitation
forecasts than the GEPS, and for light to heavy rainfall events, the REPS provides more skillful forecasts for accumulated
6- and 24-h precipitation. By further identifying the performance of the REPS through the attribute-focused measures, it is
found that the advantages of the REPS over the GEPS come from better reliability (smaller biases and better dispersion) and
increased resolution. Also, evaluation of a decision-making score reveals that a much larger group of users benefits from
using the REPS forecasts than using the single model (the control run) forecasts, especially for the heavy rainfall events. 相似文献
19.
The global UK Met office Unified Model (UM) is currently operational at National Centre for Medium Range Weather Forecasting (NCMRWF), the global model named as NCUM. An inter-comparison of two different versions of NCUM has been carried out for simulating the track and intensity of Tropical Cyclones (TCs), which formed over the Bay of Bengal (BoB). For this purpose, two series of numerical experiments named as NCUM25 (New Dynamical core with NCUM N512 resolution) and NCUM17 (ENDGame core with NCUM N768 resolution and upgraded physics and data assimilation scheme) are carried out with seven different initial conditions (ICs) for two TCs. The results suggested that the location, intensity, and vertical structure of the TCs are reasonably well predicted by the NCUM17 over the NCUM25. The Direct Position Error (DPE) and landfall error of TCs are reduced in the NCUM17 in comparison to the NCUM25 for all initial conditions. The mean DPEs and intensity error are reduced by 21–41% and 18–21% in NCUM17 over NCUM25 in both the cases respectively. Improvements in mean landfall position errors are shown to range from 43 to 65% in the NCUM17 as compared to the NCUM25. The mean statistical skill scores for rainfall are considerably improved in NCUM17. 相似文献
20.
Commonly used methods for calculating component scores are reviewed. Means, variances, and the covariance structures of the resulting sets of scores are examined both by calculations based on a large set of electron microprobe analyses of melilite (supplied by D. Velde)and by a survey of recent geological applications of principal component analysis. Most of the procedures used to project raw data into the new vector space yield uncorrelated scores. In exceptions so far encountered, correlations between scores seem to have been occasioned by the use of unstandardized variables with components calculated from a correlation matrix. In a number of cases substantive interpretations of such correlations have been proposed. A different set of correlations results for the same data if scores are computed from standardized variables and components based on the covariance matrix. If unscaled components are rotated by the varimax procedure, the result is a return to the original space. In the work reported here, nevertheless, scores calculated from varimax-rotated scaled vectors are uncorrelated. 相似文献