Offshore aeolian sediment transport across a human‐modified foredune          下载免费PDF全文

Karl F. Nordstrom  Nancy L. Jackson 《地球表面变化过程与地形》2018,43(1):195-201

Concepts derived from previous studies of offshore winds on natural dunes are evaluated on a dune maintained for shore protection during three offshore wind events. The potential for offshore winds to form a lee‐side eddy on the backshore or transfer sediment from the dune and berm crest to the water are evaluated, as are differences in wind speed and sediment transport on the dune crest, berm crest and a pedestrian access gap. The dune is 18–20 m wide near the base and has a crest 4.5 m above backshore elevation. Two sand‐trapping fences facilitate accretion. Data were obtained from wind vanes on the crest and lee of the dune and anemometers and sand traps placed across the dune, on the beach berm crest and in the access gap. Mean wind direction above the dune crest varied from 11 to 3 deg from shore normal. No persistent recirculation eddy occurred on the 12 deg seaward slope. Wind speed on the berm crest was 85–89% of speed at the dune crest, but rates of sediment transport were 2.27 times greater during the strongest winds, indicating that a wide beach overcomes the transport limitation of a dune barrier. Limited transport on the seaward dune ramp indicates that losses to the water are mostly from the backshore, not the dune. The seaward slope gains sand from the landward slope and dune crest. Sand fences causing accretion on the dune ramp during onshore winds lower the seaward slope and reduce the likelihood of detached flows during offshore winds. Transport rates are higher in access gaps than on the dune crest despite lower wind speeds because of flatter slopes and absence of vegetation. Transport rates across dunes and through gaps can be reduced using vegetation and raised walkover structures. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

The Daily Erosion Project – daily estimates of water runoff,soil detachment,and erosion          下载免费PDF全文

Brian Gelder  Tim Sklenar  David James  Daryl Herzmann  Richard Cruse  Karl Gesch  John Laflen 《地球表面变化过程与地形》2018,43(5):1105-1117

Water runoff and sediment transport from agricultural uplands are substantial threats to water quality and sustained crop production. To improve soil and water resources, farmers, conservationists, and policy‐makers must understand how landforms, soil types, farming practices, and rainfall interact with water runoff and soil erosion processes. To that end, the Iowa Daily Erosion Project (IDEP) was designed and implemented in 2003 to inventory these factors across Iowa in the United States. IDEP utilized the Water Erosion Prediction Project (WEPP) soil erosion model along with radar‐derived precipitation data and government‐provided slope, soil, and management information to produce daily estimates of soil erosion and runoff at the township scale (93 km² [36 mi²]). Improved national databases and evolving remote sensing technology now permit the derivation of slope, soil, and field‐level management inputs for WEPP. These remotely sensed parameters, along with more detailed meteorological data, now drive daily WEPP hillslope soil erosion and water runoff estimates at the small watershed scale, approximately 90 km² (35 mi²), across sections of multiple Midwest states. The revisions constitute a substantial improvement as more realistic field conditions are reflected, more detailed weather data are utilized, hill slope sampling density is an order of magnitude greater, and results are aggregated based on surface hydrology enabling further watershed research and analysis. Considering these improvements and the expansion of the project beyond Iowa it was renamed the Daily Erosion Project (DEP). Statistical and comparative evaluations of soil erosion simulations indicate that the sampling density is adequate and the results are defendable. The modeling framework developed is readily adaptable to other regions given suitable inputs. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Modeling and Fitting of Three-Dimensional Mineral Microstructures by Multinary Random Fields     

Teichmann  Jakob  Menzel  Peter  Heinig  Thomas  van den Boogaart  Karl Gerald 《Mathematical Geosciences》2021,53(5):877-904

Mathematical Geosciences - Modeling a mineral microstructure accurately in three dimensions can render realistic mineralogical patterns which can be used for three-dimensional processing...  相似文献   

The chemical composition including the Rare Earth Elements of the three major glass types of Europe and the Orient used in late antiquity and the Middle Ages     

Karl Hans Wedepohl  Klaus Simon  Andreas Kronz 《Chemie der Erde / Geochemistry》2011,71(3):289-296

