排序方式： 共有16条查询结果，搜索用时 31 毫秒
1.
A. F. Carril C. G. Menéndez A. R. C. Remedio F. Robledo A. S?rensson B. Tencer J.-P. Boulanger M. de Castro D. Jacob H. Le Treut L. Z. X. Li O. Penalba S. Pfeifer M. Rusticucci P. Salio P. Samuelsson E. Sanchez P. Zaninelli 《Climate Dynamics》2012,39(12):2747-2768
The ability of four regional climate models to reproduce the present-day South American climate is examined with emphasis on La Plata Basin. Models were integrated for the period 1991–2000 with initial and lateral boundary conditions from ERA-40 Reanalysis. The ensemble sea level pressure, maximum and minimum temperatures and precipitation are evaluated in terms of seasonal means and extreme indices based on a percentile approach. Dispersion among the individual models and uncertainties when comparing the ensemble mean with different climatologies are also discussed. The ensemble mean is warmer than the observations in South Eastern South America (SESA), especially for minimum winter temperatures with errors increasing in magnitude towards the tails of the distributions. The ensemble mean reproduces the broad spatial pattern of precipitation, but overestimates the convective precipitation in the tropics and the orographic precipitation along the Andes and over the Brazilian Highlands, and underestimates the precipitation near the monsoon core region. The models overestimate the number of wet days and underestimate the daily intensity of rainfall for both seasons suggesting a premature triggering of convection. The skill of models to simulate the intensity of convective precipitation in summer in SESA and the variability associated with heavy precipitation events (the upper quartile daily precipitation) is far from satisfactory. Owing to the sparseness of the observing network, ensemble and observations uncertainties in seasonal means are comparable for some regions and seasons. 相似文献
2.
Spatial and temporal variability of the frequency of extreme daily rainfall regime in the La Plata Basin during the 20th century 总被引：1，自引：1，他引：0
We analyzed trends, interdecadal variability, and the quantification of the changes in the frequency of daily rainfall for two thresholds: 0.1 mm and percentile 75th, using high quality daily series from 52 stations in the La Plata Basin (LPB). We observed increases in the annual frequencies in spatially coherent areas. This coherence was more marked in austral summer, autumn, and spring, during which the greatest increases occurred in southern Brazil, especially during extreme events. In winter, the low and middle basins of the Río Uruguay and Río Paraná showed negative trends, some of which were significant. Interdecadal variability is well defined in the region with more pronounced positive jumps west of the basin between 1950 and 2000. This variability was particularly more marked during periods of extreme rainfall in summer, autumn, and spring, unlike in winter when extreme daily rainfall in the lower Rio Paraná basin decreased by up to 60%. The changes in the past century during extreme rainfall produced modifications in the annual rainfall cycle. The annual cycle of both indices was broader during the last period which is mainly explained by the strong decreases in winter. 相似文献
3.
NIELS B
IE CHRISTENSEN 《Geophysical Prospecting》1990,38(5):545-568
In the linear digital filter theory for calculation of Hankel transforms it is possible to find explicit series expansions for the filter coefficients. A method is presented for optimizing the Hankel filters calculated in this way. For a certain desired accuracy of computation, the sampling density and filter length are minimized by choosing the parameters determining the filter characteristics according to the analytical properties of the input function. A new approach to the calculation of the filter coefficients has been developed for these optimized filters. The length of the filters may be further reduced by introducing a shift in the sampling scheme. 相似文献
4.
Richard J. T. Klein Siri E. H. Eriksen Lars Otto Næss Anne Hammill Thomas M. Tanner Carmenza Robledo Karen L. O’Brien 《Climatic change》2007,84(1):23-44
The need to mainstream adaptation to climate change into development planning and ongoing sectoral decision-making is increasingly
recognised, and several bilateral and multilateral development agencies are starting to take an interest. Over the past years
at least six development agencies have screened their project portfolios, generally with two goals in mind: (1) to ascertain
the extent to which existing development projects already consider climate risks or address vulnerability to climate variability
and change, and (2) to identify opportunities for incorporating climate change explicitly into future projects. As each portfolio
screening was conducted independently, the broader lessons emerging from the screenings have not been systematically analysed.
In this paper we assess the screening activities to date, focusing on both the results and the methods applied. Based on this
assessment we identify opportunities for development agencies to expand their current focus on the links between climate and
development. Most agencies already consider climate change as a real but uncertain threat to future development, but they
have given less thought to how different development patterns might affect vulnerability to climate change. The screenings
undertaken have shown the need to take a comprehensive approach to adaptation and its integration into development planning
and sectoral decision-making, and a number of policy initiatives have been taken to promote such integration. We provide some
initial guidance as to how portfolio screening can be carried out in a way that would allow agencies to assess systematically
the relevance of climate change to their ongoing and planned development projects. 相似文献
5.
Natural Hazards - All decision-making processes are complex and include a high number of variables. Particularly, decisions related to disaster risk reduction despite having an inherent... 相似文献
6.
