Numerical Study of the Neutral Atmospheric Boundary Layer Over Complex Terrain

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.     

Erratum to Identification of tsunami-induced deposits using numerical modeling and rock magnetism techniques: A study case of the 1755 Lisbon tsunami in Algarve,Portugal: [Physics of the Earth and Planetary Interiors Volume 182, Issues 3–4, Pages 187–198 (October 2010)]

Storm- and tsunami-deposits are generated by similar depositional mechanisms making their discrimination hard to establish using classic sedimentologic methods. Here we propose an original approach to identify tsunami-induced deposits by combining numerical simulation and rock magnetism. To test our method, we investigate the tsunami deposit of the Boca do Rio estuary generated by the 1755 earthquake in Lisbon which is well described in the literature. We first test the 1755 tsunami scenario using a numerical inundation model to provide physical parameters for the tsunami wave. Then we use concentration (MS, SIRM) and grain size (χ_ARM, ARM, B1/2, ARM/SIRM) sensitive magnetic proxies coupled with SEM microscopy to unravel the magnetic mineralogy of the tsunami-induced deposit and its associated depositional mechanisms. In order to study the connection between the tsunami deposit and the different sedimentologic units present in the estuary, magnetic data were processed by multivariate statistical analyses. Our numerical simulation show a large inundation of the estuary with flow depths varying from 0.5 to 6 m and run up of ～7 m. Magnetic data show a dominance of paramagnetic minerals (quartz) mixed with lesser amount of ferromagnetic minerals, namely titanomagnetite and titanohematite both of a detrital origin and reworked from the underlying units. Multivariate statistical analyses indicate a better connection between the tsunami-induced deposit and a mixture of Units C and D. All these results point to a scenario where the energy released by the tsunami wave was strong enough to overtop and erode important amount of sand from the littoral dune and mixed it with reworked materials from underlying layers at least 1 m in depth. The method tested here represents an original and promising tool to identify tsunami-induced deposits in similar embayed beach environments.     

Functional Performance of Three Invasive <Emphasis Type="Italic">Marenzelleria</Emphasis> Species Under Contrasting Ecological Conditions Within the Baltic Sea

A 4-week laboratory experiment investigated the behaviour (survival and bioirrigation) and impact of the invasive polychaetes Marenzelleria viridis, M. neglecta and M. arctia on sediment-water solutes exchange, porewater chemistry, and Fe and P interactions in high-salinity sandy sediment (HSS) and low-salinity muddy sediment (LSM) from the Baltic Sea. M. viridis showed deep burrowing with efficient bioirrigation (11 L m^?2 day^?1) and high survival (71%) in HSS, while M. arctia exhibited shallow burrowing with high bioirrigation (12 L m^?2 day^?1) and survival (88%) in LSM. M. neglecta behaved poorly in both ecological settings (bioirrigation, 5–6 L m^?2 day^?1; survival, 21–44%). The deep M. viridis bioirrigation enhanced total microbial CO₂ (TCO₂) production in HSS by 175% with a net efflux of NH₄⁺ and PO₄^3?, at rates 3- to 27-fold higher than for the other species. Although the shallow and intense bioirrigation of M. arctia in LSM stimulated microbial TCO₂ production to some extent (61% enhancement), the nutrient fluxes close to zero indicate that it effectively prevented the P release. Porewater Fe:PO₄^3? ratios revealed that the oxidizing effect of M. arctia bioirrigation increased the PO₄^3? adsorption capacity of LSM twofold relative to defaunated controls while no buffering of PO₄^3? was detected in M. viridis HSS treatment. Therefore, the different behaviour of the three species in various environments and the sharp contrast between M. viridis and M. arctia effects on C, N and P cycling must be considered carefully when the ecological role of Marenzelleria species in the Baltic Sea is evaluated.     

A double structure generalized plasticity model for expansive materials

The constitutive model presented in this work is built on a conceptual approach for unsaturated expansive soils in which the fundamental characteristic is the explicit consideration of two pore levels. The distinction between the macro‐ and microstructure provides the opportunity to take into account the dominant phenomena that affect the behaviour of each structural level and the main interactions between them. The microstructure is associated with the active clay minerals, while the macrostructure accounts for the larger‐scale structure of the material. The model has been formulated considering concepts of classical and generalized plasticity theories. The generalized stress–strain rate equations are derived within a framework of multidissipative materials, which provides a consistent and formal approach when there are several sources of energy dissipation. The model is formulated in the space of stresses, suction and temperature; and has been implemented in a finite element code. The approach has been applied to explaining and reproducing the behaviour of expansive soils in a variety of problems for which experimental data are available. Three application cases are presented in this paper. Of particular interest is the modelling of an accidental overheating, that took place in a large‐scale heating test. This test allows the capabilities of the model to be checked when a complex thermo‐hydro‐mechanical (THM) path is followed. Copyright © 2005 John Wiley & Sons, Ltd.     

Estimation of the seismic wavelet through homomorphic deconvolution and well log data: application on well-to-seismic tie procedure

Wavelet estimation and well-tie procedures are important tasks in seismic processing and interpretation. Deconvolutional statistical methods to estimate the proper wavelet, in general, are based on the assumptions of the classical convolutional model, which implies a random process reflectivity and a minimum-phase wavelet. The homomorphic deconvolution, however, does not take these premises into account. In this work, we propose an approach to estimate the seismic wavelet using the advantages of the homomorphic deconvolution and the deterministic estimation of the wavelet, which uses both seismic and well log data. The feasibility of this approach is verified on well-to-seismic tie from a real data set from Viking Graben Field, North Sea, Norway. The results show that the wavelet estimated through this methodology produced a higher quality well tie when compared to methods of estimation of the wavelet that consider the classical assumptions of the convolutional model.     

