Statistical Models for the Solar Flare Interval Distribution in Individual Active Regions     

Yūki Kubo 《Solar physics》2008,248(1):85-98

This article discusses statistical models for the solar flare interval distribution in individual active regions. We analyzed solar flare data in 55 active regions that are listed in the Geosynchronous Operational Environmental Satellite (GOES) soft X-ray flare catalog for the years from 1981 to 2005. We discuss some problems with a conventional procedure to derive probability density functions from any data set and propose a new procedure, which uses the maximum likelihood method and Akaike Information Criterion (AIC) to objectively compare some competing probability density functions. Previous studies of the solar flare interval distribution in individual active regions only dealt with constant or time-dependent Poisson process models, and no other models were discussed. We examine three models – exponential, lognormal, and inverse Gaussian – as competing models for probability density functions in this study. We found that lognormal and inverse Gaussian models are more likely models than the exponential model for the solar flare interval distribution in individual active regions. The possible solar flare mechanisms for the distribution models are briefly mentioned. We also briefly investigated the time dependence of probability density functions of the solar flare interval distribution and found that some active regions show time dependence for lognormal and inverse Gaussian distribution functions. The results suggest that solar flares do not occur randomly in time; rather, solar flare intervals appear to be regulated by solar flare mechanisms. Determining a solar flare interval distribution is an essential step in probabilistic solar flare forecasting methods in space weather research. We briefly mention a probabilistic solar flare forecasting method as an application of a solar flare interval distribution analysis. The application of our distribution analysis to a probabilistic solar flare forecasting method is one of the main objectives of this study.  相似文献   

利用瑞利激光雷达和无线电探空仪观测数据对武汉上空重力波特性的研究   总被引：1，自引：0，他引：1       下载免费PDF全文

吕洪方  易帆 《地球物理学报》2006,49(6):1582-1587

本文利用武汉大学的瑞利激光雷达的瑞利散射回波数据(30～65km)来研究武汉地区上空(30.5°N,114.4°E)重力波的活动规律和统计特性.通过对2003年12月到2005年3月观测的200h数据反演的密度进行处理分析,得到了重力波的一些个例特征,并提取垂直波长为2 km以上的重力波进行统计分析.结果表明,最可几的垂直波长是3～4 km和17～20 km,重力波振幅的月平均值在冬季有较大值,夏季值较小.与武汉2004年无线电探空仪的密度扰动提取到的重力波做比较,发现与瑞利激光雷达得到的重力波振幅的月平均值有很强的相关性,也是冬季值比较大,夏季值比较小.通过无线电探空仪的风场数据,本文还得到了急流的季节变化规律、最大风剪切年变化规律,发现急流和最大风剪切与激光雷达的重力波统计结果有很强的相关性.  相似文献   

Stratified sampling of satellite images with a systematic grid of points   总被引：3，自引：0，他引：3  

F. Javier Gallego 《ISPRS Journal of Photogrammetry and Remote Sensing》2005,59(6):369-376

Sampling satellite images presents some specific characteristics: images overlap and many of them fall partially outside the studied region. A careless sampling may introduce an important bias. This paper illustrates the risk of bias and the efficiency improvements of systematic, pps (probability proportional to size) and stratified sampling.A sampling method is proposed with the following criteria: (a) unbiased estimators are easy to compute; (b) it can be combined with stratification; (c) within each stratum, sampling probability is proportional to the area of the sampling unit; and (d) the geographic distribution of the sample is reasonably homogeneous. Thiessen polygons computed on image centres are sampled through a systematic grid of points. The sampling rates in different strata are tuned by dividing the systematic grid into subgrids or replicates and taking for each stratum a certain number of replicates.The approach is illustrated with an application to the estimation of the geometric accuracy of Image2000, a Landsat ETM+ mosaic of the European Union.  相似文献   

