Dissolved oxygen in the Dead Sea— seasonal changes during the holomictic stage     

Michal Shatkay  David A. Anati  Joel R. Gat 《International Journal of Salt Lake Research》1993,2(2):93-110

Measurements of dissolved oxygen, density and temperature were con ducted in the Dead Sea between August 1987 and December 1989. Oxygen concentrations were found to vary around an average value of 0.8 mlSTP (standard temperature and pressure) per kg. Dissolved oxygen variations were found to reflect both physical processes (a deepening of the epilimnion, a turnover etc.) and chemical processes (oxidation reduction). Transport coefficients for the oxygen exchange across the air/sea interface were found to be generally low compared to expected values based on laboratory experiments; the presence of surface films which inhibit the gas exchange rates under calm weather conditions is suspected. During stormy weather, the exchange rates were considerably higher, suggesting that the entrainment of bubbles was involved in the gas exchange process. Contribution No. 95, Department of Environmental Sciences and Energy Research. The Weizmann Institute of Science  相似文献   

3-D network ray tracing   总被引：15，自引：0，他引：15  

Lud&#;k Klime&#;  Michal Kvasni&#;ka 《Geophysical Journal International》1994,116(3):726-738

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The origin of shallow landslides in Moravia (Czech Republic) in the spring of 2006     

Michal Bíl  Ivo Müller 《Geomorphology》2008,99(1-4):246-253

At the end of March 2006, the Czech Republic (CZ) witnessed a fast thawing of an unusually thick snow cover in conjunction with massive rainfall. Most watercourses suffered floods, and more than 90 shallow landslides occurred in the Moravian region of Eastern CZ, primarily in non-forested areas. This region, geologically part of the Outer Western Carpathians, is prone to landslides because the bedrock is highly erodible Mesozoic and Tertiary flysch.The available meteorological data (depth of snow, water equivalent of the snow, cumulative rainfall, air and soil temperatures) from five local weather stations were used to construct indices quantitatively describing the snow thaw. Among these, the Total Cumulative Precipitation (TCP) combines the amount of water from both thawing snow and rainfall. This concurrence of rain and runoff from snow melt was the decisive factor in triggering the landslides in the spring.The TCP index was applied to data of snow thaw periods for the last 20 years, when no landslides were recorded. This was to establish the safe threshold of TCP without landslides. The calculated safe threshold value for the region is ca. 100 mm of water delivered to the soil during the spring thaw (corresponding to ca. 11 mm day^− 1). In 2006, 10% of the landslides occurred under or at 100 mm of TCP. The upper value of 155 mm covered all of the landslides.  相似文献   

Sensitivity studies with the North Atlantic sigma coordinate Princeton Ocean Model     

Tal Ezer  George L. Mellor 《Dynamics of Atmospheres and Oceans》2000,32(3-4)

The sigma coordinate, Princeton Ocean Model (POM) has been configured for the North Atlantic Ocean between 5°N and 50°N as part of data assimilation, model predictability and intercomparison studies. The model uses a curvilinear orthogonal grid with higher resolution in the western North Atlantic and lower resolution in the eastern North Atlantic. A series of experiments, each one of a 10-year duration, are performed to evaluate the sensitivity of the ocean mean state and variability to model parameters and model configuration; these experiments include open vs. closed boundary conditions, low vs. high resolution grids, and different choices of diffusion and viscosity. The results show that the use of closed boundaries together with near-boundary buffer zones where temperature and salinity are relaxed towards the observed values give less realistic flows, weaker recirculation gyres and less realistic Gulf Stream separation than do open boundary conditions. The experiments show that the sensitivity of the ocean variability in the model to the choice of the Smagorinsky diffusion and viscosity coefficients significantly differs from one region to another and largely depends on other attributes such as the mean position of the Gulf Stream in each simulation. A 50% change in model resolution in the Gulf Stream region has a larger effect on ocean variability than a change of diffusivity by a factor of 10. In areas where either the high or the low resolution models have sufficient resolution, as in the Gulf of Mexico, they are able to produce variability comparable to that observed from altimeter data; elsewhere, model variability is underestimated.  相似文献   

Predicting gully initiation: comparing data mining techniques,analytical hierarchy processes and the topographic threshold     

Tal Svoray  Evgenia Michailov  Avraham Cohen  Lior Rokah  Arnon Sturm 《地球表面变化过程与地形》2012,37(6):607-619

Predicting gully initiation at catchment scale was done previously by integrating a geographical information system (GIS) with physically based models, statistical procedures or with knowledge‐based expert systems. However, the reliability and validity of applying these procedures are still questionable. In this work, a data mining (DM) procedure based on decision trees was applied to identify areas of gully initiation risk. Performance was compared with the analytic hierarchy process (AHP) expert system and with the commonly used topographic threshold (TT) technique. A spatial database was used to test the models, composed of a target variable (presence or absence of initial points) and ten independent environmental, climatic and human‐induced variables. The following findings emerged: using the same input layers, DM provided better predictive ability of gully initiation points than the application of both AHP and TT. The main difference between DM and TT was the very high overestimation inherent in TT. In addition, the minimum slope observed for soil detachment was 2°, whereas in other studies it is 3°. This could be explained by soil resistance, which is substantially lower in agricultural fields, while most studies test unploughed soil. Finally, rainfall intensity events >62.2 mm h^‐1 (for a period of 30 min) were found to have a significant effect on gully initiation. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Effects of water temperature on summer periphyton biomass in shallow lakes: a pan-European mesocosm experiment     

