用TRMM/LIS资料分析长江三角洲地区的闪电活动

统计分析了1998~2004年长江三角洲(长三角)地区由星载闪电成像传感器(LIS)观测的闪电资料，发现了该地区LIS闪电活动的一些时空分布特征:闪电次数的年差异较大，最多年份是最少年份的3倍；7~8月盛夏季节是闪电高发期，闪电次数和日数分别占全年的70%和60%；闪电高发期间的抬升指数(IL)小于-2℃；7~8月闪电主要集中于午后，3~6月则集中在上半夜；上海地区单日LIS闪电次数超过8次时，多伴有强对流天气和短时强降水；长三角地区的闪电活动区主要分布在上海的东部，部分沿江、沿湖地区和浙江的龙门山等山区；水域闪电少于陆地，大城市城区下风方向闪电活动较多，部分雷暴刚入海时有加强的趋势。分析表明:太阳辐射的季节变化和日变化等是造成闪电时间分布的主要原因；地形的动力作用和下垫面的物理特性及其差异是造成气候意义上中小尺度闪电空间分布差异的主要原因。文章对LIS闪电定位资料进行了探测效率订正，根据LIS注视时间计算了闪电密度，并与地基闪电定位资料和多普勒天气雷达资料进行了对比。LIS闪电活动特征的分析，对雷暴预警和防灾减灾有指导意义。     

Analysis of extreme rainfall using the log logistic distribution

Computer-intensive methods are used to examine the fit of the log logistic distribution to annual maxima of Irish rainfall. The characteristics of the L-moment solutions are examined by using the conventional bootstrap on the data and by random sampling within the ellipse of concentration of the parameter estimates. A statistical method of examining uncertainty is provided by the maximum product of spacings solution. Factors derived from random division of an interval are proposed for estimation of short-duration falls for which no data are available.     

Unified scaling theory for distributions of temporal and spatial characteristics in seismology

The paper describes the unified scaling theory for distribution functions of temporal and spatial characteristics in seismology. It is based on the scaling of seismological characteristics calculated for various energy–spatial–temporal intervals. The common mathematical methods for the scaling of distribution functions are developed. The means to test possibility of such scaling are found as well. The relationship between the unified scaling theory and other present scaling approaches is determined. The theory is applied to two characteristics of different seismoactive regions. The first characteristic is the waiting time between earthquakes ΔT, the second one is a new space parameter ΔD_min, which is the minimum distance of a current seismic event to the nearest (in space) neighbor in an energy–spatial–temporal interval. The distribution of the characteristics ΔT and ΔD_min allows estimating the time interval to the next earthquake and the distance of the following earthquake from previous earthquakes. Thus, these characteristics are very important for seismic hazard estimations. Scaling of distributions functions is proven to be successful for ΔD_min in all energy–spatial–temporal intervals and for ΔT with variations of energy/magnitude range. The distribution function of ΔT for various time domains was stable in only 60% of the cases, and near to unstable for spatial variations.     

Kernel estimation as a basic tool for geomorphological data analysis

Kernel estimation, based on the convolution of a probability density function with a set of magnitudes or event dates, provides tuneable smooth pictures of probability density functions and event intensity functions. Such pictures are in several respects superior to those provided by histograms, box plots, cumulative distributions or raw plots. They permit examination of broad features and fine structure, are readily produced with modest computational effort and are essentially free of artefacts arising from binning. Examples are given using data on cirque lengths, limestone pavements, glacier areas and dated flood deposits. The technique deserves widespread use in geomorphology and allied sciences. Copyright © 2007 John Wiley & Sons, Ltd.     