Bonkosky M Hernández-Delgado EA Sandoz B Robledo IE Norat-Ramírez J Mattei H 《Marine pollution bulletin》2009,58(1):45-54
Human fecal contamination of coral reefs is a major cause of concern. Conventional methods used to monitor microbial water quality cannot be used to discriminate between different fecal pollution sources. Fecal coliforms, enterococci, and human-specific Bacteroides (HF183, HF134), general Bacteroides-Prevotella (GB32), and Clostridium coccoides group (CP) 16S rDNA PCR assays were used to test for the presence of non-point source fecal contamination across the southwestern Puerto Rico shelf. Inshore waters were highly turbid, consistently receiving fecal pollution from variable sources, and showing the highest frequency of positive molecular marker signals. Signals were also detected at offshore waters in compliance with existing microbiological quality regulations. Phylogenetic analysis showed that most isolates were of human fecal origin. The geographic extent of non-point source fecal pollution was large and impacted extensive coral reef systems. This could have deleterious long-term impacts on public health, local fisheries and in tourism potential if not adequately addressed. 相似文献
7.
Since 1979 the Laboratory of Geophysics, University of Aarhus, has been developing a new prospecting tool for obtaining information on the topmost 100 m of the earth. The method is an extension of the conventional geoelectric sounding method, but instead of direct current (DC) the AC-geoelectrical sounding method uses alternating current (AC) with frequencies in the range 100 Hz to 20,000 Hz. The use of alternating current adds an inductive contribution to the ordinary galvanic electric field, thus producing two different sorts of information about the underlying earth structure. These two sets of information are, in many cases, of complementary nature, which enables determination of the ground parameters much more accurately than would otherwise be possible from ordinary DC-geoelectrical soundings. Among these cases is the high resistivity equivalence which appears so frequently in Danish Quaternary deposits. 相似文献
8.
Summary In the first part of this research two models for the luminous efficacy of global solar radiation on horizontal surfaces
and overcast skies have been developed. The first of these models is developed using a method similar to that proposed by
Littlefair (1988). The second model has been obtained from the corresponding illuminance and irradiance models in an, apparently,
new approach to the subject. In the second part of this research, a model for the luminous efficacy of global solar radiation
for intermediate skies and horizontal surfaces is developed from the corresponding illuminance and irradiance models. The
model for intermediate skies is given by the same mathematical function as that of the analogous model for overcast skies,
and only the empirical constants change. In all the cases the only independent variables used are the solar altitude and the
brightness index. The models proposed in the present paper have been statistically tested, and their prediction accuracy compared
with other models available in the scientific literature.
Received June 26, 2000 Revised December 9, 2000 相似文献
9.
Reinhard Madlener Carmenza Robledo Bart Muys Javier T. Blanco Freja 《Climatic change》2006,75(1-2):241-271
Collateral impacts of land use and land-use change and forestry (LULUCF) projects, especially those concerning social and
environmental aspects, have been recognized as important by the Marrakech Accords. The same applies to the necessity of assessing
and, if possible, of quantifying the magnitude of these impacts. This article aims to define, clarify and structure the relevant
social, economic and environmental issues to be addressed and to give examples of indicators that ought to be included in
the planning, design, implementation, monitoring, and ex post evaluation of LULUCF projects. This is being done by providing a conceptual framework for the assessment of the sustainability
of such projects that can be used as a checklist when dealing with concrete projects, and that in principle is applicable
to both Annex I and non-Annex I countries. Finally, a set of recommendations is provided to further develop and promote the
proposed framework. 相似文献
10.
早期碳酸盐胶结作用对砂岩孔隙演化的影响——以塔里木盆地满加尔凹陷志留系砂岩为例 总被引：11，自引：4，他引：7
塔里木盆地满加尔凹陷志留系砂岩为无障壁的潮坪、滨岸及辫状河三角洲沉积的岩屑砂岩和岩屑质石英砂岩,对满北和满东、满南地区志留系砂岩成岩作用序次尤其是碳酸盐胶结的时间、方式和特征、物性的对比研究认为:砂岩中碳酸盐胶结的时间早晚对砂岩孔隙演化具有重要影响,满北地区志留系砂岩发育有大量早期泥晶碳酸盐胶结,显微镜下研究表明这种胶结作用发生在岩石受到充分压实之前,呈基底式胶结,岩石颗粒呈点接触或漂浮状分布于早期碳酸盐胶结物之中,这种胶结作用抑制了岩石后期的压实作用。尽管目前其埋藏达5 000～6 500 m,但其经历的压实作用并不强烈,粒间发育大量早期的碳酸盐胶结物,后来这些胶结物被溶蚀,形成了大量次生孔隙。而在满东和满南地区的志留系砂岩,碳酸盐胶结发生在岩石经过充分压实之后,晚期的碳酸盐胶结物仅分布于岩石经充分压实后的粒间孔隙中,含量较前者低,后期可供溶蚀的碳酸盐比前者少,因而溶蚀形成的次生孔隙有限。因此,尽管满东满南地区志留系埋藏比满北浅（3 700～5 000 m）,碳酸盐胶结物含量也低,也发育晚期碳酸盐胶结物的溶蚀,但岩石的压实作用比满北强,物性比满北低差。这主要与碳酸盐胶结的早晚有关,早期碳酸盐胶结对孔隙演化具有明显控制作用,有利于岩石孔隙的保存,为后来的溶蚀形成次生孔隙提供了条件。 相似文献