Comparing spatial grain-size trends inferred from textural parameters using percentile statistical parameters and those based on the log-hyperbolic method   总被引：1，自引：0，他引：1  

Jesper Bartholdy  Christian Christiansen 《Sedimentary Geology》2007,202(3):436-452

The Folk&Ward (F&W) and the log-hyperbolic methods are applied to a small - and easy to overlook - number of typical sand sized grain-size distributions from the Danish Wadden Sea. The sand originates from the same source, and the pattern of change in the grain-size distributions is, therefore, exclusively linked to dynamic sorting. In general, the F&W parameters reflect the observed grain-size trends far better than the corresponding log-hyperbolic parameters. The log-hyperbolic “typical log grain size”, ν, is sensitive to changes in skewness and cannot replace mean grain size, Mz, in grain-size trend analysis. The four log-hyperbolic parameters describing dispersion δ, τ^− 1, κ^− 1 and ζ are not able to give an unambiguous picture of spreading trends. The F&W sorting parameter, Sd, can therefore not be replaced by any of the log-hyperbolic parameters in grain-size trend analysis. In skewed grain-size distributions, there seems to be a general defect in the log-hyperbolic approximation of the best represented tail. This makes χ less sensitive to indicate the correct sign of slightly skewed grain-size distributions than Sk. However, when examining trends, the relative change between χ and Sk by and large seems to be the same. The log-hyperbolic peakedness parameter, ξ, is preferable to the F&W peakedness (kurtosis) parameter, Kg, because the latter is hypersensitive to small, insignificant variations in a grain-size distribution. By contrast, the concept of peakedness as defined by ξ, seems to relate more directly to sedimentary environmental conditions. In conclusion, the log-hyperbolic method has both advantages and disadvantages when compared with the F&W method. It is thus suggested that a sensible combination of the two methods could be advantageous to sediment trend analysis.  相似文献   

Changes in Seasonal Patterns of Temperature and Precipitation in China During 1971-2000   总被引：1，自引：0，他引：1  

宋连春 《大气科学进展》2007,24(3):459-473

Many studies have shown evidence for significant changes in surface climate in different regions of the world and during different seasons over the past 100 years. Based on daily temperature and precipitation data from 720 climate stations in China, cluster analysis was used to identify regions in China that have experienced similar changes in the seasonal cycle of temperature and precipitation during the 1971-2000 climate normal period. Differences in 11-day averages of daily mean temperature and total precipitation between the first （1971-1985） and second （1986-2000） halves of the record were analyzed using the Mann- Whitney U test and the global κ-means clustering algorithm. Results show that most parts of China experienced significant increases in temperature between the two periods, especially in winter, although some of this warming may be attributable to the urban heat island effect in large cities. Most of western China experienced more precipitation in 1986-2000, while precipitation decreased in the Yellow River valley. Changes in the summer monsoon were also evident, with decreases in precipitation during the onset and decay phases, and increases during the wettest period.  相似文献   

Temporal and spatial trends of precipitation and river flow in the Yangtze River Basin, 1961–2000     

Tong Jiang  Buda Su  Heike Hartmann 《Geomorphology》2007,85(3-4):143

The suspected impact of climate warming on precipitation distribution is examined in the Yangtze River Basin. Daily precipitation data for 147 meteorological stations from 1961–2000 and monthly discharge data for three stations in the basin have been analyzed for temporal and spatial trends. The methods used include the Mann–Kendall test and simple regression analysis. The results show (1) a significant positive trend in summer precipitation at many stations especially for June and July, with the summer precipitation maxima in the middle and lower Yangtze River basin in the 1990s; (2) a positive trend in rainstorm frequency that is the main contributor to increased summer precipitation in the basin; and (3) a significant positive trend in flood discharges in the middle and lower basin related to the spatial patterns and temporal trends of both precipitation and individual rainstorms in the last 40 years. The rainstorms have aggravated floods in the middle and lower Yangtze River Basin in recent decades. The observed trends in precipitation and rainstorms are possibly caused by variations of atmospheric circulation (weakened summer monsoon) under climate warming.  相似文献   

全球生态系统服务的状况与趋势   总被引：4，自引：0，他引：4  

张永民  赵士洞 《地球科学进展》2007,22(5):515-520

简要介绍了千年生态系统评估（MA）状况与趋势工作组的报告《生态系统与人类福祉：现状与趋势》中的第2部分，即“对生态系统服务的评估”。该部分主要对全球生态系统服务在20世纪末的总体状况，以及它们在20世纪后半叶的主要变化趋势进行了评估。评估结果表明，在MA明确评估的24项服务中，15项处于下降趋势，约占60%；4项处于上升趋势，约占18%；其余5项（约占22%）存在显著的空间或时间差异，即在有些地区（时段）处于上升趋势，而在另外一些地区（时段）处于下降趋势。这些变化主要表现在：①全球谷类作物和牲畜等方面的生态系统服务已经取得了显著的提高，但同时却对淡水资源和调控害虫等方面的服务造成了巨大的损害；② 按照当前的捕捞速度，野生鱼类资源已经无法承受人类的持续捕捞；③ 许多地区的淡水资源已经不能满足人类和生态系统的需求，如果延续当前的水资源利用模式，供需之间的差距将会继续扩大；④ 在对污染物质进行无害化处理、保持养分平衡、调控自然灾害，以及控制害虫、疾病与入侵生物的爆发等方面，许多生态系统的调节服务已经呈现出明显的下降趋势；⑤作为生态系统提供供给服务、调节服务和文化服务的基础条件，全球生态系统的支持服务出现了复杂的变化趋势。  相似文献   

