Dipping basement reflectors along volcanic passive margins—new insight using data from the Kerguelen Plateau     

Roland Schlich  Yair Rotstein  Marc Schaming 《地学学报》1993,5(2):157-163

Multichannel seismic reflection data from the Southern Kerguelen Plateau show many dipping basement reflectors associated with volcanic flows. These reflectors are quite similar in their shape to seaward-dipping basement reflectors observed along volcanic passive margins. On the Kerguelen Plateau the sources are updip of the basement reflectors, in the presently extinct and eroded volcanoes. We suggest that the same source/reflector geometry may also apply to the seaward-dipping basement reflectors observed along passive margins. We interpret these reflectors to be the result of volcanism on the passive margin which flowed in all directions into the newly created ocean basin at an early spreading stage.  相似文献   

Using Lightning Data to Better Understand and Predict Flash Floods in the Mediterranean     

C. Price  Y. Yair  A. Mugnai  K. Lagouvardos  M. C. Llasat  S. Michaelides  U. Dayan  S. Dietrich  F. Di Paola  E. Galanti  L. Garrote  N. Harats  D. Katsanos  M. Kohn  V. Kotroni  M. Llasat-Botija  B. Lynn  L. Mediero  E. Morin  K. Nicolaides  S. Rozalis  K. Savvidou  B. Ziv 《Surveys in Geophysics》2011,32(6):733-751

One of the costliest natural hazards around the globe is flash floods, resulting from localized intense convective precipitation over short periods of time. Since intense convective rainfall (especially over the continents) is well correlated with lightning activity in these storms, a European Union FP6 FLASH project was realized from 2006 to 2010, focusing on using lightning observations to better understand and predict convective storms that result in flash floods. As part of the project, 23 case studies of flash floods in the Mediterranean region were examined. For the analysis of these storms, lightning data were used together with rainfall estimates in order to understand the storms?? development and electrification processes. In addition, these case studies were simulated using mesoscale meteorological models to better understand the local and synoptic conditions leading to such intense and damaging storms. As part of this project, tools for short-term predictions (nowcasts) of intense convection across the Mediterranean and Europe, and long-term forecasts (a few days) of the likelihood of intense convection, were developed and employed. The project also focused on educational outreach through a special Web site http://flashproject.org supplying real-time lightning observations, real-time experimental nowcasts, medium-range weather forecasts and educational materials. While flash floods and intense thunderstorms cannot be prevented, long-range regional lightning networks can supply valuable data, in real time, for warning the public, end-users and stakeholders of imminent intense rainfall and possible flash floods.  相似文献   

Benthic foraminiferal Mg/Ca-paleothermometry: a revised core-top calibration     

Caroline H Lear  Yair RosenthalNiall Slowey 《Geochimica et cosmochimica acta》2002,66(19):3375-3387

Core-top samples from different ocean basins have been analyzed to refine our current understanding of the sensitivity of benthic foraminiferal calcite magnesium/calcium (Mg/Ca) to bottom water temperatures (BWT). Benthic foraminifera collected from Hawaii, Little Bahama Bank, Sea of Okhotsk, Gulf of California, NE Atlantic, Ceara Rise, Sierra Leone Rise, the Ontong Java Plateau, and the Southern Ocean covering a temperature range of 0.8 to 18°C were used to revise the Cibicidoides Mg/Ca-temperature calibration. The Mg/Ca-BWT relationship of three common Cibicidoides species is described by an exponential equation: Mg/Ca = 0.867 ± 0.049 exp (0.109 ± 0.007 × BWT) (stated errors are 95% CI). The temperature sensitivity is very similar to a previously published calibration. However, the revised calibration has a significantly different preexponential constant, resulting in different predicted absolute temperatures. We attribute this difference in the preexponential constant to an analytical issue of accuracy. Some genera, notably Uvigerina, show apparently lower temperature sensitivity than others, suggesting that the use of constant offsets to account for vital effects in Mg/Ca may not be appropriate. Downcore Mg/Ca reproducibility, as determined on replicate foraminiferal samples, is typically better than 0.1 mmol mol⁻¹ (2 S.E.). Thus, considering the errors associated with the Cibicidoides calibration and the downcore reproducibility, BWT may be estimated to within ±1°C. Application of the revised core-top Mg/Ca-BWT data to Cenozoic foraminiferal Mg/Ca suggests that seawater Mg/Ca was not more than 35% lower than today in the ice-free ocean at 50 Ma.  相似文献   

