Discovery of Earth's quasi‐satellite     

Martin Connors  Christian Veillet  Ramon Brasser  Paul Wiegert  Paul Chodas  Seppo Mikkola  Kimmo Innanen 《Meteoritics & planetary science》2004,39(8):1251-1255

Abstract— The newly discovered asteroid 2003 YN₁₀₇ is currently a quasi‐satellite of the Earth, making a satellite‐like orbit of high inclination with apparent period of one year. The term quasi‐satellite is used since these large orbits are not completely closed, but rather perturbed portions of the asteroid's orbit around the Sun. Due to its extremely Earth‐like orbit, this asteroid is influenced by Earth's gravity to remain within 0.1 AU of the Earth for approximately 10 years (1997 to 2006). Prior to this, it had been on a horseshoe orbit closely following Earth's orbit for several hundred years. It will re‐enter such an orbit, and make one final libration of 123 years, after which it will have a close interaction with the Earth and transition to a circulating orbit. Chaotic effects limit our ability to determine the origin or fate of this object.  相似文献   

Call for applications for two Editor-in-Chief positions of Astrophysics and Space Science (Ap&SS)     

Ramon Khanna 《Astrophysics and Space Science》2013,346(1):1-1

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Contributors to the frequency of intense climate disasters in Asia-Pacific countries     

Vinod Thomas  Jose Ramon G. Albert  Cameron Hepburn 《Climatic change》2014,125(3-4):381-398

With record breaking heat waves, dryness, and floods in several parts of the world in recent years the question arises whether and to what extent the hazard of hydrometeorological extreme weather events has changed, and if changes can be attributed to specific causes. The methodology of probabilistic event attribution allows to evaluate such potential changes in the occurence probabilities of particular types of extreme events. We show that such a probabilistic assessment not only provides information on changing hazards in hydrometerological events but also permits statements about multivariate combinations of hydrometeorological variables. Hence attribution studies could be targeted specifically towards relevant impacts in particular sectors, if different suitable multivariate proxies are used. We demonstrate our methodology by using combinations of temperature, precipitation and humidity in the large ensemble of climate simulations within the weather@home project in order to derive impact-relevant quantities such as a seasonal water balance and heat stress imposed on the human body. Finally, we estimate the hazard probabilities of those events in South-East Europe, a region that has recently experienced severe summer dryness (2012) in combination with multiple heat waves.  相似文献   

Fingerprinting TCE in a bedrock aquifer using compound-specific isotope analysis   总被引：1，自引：0，他引：1  

Lojkasek-Lima P  Aravena R  Parker BL  Cherry JA 《Ground water》2012,50(5):754-764

A dual isotope approach based on compound-specific isotope analysis (CSIA) of carbon (C) and chlorine (Cl) was used to identify sources of persistent trichloroethylene (TCE) that caused the shut-down in 1994 of a municipal well in an extensive fractured dolostone aquifer beneath Guelph, Ontario. Several nearby industrial properties have known subsurface TCE contamination; however, only one has created a comprehensive monitoring network in the bedrock. The impacted municipal well and many monitoring wells were sampled for volatile organic compounds (VOCs), inorganic parameters, and CSIA. A wide range in isotope values was observed at the study site. The TCE varies between -35.6‰ and -21.8‰ and from 1.6‰ to 3.2‰ for δ(13) C and δ(37) Cl, respectively. In case of cis-1,2-dichloroethene, the isotope values range between -36.3‰ and -18.9‰ and from 2.4‰ to 4.7‰ for δ(13) C and δ(37) Cl, respectively. The dual isotope approach represented by a plot of δ(13) C vs. δ(37) Cl shows the municipal well samples grouped in a domain clearly separate from all other samples from the property with the comprehensive well network. The CSIA results collected under non-pumping and short-term pumping conditions thus indicate that this particular property, which has been studied intensively for several years, is not a substantial contributor of the TCE presently in the municipal well under non-pumping conditions. This case study demonstrates that CSIA signatures would have been useful much earlier in the quest to examine sources of the TCE in the municipal well if bedrock monitoring wells had been located at several depths beneath each of the potential TCE-contributing properties. Moreover, the CSIA results show that microbial reductive dechlorination of TCE occurs in some parts of the bedrock aquifer. At this site, the use of CSIA for C and Cl in combination with analyses of VOC and redox parameters proved to be important due to the complexity introduced by biodegradation in the complex fractured rock aquifer. It is highly recommended to revisit the study when the municipal well is back into full operation.  相似文献   

Numerical Study of the Neutral Atmospheric Boundary Layer Over Complex Terrain   总被引：1，自引：1，他引：0  

Gilberto?A.?A.?MoreiraEmail author  André?A.?C.?dos?Santos  Carlos?A.?M.?do?Nascimento  Ramon?M.?Valle 《Boundary-Layer Meteorology》2012,143(2):393-407

We evaluate the Reynolds-averaged Navier–Stokes equations available as commercial computational fluid dynamics code for the simulation of a neutral atmospheric boundary layer and attempt to define a proper numerical simulation procedure. Four turbulence models, including two-equation and Reynolds stress models, were evaluated together with two near-wall models. Mesh and map digitization sensitivity tests were also performed. The simulations were compared to experimental field data from the Askervein Hill in Scotland. The results show that the simulations performed with ANSYS CFX 12.1 on a proper mesh and topological map with a Reynolds stress turbulence model provided the best wind-speed predictions when compared to the experimental results.  相似文献   

Shifting level modelling of hydrologic series     

Jose D. Salas  Duane C. Boes 《Advances in water resources》1980,3(2):59-63

The potential of applying shifting level (SL) models to hydrologic processes is discussed in light of observed statistical characteristics of hydrologic data. An SL model and an ARMA (1, 1) model are fitted to an actual hydrologic series. Computer simulation experiments with these models are carried out to compare maximum accumulated deficit and run properties. Results obtained indicate that the mean maximum accumulated deficit, mean longest negative run length, and mean largest negative run sum for both models are similar while there are differences in their corresponding variances.  相似文献   

