Search results for "UAT"
showing 10 items of 12350 documents
Controlled time integration for the numerical simulation of meteor radar reflections
2016
We model meteoroids entering the Earth[U+05F3]s atmosphere as objects surrounded by non-magnetized plasma, and consider efficient numerical simulation of radar reflections from meteors in the time domain. Instead of the widely used finite difference time domain method (FDTD), we use more generalized finite differences by applying the discrete exterior calculus (DEC) and non-uniform leapfrog-style time discretization. The computational domain is presented by convex polyhedral elements. The convergence of the time integration is accelerated by the exact controllability method. The numerical experiments show that our code is efficiently parallelized. The DEC approach is compared to the volume …
Stochastic Galerkin method for cloud simulation
2018
AbstractWe develop a stochastic Galerkin method for a coupled Navier-Stokes-cloud system that models dynamics of warm clouds. Our goal is to explicitly describe the evolution of uncertainties that arise due to unknown input data, such as model parameters and initial or boundary conditions. The developed stochastic Galerkin method combines the space-time approximation obtained by a suitable finite volume method with a spectral-type approximation based on the generalized polynomial chaos expansion in the stochastic space. The resulting numerical scheme yields a second-order accurate approximation in both space and time and exponential convergence in the stochastic space. Our numerical results…
A geological field trip to the Côte d'Ivoire-Ghana transform margin
1998
Abstract During the Equanaute survey (June 1992), fourteen submersible dives were performed between 4950 and 2250 m water depths across the southern slope of the Cote d'Ivoire-Ghana Marginal Ridge (CIGMR), in the eastern Equatorial Atlantic. The CIGMR, a high-standing topographic marginal ridge along the Cote d'Ivoire-Ghana transform margin, is believed to result from a complex structural evolution due to the specific wrench-related rifting between Western Equatorial Africa and Northeastern Brazil, in Early Cretaceous times. In this paper we report and discuss geological observations made during dives, and sample analyses to resolve the lithology, paleoenvironmental conditions, age and orig…
Land Use Affects Carbon Sources to the Pelagic Food Web in a Small Boreal Lake
2016
Small humic forest lakes often have high contributions of methane-derived carbon in their food webs but little is known about the temporal stability of this carbon pathway and how it responds to environmental changes on longer time scales. We reconstructed past variations in the contribution of methanogenic carbon in the pelagic food web of a small boreal lake in Finland by analyzing the stable carbon isotopic composition (δ13C values) of chitinous fossils of planktivorous invertebrates in sediments from the lake. The δ13C values of zooplankton remains show several marked shifts (approx. 10 ‰), consistent with changes in the proportional contribution of carbon from methane-oxidizing bacteri…
Linking tephrochronology and soil characteristics in the Sila and Nebrodi mountains, Italy
2017
Recent studies have demonstrated that soils formed on pyroclastic ash deposits are much more common in the Mediterranean area than previously assumed. These soils are an important key to understanding past volcanic events and landscape evolution. Chronological information in soils of Quaternary volcanic events, however, remains still poorly understood in southern Italy. Using a multi-method forensic approach, we explore the origin and age of volcanic deposits (soils) in Sicily and Calabria. The geochemical signature of the soil was compared to the chemical fingerprint of the magmas of potential source areas of southern Italian volcanoes. The results indicate that the investigated soils on t…
Downscaling of American National Aeronautics and Space Administration (NASA) daily air temperature in Sicily, Italy, and effects on crop reference ev…
2018
Abstract Air temperature (Ta) is one of the key factors in agro-hydrological studies including estimation of crop reference evapotranspiration (ET0), which is crucial for irrigation water management and sustainability of agro-ecosystem productivity. Because direct measurements of ET0 are difficult, expensive and time consuming, the use of physically based or empirical approaches linked to meteorological information is often preferred. The Prediction of Worldwide Energy Resource project developed by the American National Aeronautics and Space Administration (POWER-NASA) provides daily meteorological information on a 1° latitude by 1° longitude grid. Despite the poor spatial resolution charac…
Unionid shells (Hyriopsis cumingii) record manganese cycling at the sediment-water interface in a shallow eutrophic lake in China (Lake Taihu)
2017
Abstract Aquatic eutrophication is becoming a serious environmental problem throughout the world. The utility of bivalves as bio-filters to improve water quality and reduce algal blooms has been widely acknowledged, but the potential usefulness of bivalve shells as retrospective monitors of eutrophication-induced environmental change has received little attention. Here, we present the first multi-year, high-resolution Mn/Ca shell records of the freshwater mussel, Hyriopsis cumingii (Lea, 1852) from a shallow eutrophic lake (Lake Taihu, China). Mn/Ca shell time-series of the two studied shells exhibit a high degree of synchrony after being placed in a precise temporal context by means of gro…
Quartz grains reveal sedimentary palaeoenvironment and past storm events: A case study from eastern Baltic
2018
Abstract Sediment record collected from the coastal lake serves as a powerful tool for reconstructing changes in palaeoenvironment and understanding the potential signals of past storminess. In this study, we use several proxies from sediment of the Holocene Thermal Maximum at coastal Lake Lilaste, Latvia. We focus on surface texture of quartz grains from the mineral inorganic fraction as indicators of depositional environments. We then use this as a proxy for potential storm transport and combine with information on granulometry, diatom stratigraphy and chronology to answer the question whether flux of quartz grains in the lake originated from the sea or from the land. Analyses in a binocu…
Effects of different boundary conditions and palaeotopographies on the onshore response of tsunamis in a numerical model – A case study from western …
2016
Abstract Hydrodynamic numerical models are essential in modern tsunami hazard assessment. They allow the economical simulation of possible tsunami scenarios for areas at risk and provide reliable and detailed insights into local onshore dynamics. This is especially true when simulations are calibrated with field traces of past tsunami inundation events. Following this approach, the current study focuses on palaeotsunami events indicated by sedimentary and geomorphological field traces in the northern Gulf of Kyparissia (NW Greece). Based on three different digital elevation models (DEM) – reflecting the recent and two palaeotopographies – various tsunami wave constellations according to the…
Understanding volcanoes in the Vanuatu arc
2016
We report the first helium isotope survey of volcanic gases, hot springs and some olivine phenocrysts along the Vanuatu island arc, from Tanna in the south to Vanua Lava in the north. Low CO2 content and low He-3/He-4 ratios in thermal fluids of Epi (4.0 +/- 0.1 R-a), Efate (4.5 +/- 0.1 R-a) and Pentecost (5.3 +/- 0.5 R-a) islands coherently indicate reduced mantle gas leakage and crustal contamination by radiogenic helium on these extinct volcanic systems of the former (Pliocene) arc. Instead, presently active Vanuatu volcanoes display He-3/He-4 and C/He-3 ratios typical of subduction-related volcanic arcs: He-3/He-4 ratios range from 6.4 +/- 0.5 Ra in southernmost Tanna and 7.23 +/- 0.09 …