On robustness of large quantile estimates to largest elements of the observation series

The robustness of large quantile estimates of largest elements in a small sample by the methods of moments (MOM), L‐moments (LMM) and maximum likelihood (MLM) was evaluated and compared. Bias (B) and mean square error (MSE) were used to measure the estimation methods performance. Quantiles were estimated by eight two‐parameter probability distributions with the variation coefficient being the shape parameter. The effect of dropping largest elements of the series on large quantile values was assessed for various variation coefficient (C_V)/sample size (n) ‘combinations’ with n = 30 as the basic value. To that end, both the Monte Carlo sampling experiments and an asymptotic approach consisting in distribution truncation were applied. In general, both sampling and asymptotic approaches point to MLM as the most robust method of the three considered, with respect to bias of large quantiles. Comparing the performance of two other methods, the MOM estimates were found to be more robust for small and moderate hydrological samples drawn from distributions with zero lower‐bound than were the LMM estimates. Extending the evaluation to outliers, it was shown that all the above findings remain valid. However, using the MSE variation as a measure of performance, the LMM was found to be the best for most distribution/variation coefficient combinations, whereas MOM was found to be the worst. Moreover, removal of the largest sample element need not result in a loss of estimation efficiency. The gain in accuracy is observed for the heavy‐tailed and log‐normal distributions, being particularly distinctive for LMM. In practice, while dealing with a single sample deprived of its largest element, one should choose the estimation method giving the lowest MSE of large quantiles. For n = 30 and several distribution/variation coefficient combinations, the MLM outperformed the two other methods in this respect and its supremacy grew with sample size, while MOM was usually the worst. Copyright © 2006 John Wiley & Sons, Ltd.     

Abrupt variation in channel width along part of the River Severn,near Shrewsbury,Shropshire, England

The River Severn, near Shrewsbury, Shropshire, England, is formed by the union of the uppermost Severn with the Vyrnwy; both of these major headstreams drain from the Welsh upland. That part of the trunk Severn here under consideration has been under investigation for some years as exemplifying Osage-type underfitness. In the course of the investigation, a census was made of width between banktops on two reaches, and of water surface width on one of these reaches: the difference between the two types of width gives the value of a third type, the width of batter. All three width types produce Poisson distributions of frequency. Width, particularly width between banktops, varies rapidly in the downstream direction. In view of the observed Poisson distributions, transform rather than arithmetic values have been used in difference-of-means tests applied to variation along the channel: cube root transforms are the type selected. Although there is little to choose, on the study reaches, between arithmetic means and Poisson modes, the results obtained do suggest a query about the selection of the most appropriate width values, for instance for the purposes of channel morphology. All types of width are found to vary along the channel far more rapidly than would be expected from mere randomness. Variation in bank strength appears to account for about half the variation in width between banktops. The results obtained for batter width could be applied in the design of a sampling programme designed to identify local difference in bank strength.     

麦哲伦海山区维嘉平顶海山群富钴结壳伴生有用元素空间分布特征

本文对麦哲伦海山区维嘉平顶海山群富钴结壳样品中的伴生有用元素(REE、PGE、W、Mo、Au、Te)的空间分布特征进行了研究。研究表明:富钴结壳伴生有用元素在平面上的分布极不均匀,但多以条带状平行水深等深线分布,也有少数区域表现为斑块状分布,且不同的伴生有用元素的富集区域有所差别;REE和PGE主要在南部和西南部斜坡发育,而W、Mo则主要富集于西北部和东部斜坡,Au集中发育在东南部的海斜坡上,Te的分布呈斑块状富集于各向斜坡。随着水深增加,REE和PGE呈现出由最高含量降低后逐渐升高的变化趋势,W、Mo、Au、Te则随着水深增加含量由低升高,后略有降低,再小幅升高的变化趋势。     

利用MODTRAN 3计算我国太阳直接辐射和散射辐射

根据光的多次散射理论——离散纵标法,利用我国国家一级辐射测站的大气廓线,计算出晴空大气观测波段不同高度上的太阳直接辐射和向下散射辐射。将模式输出的地面辐射值与地面辐射观测资料进行比较,对不同高度的太阳直接辐射和向下散射辐射以及日变化进行了讨论。最终目的是直接由MODTRAN3计算我国辐射空白站的地面辐射值,以弥补我国辐射站稀少,时空分布短缺的不足。