Estimation of confidence intervals of quantiles for the Weibull distribution     

J.-H. Heo  J. D. Salas  K.-D. Kim 《Stochastic Environmental Research and Risk Assessment (SERRA)》2001,15(4):284-309

 Estimation of confidence limits and intervals for the two- and three-parameter Weibull distributions are presented based on the methods of moment (MOM), probability weighted moments (PWM), and maximum likelihood (ML). The asymptotic variances of the MOM, PWM, and ML quantile estimators are derived as a function of the sample size, return period, and parameters. Such variances can be used for estimating the confidence limits and confidence intervals of the population quantiles. Except for the two-parameter Weibull model, the formulas obtained do not have simple forms but can be evaluated numerically. Simulation experiments were performed to verify the applicability of the derived confidence intervals of quantiles. The results show that overall, the ML method for estimating the confidence limits performs better than the other two methods in terms of bias and mean square error. This is specially so for γ≥0.5 even for small sample sizes (e.g. N=10). However, the drawback of the ML method for determining the confidence limits is that it requires that the shape parameter be bigger than 2. The Weibull model based on the MOM, ML, and PWM estimation methods was applied to fit the distribution of annual 7-day low flows and 6-h maximum annual rainfall data. The results showed that the differences in the estimated quantiles based on the three methods are not large, generally are less than 10%. However, the differences between the confidence limits and confidence intervals obtained by the three estimation methods may be more significant. For instance, for the 7-day low flows the ratio between the estimated confidence interval to the estimated quantile based on ML is about 17% for T≥2 while it is about 30% for estimation based on MOM and PWM methods. In addition, the analysis of the rainfall data using the three-parameter Weibull showed that while ML parameters can be estimated, the corresponding confidence limits and intervals could not be found because the shape parameter was smaller than 2.  相似文献   

Integrated Landslide Susceptibility Analysis and Hazard Assessment in the Principality of Andorra   总被引：9，自引：2，他引：9  

Corominas  Jordi  Copons  Ramon  Vilaplana  Joan Manuel  Altimir  Joan  Amigó  Jordi 《Natural Hazards》2003,30(3):421-435

In the paper we present the procedure for hazard assessment that has been used to prepare the landslide hazard map of the Principality of Andorra at 1:5,000 scale. The main phases of the hazard assessment are discussed. Susceptibility analysis has involved the location of the potential slope failures, and the estimation of both landslide volume and runout distance. In the susceptible areas, landslide magnitude and frequency has been determined in order to produce the Hazard Zoning Map. Data required for hazard assessment have been introduced into a GIS or derived directly from available Digital Terrain Models. Data handling and treatment with the GIS has allowed the performance of the landslide hazard assessment and mapping in a fast and reproducible way.  相似文献   

Rapid development of an unusual peat-accumulating ecosystem in the Chilean Altiplano     

Lisa R EarleBarry G Warner  Ramon Aravena 《Quaternary Research》2003,59(1):2-11

Stratigraphic relationships, radiocarbon dating, sediment and peat characteristics, and rates of peat and carbon accumulation from a soligenous peatland, or “bofedal,” in the Chilean Altiplano shows the peatland to be unusually young, dynamic, and sensitive to environmental changes. The site lies in the National Park Nevado de Tres Cruces in the puna desert grassland at an elevation of 4300 m a.s.l. Eight peat cores were extracted from a 1.75-km transect yielding a maximum of 3.6 m of organic sediment. Organic matter began to accumulate 1700-1100 cal yr B.P. under a progressively arid local climate, after a period when regional climate is believed to have been more humid than at present. Areas of greater relief and better drainage in the valley bottom eventually fostered the growth of a riparian cushion plant community after water flowing down the valley began to diminish. This led to rapid lateral expansion of the riparian peatland communities over open water in topographic depressions at a rate heretofore unprecedented in the peatland literature. It appears that development of the peatland has been encouraged by autoregulation of internal hydrology. The drainage impediment created by organic mass accumulation in lower-relief areas probably reduced the amount of water arriving at the lower reaches of the peatland. These areas have become progressively drier and have since died and oxidized. Through endogenous peat accumulation and a concomitant drainage impediment, the ecosystem has been migrating upstream over the past 50 years.  相似文献   

Nonlinearities, Feedbacks and Critical Thresholds within the Earth's Climate System     

José A. Rial  Roger A. Pielke Sr.  Martin Beniston  Martin Claussen  Josep Canadell  Peter Cox  Hermann Held  Nathalie de Noblet-Ducoudré  Ronald Prinn  James F. Reynolds  José D. Salas 《Climatic change》2004,65(1-2):11-38

The Earth's climate system is highly nonlinear: inputs and outputs are not proportional, change is often episodic and abrupt, rather than slow and gradual, and multiple equilibria are the norm. While this is widely accepted, there is a relatively poor understanding of the different types of nonlinearities, how they manifest under various conditions, and whether they reflect a climate system driven by astronomical forcings, by internal feedbacks, or by a combination of both. In this paper, after a brief tutorial on the basics of climate nonlinearity, we provide a number of illustrative examples and highlight key mechanisms that give rise to nonlinear behavior, address scale and methodological issues, suggest a robust alternative to prediction that is based on using integrated assessments within the framework of vulnerability studies and, lastly, recommend a number of research priorities and the establishment of education programs in Earth Systems Science. It is imperative that the Earth's climate system research community embraces this nonlinear paradigm if we are to move forward in the assessment of the human influence on climate.  相似文献