Sets of 20 soda ash glasses, 16 soda lime glasses and 23 wood ash glasses mainly from excavations in Europe (additional soda ash glasses from Egypt) were analysed on 61 chemical elements. Average SiO₂ is about 62% in soda glasses and 50% in wood ash glasses. The three groups of glasses contain on average 13% Na₂O, 18% Na₂O and 13% K₂O as fluxes to lower the melting temperature of quartz at their production. The starting materials beside quartz were halophytic plant ash for soda ash glass, trona (Na₃H(CO₃)₂·2H₂O) and lime (clamshells) for soda lime glass and beech ash for wood ash glass. Each of the three major glass types contains specific Rare Earth Element (REE) concentrations mainly contained in quartz and its intergrown minerals. 50 Paleozoic and Mesozoic sandstones from Central Europe represent the quartz composition. The REE pattern of these glasses apparently indicates major compositional stages of the Continental Earth's Crust. The boron to lithium and sodium to potassium ratios as in seawater suggest reactions of materials for soda glass with seawater. Negative Ce anomalies in the three glasses are caused by reactions of quartz with seawater.  相似文献   

Effects of deglaciation on the petrology and eruptive history of the Western Volcanic Zone,Iceland     

Deborah E. Eason  John M. Sinton  Karl Grönvold  Mark D. Kurz 《Bulletin of Volcanology》2015,77(6):1-27

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Application of common reflection angle migration for imaging deformation structures in an inner accretionary wedge,Nankai Trough,Japan     

Kazuya Shiraishi  Masako Robb  Karl Hosgood  Yasuhiro Yamada 《Geophysical Prospecting》2019,67(2):317-330

To better image deformation structures within the inner accretionary wedge of the Nankai Trough, Japan, we apply common reflection angle migration to a legacy two-dimensional seismic data set acquired with a 6 km streamer cable. In this region, many seismic surveys have been conducted to study the seismogenic zone related to plate subduction. However, the details of the accreted sediments beneath the Kumano forearc basin are still unclear due to the poor quality of seismic images caused by multiple reflections, highly attenuated signals, and possibly complex geological structures. Generating common image gathers in the subsurface local angle domain rather than the surface offset domain is more advantageous for imaging geological structures that involve complex wave paths and poor illumination. By applying this method, previously unseen structures are revealed in the thick accreted sediments. The newly imaged geometric features of reflectors, such as the folds in the shallow part of the section and the deep reflectors with stepwise discontinuities, imply deformation structures with multiple thrust faults. The reflections within the deep accreted sediments (approximately 5 km) are mainly mapped to far angles (30°–50°) in the common reflection angles, which correspond to the recorded offset distances greater than 4.5 km. This result indicates that the far offset/angle information is critical to image the deformation structures at depth. The new depth image from the common reflection angle migration provides seismic evidence of multiple thrust faults and their relationship with the megathrust fault that is essential for understanding the structure and evolution of the Nankai Trough seismogenic zone.  相似文献   

A numerical investigation of a moderate coastal storm with intense precipitation     

Da‐Lin Zhang  Karl MacGillivray 《大气与海洋》2013,51(2):161-188

Abstract

In this study, the development of a moderate coastal storm with intense precipitation that occurred during 12–14 February 1993 is examined using a high‐resolution version of the Canadian Regional Finite‐element (RFE) model with more realistic physical representations. It is shown that the improved RFE model predicts well the coastal cyclogenesis events and also the distribution and intensity of heavy mixed precipitation (rain and snow) associated with the storm. It is found that the cyclogenesis takes place in response to the low‐level inshore advection of high‐θ_e air from the maritime boundary layer, and the approach of a mid‐level shortwave trough with a warm pool above that is previously associated with a decaying cyclone upstream. More rapid deepening of the cyclone ensues as intense precipitation falls along the warm and cold fronts near the cyclone centre.

Diagnosis of the control and sensitivity simulations reveals that the low‐level inshore warm advection and the propagation of the stratospheric warm pool contribute more significantly to the surface pressure falls during the incipient stage, whereas the mid‐level shortwave trough plays an important role in the cyclogenesis at later stages. Overall, latent heat release accounts for about 50% of the cyclone's total deepening, in agreement with the presence of a moderate baroclinic environment and the generation of intense precipitation.