A temporal-contextual analysis of urban dynamics using location-based data     

A. Yair Grinberger  Noam Shoval 《International journal of geographical information science》2015,29(11):1969-1987

The dynamics of urban activities in Jerusalem were studied by analyzing a large-scale semantically rich movement dataset. The semantic enrichment process was based on coupling movement trajectories sampled by GPS loggers with contextual data derived from trajectory-based digital activity dairies. Although the utility of such procedures in generating trajectory-specific semantic data was noted before, their application stays limited. In this paper, we promote the utilization of these procedures by demonstrating that they are not only feasible but also important for mobility studies. We discuss the characteristics of the semantic enrichment process and the manner by which it was applied within the large-scale analysis of urban dynamics. This application uncovered a time- and context-dependent array of centers in Jerusalem, resulting in a semantically rich characterization of urban dynamics. Such characterization provides otherwise unobtainable insights crucial for urban analysis. Wider implications for movement studies may be derived, as this application demonstrates how diary-based enrichment approaches hold the potential to advance bridging the semantic gap in mobility research.  相似文献   

Runoff generative process and runoff yield from arid talus mantled slopes   总被引：3，自引：0，他引：3  

A. Yair  H. Lavee 《地球表面变化过程与地形》1976,1(3):235-247

Previous works dealing with the influence of a stone cover on runoff yield showed that runoff, attributed to the sealing effect of the topsoil by raindrops impact, was negatively related to the per cent of stone cover and stone size. These works were conducted on gentle slopes (3–11·5 degree) with a per cent of stone cover generally lower than 50 per cent, and composed of gravels. The present study deals with the runoff yield of steep talus slopes (26–36 degree) whose per cent of stone cover is very high (90–100 per cent), composed of cobbles and boulders. Three stimulated rainstorms were performed at various rainfall. intensities and durations on each one of six plots representative of the North eastern sector of Sinai. Although the contiguous stony cover prevented surface sealing by raindrops impact, runoff developed quite quickly on most slopes, and reached at peak discharge, after approximately ten minutes, up to 56 per cent of the rainfall. Differences between plots, in time lag, peak discharge and other hydrological variables, could be attributed mainly to the properties of the upper stony layer, with stone size as the most influential factor. Contrary to previous works, a positive relationship, was obtained between stone size to runoff yield. The result is explained by the process of water concentration. Each cobble and boulder behaves, on a smaller scale, like a bare rocky surface and yields per unit area water amounts beyond the infiltration rate of the limited uncovered areas. For a given stony cover the effect of water concentration is quicker with the big blocks than with gravels. A series of graphs trying to relate theoretically the relative importance of sealing and water concentration processes in runoff generation, at various conditions of stone cover and stone size, is proposed. The graphs enable to reconcile the results of the present study with those of previous works.  相似文献   

APPLICATIONS OF SPATIAL ANALYSIS TECHNIQUES FOR ASSESSING THE CONTRIBUTION OF CLOUD SEEDING TO RAINFALL IN ISRAEL     

Yair Goldreich 《自然地理学》2013,34(6):573-593

The paper summarizes two decades of fitting existing techniques and developing new spatial methods in order to aid the cloud seeders in proving or disproving the value of deliberate rainfall augmentation in Israel. While the spatial regression and the distance correlation matrix (DISTCORMAT) techniques served to distinguish between deliberate rainfall enhancement and inadvertent urban climate modification, the composite correlation map revealed an increase of rainfall duration and an extension of the rainfall target area. Hydrological parameters were utilized to assess the effect of cloud seeding on water resources. Indirectly, the hydrological evidence supported the positive effect of the cloud seeding. Those findings also suggest that cloud seeding augments the rainfall intensity, but interpretation of the composite correlation map does not support this notion. [Key words: cloud seeding, spatial analysis techniques, DISTCORMAT technique, composite correlation map, multiple regression analysis, hydrological parameters, Israel.]  相似文献   