Impacts of Positional Error on Spatial Regression Analysis: A Case Study of Address Locations in Syracuse, New York   总被引：1，自引：0，他引：1  

Daniel A Griffith  Marco Millones  Matthew Vincent  David L Johnson  Andrew Hunt 《Transactions in GIS》2007,11(5):655-679

Positional error is the error produced by the discrepancy between reference and recorded locations. In urban landscapes, locations typically are obtained from global positioning systems or geocoding software. Although these technologies have improved the locational accuracy of georeferenced data, they are not error free. This error affects results of any spatial statistical analysis performed with a georeferenced dataset. In this paper we discuss the properties of positional error in an address matching exercise and the allocation of point locations to census geography units. We focus on the error's spatial structure, and more particularly on impacts of error propagation in spatial regression analysis. For this purpose we use two geocoding sources, we briefly describe the magnitude and the nature of their discrepancies, and we evaluate the consequences that this type of locational error has on a spatial regression analysis of pediatric blood lead data for Syracuse, NY. Our findings include: (1) the confirmation of the recurrence of spatial clustering in positional error at various geographic resolutions; and, (2) the identification of a noticeable but not shockingly large impact from positional error propagation in spatial auto‐binomial regression analysis results for the dataset analyzed.  相似文献   

紫坪铺库区断层分布规律统计分析     

周宏伟  佘云龙  李洪 《工程地质学报》2007,15(2):159-163

定量描述地质构造的分布规律对诸如核废料地质处置、边坡稳定性分析、采矿工程以及水利水电工程都具有十分重要的意义。本文根据紫坪铺水库工程区域地质图,通过提取断层信息的方法,获得了断层分布图。对紫坪铺水利枢纽工程库区内尺度跨越3个数量级、共126条断层进行了统计分析,获得了断层长度-数量间的幂律关系,即N(r)~r-D。并通过分段线性拟合的方法,计算了幂指数的值。发现当断层长度r2.5km时,幂指数D=0.32;而当断层长度r2.5km时,幂指数D=1.58。该幂律关系对推演更小或更大规模断层分布具有重要意义。  相似文献   

Bayesian analysis of groundwater quality in a semi-arid coastal county of south Texas   总被引：1，自引：0，他引：1  

V. Uddameri 《Environmental Geology》2007,51(6):941-951

Bayesian frameworks for comparing water quality information to a pre-specified standard or goal and comparing water quality characteristics among two different entities are presented and illustrated using chloride and total dissolved solids (TDS) measurements obtained in the shallower Chicot and the deeper Evangeline formations of the Gulf coast aquifer underlying Refugio County, TX. The Bayesian approach seeks to present evidence in favor of the competing hypotheses which are weighed equally and unlike classical statistics do not make a decision in favor of one hypothesis. When comparing water quality information to a specified goal, the Bayesian approach addresses the more practical question—given all the information, what is the probability of meeting the goal? Similarly, when comparing the water quality between two entities, the approach simply emphasizes the nature and extent of differences and as such is better suited for evaluative studies. Bayesian analysis indicated that average chloride concentrations in the Evangeline formation was 1.65 times the concentrations in the Chicot formation while the corresponding TDS concentration ratio was close to unity. The probability of identifying water with TDS ≤1,000 g/m³ was extremely low, especially in the more prolific Evangeline formation. The probability of groundwater supplies with mean chloride concentrations ≤500 g/m³ was relatively high in the Chicot formation but very low in the Evangeline formation indicating the possible need for blending groundwater with other sources to meet municipal water quality goals.  相似文献   

Analyse statistique de directions non orientees     

M. Westphal 《Pure and Applied Geophysics》1980,119(1):80-86

Résumé On propose un mode de calcul des directions principales d'un ensemble de directions non orientées et des tests de précision. On propose des applications à l'analyse de nuages de pôles et à la recherche d'intersection de cercles de réaimantation.