The diabatic and kinematic structures near the rain‐snow boundary are examined to gain insight into the influence of melting snow on the cyclogenesis. It is shown that the improved RFE model reproduces well the rain‐snow boundary structures as previously observed. Moreover, a thermally indirect circulation (perturbation) can be seen in the vicinity of the rain‐snow boundary. It is found, however, that melting of snow tends to produce a weak negative or negligible impact on the cyclogenesis, as opposed to previous hypotheses.  相似文献   

Ein Modell zur Bestimmung des Einflusses der klimatischen Bedingungen auf den Wärmehaushalt und das thermische Befinden des Menschen     

Doz. Dr. Karl Höschele 《Theoretical and Applied Climatology》1970,18(1):83-99

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Die Corioliskraft im Anfängerunterricht     

Jung  Karl 《Ocean Dynamics》1951,4(1-2):46-51

Zusammenfassung Es wird eine quantitative Ableitung der Coriolisbeschleunigung auf einer rotierenden Kugel gegeben. Die Rechnungen setzen etwa die Kenntnisse eines Abiturienten voraus und sind so geführt, daß die Coriolisbeschleunigung rein in Erscheinung tritt. Erdabplattung und horizontale Führungskräfte, die mit dem Wesen der Corioliskraft nichts zu tun haben, kommen in der Ableitung nicht vor.

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An introductory mathematical treatment of the Coriolis force

Summary A quantitative derivation of the Coriolis acceleration on a rotating sphere is given which is considered adequate for students who have passed the final examination of a German High School. Computations are presented in a way that demonstrates the Coriolis acceleration without distracting side issues. The earth's oblateness and the horizontal guiding forces not essentially relating to the Coriolis force are not taken into account in this derivation.

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Une introduction dans l'étude de la force de Coriolis

Résumé On donne une dérivation quantitative de l'accélération de Coriolis sur un globe rotatoire. Les calculations nécessaires sont adaptées au savoir d'un bachelier et sont présentées d'une manière que l'accélération de Coriolis est démontrée sans digressions. L'aplatissement de la terre aux pôles et les forces guidantes horizontales qui n'ont pas de rapport essentiel à la nature de l'accélération de Coriolis sont laissés de côté dans cette déduction.

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Meteorologische Faktoren bei der Ausbreitung ultrakurzer Funkwellen     

Prof. Dr. Karl Schneider-Carius 《Pure and Applied Geophysics》1951,20(1):131-137

Zusammenfassung Aus der formalen Aehnlichkeit des Brechungsquotienten (refraction index) für Licht und Ultrakurzwellen (short radio waves) lassen sich gemeinsame Gesichtspunkte für die Ausbreitung des Lichtes und der UK-Wellen (short waves propagation) entwickeln. Anomale Refraktion der Radiowellen insbesondere aussergewöhnliche Reichweite (superrefraction) lassen sich auf diese Weise leicht deuten. Es bestehen hierbei enge Beziehungen zum Aufbau der jeweiligen Grundschicht, wobei erdgebundene Führungen (ground based ducts) auf interne Grenzschichten dicht über der Erdoberfläche, abgehobene Führungen (elevated ducts) auf anomale Refraktion in der Peplopause einer Grundschicht vom Typ A, B oder C zurückzuführen sind. Grundschichten mit einer höher gelegenen Peplopause (Typ D oder E) kommen für eine Führung (duct) nicht mehr in Frage.

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Summary Formal similarity of refraction indices for light and for ultrashort radio waves permits developing common viewpoints of light and of short wave propagation. Thus, anomalous refraction of radio waves, especially superrefraction, is easily explained. With the existing close relations to the structure of the appropriate ground layer, ground based ducts will be traced back to internal limiting layers immediately above the earth's surface, and elevated ducts to anomalous refraction within the peplopause of a Type A, B and/or C ground layer. Ground layers with more elevated peplopause (Types D and/or E) are out of the question for ducts.

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