Climatic trends of different intensity heavy precipitation events concentration in China     

XIE Zhiqing  DU Yin  JIANG Aijun  DING Yuguo 《地理学报》2005,15(4):459-466

Based on 740 stations of daily precipitation datasets in China, the precipitation- concentration degree (PCD) and precipitation-concentration period (PCP) of different intensity durative precipitation events were calculated to analyze their statistical characteristics, mainly including spatial and temporal distributions, variations and climatic trends of the two parameters of the durative heavy precipitation events in China. It is proved that these two parameters of heavy rainfall can display the temporal inhomogeneity in the precipitation field. And it is also found that there is a good positive relationship between the precipitation-concentration degree and annual rainfall amount in the Eastern and Central China. This method can be applied in flood assessment and climate change fields.  相似文献   

Stationarity of Monthly Rainfall Series, Since the Middle of the XIXth Century. Application to the Case of Peninsular Spain     

María-Carmen Llasat  Luis Quintas 《Natural Hazards》2004,31(3):613-622

Based on analysis techniques including homogeneity testsand anomalies and trend analysis, a methodology was developed and applied to nine long monthlyrainfall series of the Peninsular Spain (1859–1997). Lying on the basis of a previousspatial regionalization, these series are considered to be representative for this area. Afterstudying the main features of their temporal evolution on a regional scale, results have been comparedto those procured by other studies within the AMHY/FRIEND project of UNESCO for otherMediterranean regions. The conclusions show that there is no significant trendin the series. On the contrary, a common dry period for whole Spain between 1935 and 1955 thatcoincides with a negative anomaly affecting the Western Mediterranean has been found.  相似文献   

亚太旅游市场分析与营销战略创新   总被引：2，自引：0，他引：2  

马勇  周娟 《世界地理研究》2003,12(4):90-95

亚太旅游市场作为世界六大旅游区之一，在世界旅游格局中处于重要地位，同时也是中国客源市场的主体。本文简述了亚太旅游市场的构成及其在世界旅游市场中的地位，就此引出对亚太旅游市场发展趋势及特征的分析，并在此基础上归并出亚太旅游市场营销战略发展的新趋势，旨在为中国进一步开拓亚太旅游市场提供一个清晰的思路。  相似文献   

Use of the census of population to discern trends in the Welsh language: an aggregate analysis     

Gary Higgs  Colin Williams  Danny Dorling 《Area》2004,36(2):187-201

The aim of this paper is to present a preliminary analysis of unitary authority level data from the 2001 census of population on the spatial (and, where available, temporal) patterns in proportions of Welsh speakers in Wales. In so doing we draw attention to the advantages (and limitations) of the census as a source of information on the state of the Welsh language. Although a 2 per cent increase in the percentage of Welsh speakers between 1991 and 2001 has been welcomed, several commentators have drawn attention to the change in the nature of the question asked at the 2001 census which may account for some of this increase. In this paper, we assess what is, and is not, possible to discern from the census, draw attention to other potential sources of information on the language and make some preliminary recommendations for those agencies concerned with monitoring trends in the future, both with regard to the need for more detailed language use surveys and the nature of the question included in subsequent censuses that would permit a more useful comparison of spatial and temporal trends.  相似文献   

波阻抗反演技术研究进展   总被引：14，自引：0，他引：14  

卢占武  韩立国 《世界地质》2002,21(4):372-377

波阻抗是描述地层岩性的重要参数之一，而波阻抗反演是地震反演技术的一个重要分支。笔者介绍了国内外波阻抗反演技术的研究现状，分析了目前波阻抗反演存在的主要问题，对各种反演方法进行了分析，总结出各种方法的特点，并探讨了今后该领域研究的主要内容和研究趋势。  相似文献   

DESERTIFICATION IN CHINA: STATUS, TRENDS, AND STRATEGIES     

Zhu Zhen  Cui Shuhong 《地理学报(英文版)》1995,(3)

boncati0uofDcsendcahoninchhaboenificationisoneofthem0stseriotisenvirorunedlissuesoneafth.TheInteInaonalConedontoC0mbatbeeftifiCationswtinforberl994addressed[4]thadeSenificationislandhardation,resultingfromvariousfaders,indudingdiInaticvariationsandhuInana…  相似文献