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Statistical analysis of non-orientated directions. A computing mode of principal directions of a set of non-orientated directions or lineations and statistical tests are presented. An application to the analysis of a set of poles and for finding the intersection of remagnetisation circles is shown.

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Statistical comparisons of heavy-metal concentrations in river sediments   总被引：5，自引：0，他引：5  

K. S. Murray 《Environmental Geology》1996,27(1):54-58

Statisticalt tests were used to determine lead, copper, and chromium enrichment in sediments from the Lower Branch of the Rouge River in southeast Michigan, USA. Both absolute metal concentrations and ratios of trace metal to conservative metal concentrations were used to compare sampled sites along the Lower Branch of the Rouge River to background sites in the headwaters region. Concentration ratios were used to reduce the effects of certain chemical and physical characteristics on the level of metal contained in a given sediment. Results from the comparison of sample sites to the background reveal metal enrichment at several sites, particularly along the highly urbanized, downstream section of the river. This section of the Lower Branch of the Rouge River exhibits significant lead and copper contamination, as well as measurable chromium enrichment when using either concentrations alone or ratios as methods of comparison. The areas of metal enrichment appear to coincide closely with areas of known anthropogenic activities. Of particular interest, however, is the enrichment of lead and copper at two upstream sites where the statistical tests suggest an anthropogenic source for the enrichment, but where no previously known cultural activities existed. These data prompted a historical search of records, which discovered several abandoned landfills immediately upstream of the metal enrichment sites.  相似文献   

Mapping groundwater quality in the Netherlands   总被引：4，自引：0，他引：4  

Edzer J. Pebesma  J. W. de Kwaadsteniet 《Journal of Hydrology》1997,200(1-4):364-386

Maps of 25 groundwater quality variables were obtained by estimating 4 km × 4 km block median concentrations. Estimates were presented as approximate 95% confidence intervals related to four concentration levels mostly obtained from critical levels for human consumption. These maps were based on measurements from 425 monitoring sites of national and provincial groundwater quality monitoring networks. The estimation procedure was based on a stratification by soil type and land use. Within each soil-land use category, measurements were interpolated. Spatial dependence between measurements and regional differences in mean level were taken into account. Stratification turned out to be essential: no or partial stratification (using either soil type or land use) results in essentially different maps. The effect of monitoring network density was studied by leaving out the 173 monitoring sites of the provincial monitoring networks. Important changes in resulting maps were assigned to loss of information on short-distance variation, as well as loss of location-specific information. For 12 variables, maps of changes in groundwater quality were made by spatial interpolation of short-term predictions calculated for each well screen from time series of yearly measurements over 5–7 years, using a simple regression model for variation over time and taking location-specific time-prediction uncertainties into account.

From a policy point of view, the resulting maps can be used either for quantifying diffuse groundwater contamination and location-specific background concentrations (in order to assist local contamination assessment) or for input and validation of policy supporting regional or national groundwater quality models. The maps can be considered as a translation of point information obtained from the monitoring networks into information on spatial units, the size of which is used in regional groundwater models. The maps enable location-specific network optimization. In general, the maps give little reason for reducing the monitoring network density (wide confidence intervals).  相似文献   

1993年世界气候异常原因及大气对东传型ENSO事件响应的诊断分析   总被引：5，自引：0，他引：5  

井传才  曲维政  李若钝  邹娥梅  于惠苓 《热带气象学报》1995,11(1):57-65

主要用气候统计方法，按不同标准对１９４９－１９９２年影响我国（进入防线）的西太平洋台风资料进行过滤分析。确定台风突然加强的标准，在此基础上对它们进行分类，给出各类的时空分布特点及高低层平均环境场，得出的结论是（１）影响我国的突然加强的台风主要出现在每年７－１０月，并集中的南海中部，东海出现的个例减少。（２）按中心气压和近中心的最大风速变化的先后，突然加强台风可分为三类，第三类与第一、二类高低层的产  相似文献