Aldoushy Mahdy  Sabine Hilt  Nur Filiz  Meryem Beklioğlu  Josef Hejzlar  Deniz Özkundakci  Eva Papastergiadou  Ulrike Scharfenberger  Michal Šorf  Kostas Stefanidis  Lea Tuvikene  Priit Zingel  Martin Søndergaard  Erik Jeppesen  Rita Adrian 《Aquatic Sciences - Research Across Boundaries》2015,77(3):499-510

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Iterative Spherical Downward Continuation Applied to Magnetic and Gravitational Data from Satellite   总被引：1，自引：0，他引：1  

Josef Sebera  Michal Šprlák  Pavel Novák  Aleš Bezděk  Miloš Vaľko 《Surveys in Geophysics》2014,35(4):941-958

In the last few decades, satellites have acquired various potential data sets hundreds of kilometers above the Earth’s surface. Conventionally, these global magnetic and gravitational data sets are approximated by using spherical harmonics that allow straightforward work with both fields outside the Earth’s mass. In this article, we present an alternative approach for working with potential data in mass-free space given over a regular coordinate grid on a spherical surface. The algorithm is based on an iterative scheme and the Poisson integral equation for the sphere. With help from the Fourier transform, global potential (magnetic or gravitational) data can efficiently be continued from a mean orbital sphere down to a reference surface without using the spherical harmonics. This is illustrated both with simulated magnetic field data and with real data from the satellite gradiometry mission GOCE. In the case of simulated magnetic data and the downward continuation for 450 km, we have achieved a root mean square at the level of 0.05 nT, while it was <1 E (eotvos) for real GOCE data continued for 250 km. The crucial point is to apply the algorithm twice as a large part of noise can be removed from the input data.  相似文献   

Can the Gulf Stream induce coherent short-term fluctuations in sea level along the US East Coast? A modeling study   总被引：1，自引：1，他引：0  

Tal Ezer 《Ocean Dynamics》2016,66(2):207-220

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On the dynamics and morphology of extensive tidal mudflats: Integrating remote sensing data with an inundation model of Cook Inlet, Alaska     

Tal Ezer  Hua Liu 《Ocean Dynamics》2010,60(5):1307-1318

A new method of integrating satellite remote sensing data and inundation models allows the mapping of extensive tidal mudflats in a sub-Arctic estuary, Cook Inlet (CI), Alaska. The rapid movement of the shorelines in CI due to the large tides (~10 m range) is detected from a series of Landsat imagery taken at different tidal stages, whereas GIS tools are used to identify the water coverage in each satellite image and to extract the coordinates of the shoreline. Then, water level along the shoreline for each satellite image is calculated from the observed water level at Anchorage and the statistics of an inundation model. Several applications of the analysis are demonstrated: 1. studying the dynamics of a tidal bore and the flood/ebb processes, 2. identifying climatic changes in mudflats morphology, and 3. mapping previously unobserved mudflat topographies in order to improve inundation models. The method can be used in other regions to evaluate models and improve predictions of catastrophic floods such as those associated with hurricane storm surges and tsunamis.  相似文献   

Effects of vegetation on channel morphodynamics: results and insights from laboratory experiments   总被引：1，自引：0，他引：1  

Michal Tal  Chris Paola 《地球表面变化过程与地形》2010,35(9):1014-1028

A series of laboratory experiments demonstrates that riparian vegetation can cause a braided channel to self‐organize to, and maintain, a dynamic, single‐thread channel. The initial condition for the experiments was steady‐state braiding in non‐cohesive sand under uniform discharge. From here, an experiment consisted of repeated cycles alternating a short duration high flow with a long duration low flow, and uniform dispersal of alfalfa seeds over the bed at the end of each high flow. Plants established on freshly deposited bars and areas of braidplain that were unoccupied during low flow. The presence of the plants had the effect of progressively focusing the high flow so that a single dominant channel developed. The single‐thread channel self‐adjusted to carry the high flow. Vegetation also slowed the rate of bank erosion. Matching of deposition along the point bar with erosion along the outer bend enabled the channel to develop sinuosity and migrate laterally while suppressing channel splitting and the creation of new channel width. The experimental channels spontaneously reproduced many of the mechanisms by which natural meandering channels migrate and maintain a single dominant channel, in particular bend growth and channel cutoff. In contrast with the braided system, where channel switching is a nearly continuous process, vegetation maintained a coherent channel until wholesale diversion of flow via cutoff and/or avulsion occurred, by which point the previous channel tended to be highly unfavorable for flow. Thus vegetation discouraged the coexistence of multiple channels. Varying discharge was key to allowing expression of feedbacks between the plants and the flow and promoting the transition from braiding to a single‐thread channel that was then dynamically maintained. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献