ELF/VLF signatures of sprite-producing lightning discharges observed during the 2005 EuroSprite campaign     

E. Greenberg  C. Price  Y. Yair  C. Haldoupis  O. Chanrion  T. Neubert 《Journal of Atmospheric and Solar》2009,71(12):1254-1266

During the summer of 2005, transient luminous events were optically imaged from the French Pyrénées as part of the EuroSprite campaign. Simultaneously, extremely low frequency (ELF: 3–3000 Hz) and broadband very low frequency (VLF: 3–30 kHz) data were recorded continuously at two separate receivers in Israel, located about 3300 km from the area of the parent lightning discharges responsible for the generation of sprites. Additionally, narrowband VLF data were collected in Crete, at about 2300 km away from the region of sprites.The motivation for the present study was to identify the signature of the sprite-producing lightning discharges in the ELF and VLF electromagnetic frequency bands, to qualify and compare their parameters, and to study the influence of the thunderstorm-activated region on its overlaying ionosphere. For the 15 sprites analyzed, their causative positive cloud-to-ground (+CG) discharges had peak current intensities between +8 and +130 kA whereas their charge moment changes (CMC) ranged from 500 to 3500 C km. Furthermore, the peak current reported by the Météorage lightning network are well correlated with the amplitudes of the VLF bursts, while showing poor correlation with the CMCs which were estimated using ELF methods.Additionally, more than one +CG was associated with six of the sprites, implying that lightning discharges that produce sprites can sometimes have multiple ground connections separated in time and space. Finally, for a significant number of events (33%) an ELF transient was not associated with sprite occurrence, suggesting that long continuing current of tens of ms may not always be a necessary condition for sprite production, a finding which influences the estimation of the global sprite rate based on Schumann resonance (SR) measurements.  相似文献   

Interspecific Competition between Tetrachthamalus oblitteratus and Tetraclita squamosa     

Yair  Achituv 《Marine Ecology》1981,2(3):241-244

Abstract. Direct evidence for interspecific competition between Tetrachthamalus oblitteratus and Tetraclita squamosa is provided. Tetrachthamalus oblitteratus is smothered and eliminated from the main midlittoral zone by encrusting Tetraclita. The disjunct distribution of Tetrachthamalus can be explained by elimination through competitive exclusion.  相似文献   

Non-linear stochastic galaxy biasing in cosmological simulations     

Rachel S. Somerville  †  Gerard Lemson  Yair Sigad  Avishai Dekel  Guinevere Kauffmann  Simon D. M. White 《Monthly notices of the Royal Astronomical Society》2001,320(3):289-306

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Spatial distribution of surface conditions and runoff generation in small arid watersheds, Zin Valley Badlands, Israel     

Nikolaus J. Kuhn  Aaron Yair   《Geomorphology》2004,57(3-4):183-200

High rill density may be regarded as indicative of frequent and integrated runoff along a drainage network. However, field observations of soil development and rill geometry in small, first-order catchments (0.1 to 1 ha) of the Zin Valley Badlands, northern Negev, Israel, suggest a pattern of partial area contribution and frequent flow discontinuities along hillslopes and channels. Changing soil properties, associated with an increase of slope angle and slope length, appear to be responsible for high infiltration on the slopes, leading to nonuniform runoff generation within small drainage basins. Runoff observation, sprinkling tests, and soil analysis along ridges and sideslopes were carried out to test this hypothesis. The results confirmed that infiltration capacity on the sideslopes is significantly higher than on the ridges. Under current rainfall conditions, only extreme rainfall intensities are sufficient to generate runoff along entire slopes. The discontinuous nature of most runoff events causes erosion on ridges and deposition on slopes, which enhances soil development on the valley sideslopes, creating a positive feedback on infiltration rate and depth. This demonstrates that the links between within-storm rainfall conditions and spatial distribution of soil characteristics have to be incorporated into our understanding of landscape development in badlands.  相似文献