On the determination of marine magnetotelluric receiver orientation using land magnetic observatory data

Marine magnetotelluric measurements using “free‐fall’’ instruments without effective compasses suffer from the problem of unknown orientation of the receivers at the seafloor. While past works indicate that marine magnetotelluric orientation of the instruments can be estimated by reference to land deployments of known orientation using the transfer tensor method, there is limited published information on how this is implemented in practice. We document this method and propose a set of new time‐ and frequency‐domain approaches to solve this orientation problem of the seafloor receivers. We test these methodologies in onshore and offshore magnetotelluric data whose orientations are well known and apply these techniques to marine magnetotelluric data with unknown orientation. For the controlled tests, both time‐ and frequency‐domain approaches produce overall comparable results. To investigate the effects of the subsurface structure distribution on the orientation process, a dimensionality analysis of a controlled dataset is carried out. In subsequent analysis using the available disoriented marine magnetotelluric data from offshore Brazil and from the Vassouras magnetic observatory on the mainland for remote referencing, frequency‐domain methods yield approximate orientation angles among themselves with low standard deviation each. Time‐domain results are consistent for most cases but differ from frequency‐domain results for some situations.     

What feeds shelf-edge clinoforms over margins deprived of adjacent land sources? An example from southeastern Brazil

In southeastern Brazil, the Serra do Mar coastal mountain range blocks the sediment influx from arriving at a ca. 1,500 km long continental margin comprising Santos and Pelotas basins. Despite this deprivation, the margin accumulated a ca. 1 km thick sedimentary succession since the Mid-Miocene. Examination of seismic reflection and oceanographic data indicates that shelf-margin clinoform formation exhibits a regional variability, with major sigmoidal clinoforms developed in the transitional area between both basins. Laterally, poorly developed oblique clinoforms constitute isolated depocenters along the shelf margin. The continuous clinoform development in the transitional area is attributed to the major influence on sediment transport patterns of several ocean bottom currents flowing along the margin, such as the Brazil Coastal Current, the Brazil Current and the Intermediate Water Brazil Current. These currents erode, transport and distribute sediments across the shelf break and upper slope from distant sediment sources located either north or south of the study area. The progressive southward strengthening of the Brazil Current could be responsible for a major southward sediment redistribution from the northern Campos Basin, and/or for sediment entrainment from northward-induced transport by the Brazil Coastal Current, originally derived from the De la Plata Estuary. In the transition between Santos and Pelotas basins, the Intermediate Water Brazil Current splits forming the Santos Bifurcation, allowing for a continuous depositional process and clinoform generation. We suggest that ocean bottom currents may shape other shelf-edge ‘contouritic clinoforms’ in continental margins mainly constructed by along-strike sediment transport largely driven by long-term geostrophic currents.     

The solar, exoplanet and cosmological lithium problems

We review three Li problems. First, the Li problem in the Sun, for which some previous studies have argued that it may be Li-poor compared to other Suns. Second, we discuss the Li problem in planet hosting stars, which are claimed to be Li-poor when compared to field stars. Third, we discuss the cosmological Li problem, i.e. the discrepancy between the Li abundance in metal-poor stars (Spite plateau stars) and the predictions from standard Big Bang Nucleosynthesis. In all three cases we find that the “problems” are naturally explained by non-standard mixing in stars.     

Estimating quality factor from surface seismic data: A comparison of current approaches

The performances of the spectral ratio (SR), frequency centroid shift (FCS), and frequency peak shift (FPS) methods to estimate the effective quality factor Q are compared. These methods do not demand true amplitude data and their implementations were done following an “as simple as possible” approach to highlight their intrinsic potentials and limitations. We use synthetic zero-offset seismic data generated with a simple layer-cake isotropic model. The methods can be ranked from simple to complex in terms of automation as: FPS, FCS and SR. This is a consequence of: (i) peak identification consists basically of a sorting procedure, (ii) centroid estimation involves basically the evaluation of two well-behaved integrals, and (iii) implementation of the SR method involves at least choosing a usable frequency bandwidth and fitting a gradient. The methods can be ranked from robust to sensitive in the presence of noise content in the sequence SR, FCS, and FPS. This is consequence of: (i) the gradient estimate associated to the SR method averages out the noise content in the entire usable frequency bandwidth, (ii) in the presence of moderate-to-high noise level, the centroid estimation is biassed towards overestimating Q due to noise contribution in the tail of the amplitude spectrum, and (iii) peak identification is unstable due to local noise fluctuation in the amplitude spectrum around the peak frequency. Regarding the stability of the estimates relative to the attenuation amount, SR and FCS methods show similar behaviours, whereas FPS method presents an inferior performance. This fact is an indirect consequence of the sensitivity of FPS method to the noise content because the higher is the attenuation the lower is the signal-to-noise ratio. Finally, regarding the robustness of the methods to the presence of dipping layers, only SR and FCS methods provide good estimates, at least to typical dips in non-faulted sedimentary layers, with the estimates obtained with SR method being more accurate that those obtained with FCS method. Except in relation to the automation complexity, which is less important than the performances of the methods, SR method was superior or showed similar performance to FCS method in all scenarios we tried.