A discrete spherical harmonics method for radiative transfer analysis in inhomogeneous polarized planar atmosphere

A discrete spherical harmonics method is developed for the radiative transfer problem in inhomogeneous polarized planar atmosphere illuminated at the top by a collimated sunlight while the bottom reflects the radiation. The method expands both the Stokes vector and the phase matrix in a finite series of generalized spherical functions and the resulting vector radiative transfer equation is expressed in a set of polar directions. Hence, the polarized characteristics of the radiance within the atmosphere at any polar direction and azimuthal angle can be determined without linearization and/or interpolations. The spatial dependent of the problem is solved using the spectral Chebyshev method. The emergent and transmitted radiative intensity and the degree of polarization are predicted for both Rayleigh and Mie scattering. The discrete spherical harmonics method predictions for optical thin atmosphere using 36 streams are found in good agreement with benchmark literature results. The maximum deviation between the proposed method and literature results and for polar directions \(\vert \mu \vert \geq0.1 \) is less than 0.5% and 0.9% for the Rayleigh and Mie scattering, respectively. These deviations for directions close to zero are about 3% and 10% for Rayleigh and Mie scattering, respectively.     

Mid‐Holocene environmental changes in the Bay of Skaill,Mainland Orkney,Scotland: an integrated geomorphological,sedimentological and stratigraphical study

A detailed multidisciplinary investigation of intertidal freshwater sediments exposed in the north of the Bay of Skaill, Mainland Orkney, Scotland, have revealed a complex sedimentary sequence. This provided evidence for dynamic coastal environmental changes in the area since the mid‐Holocene. Freshwater ponds developed on glacial sediments ca. 6550 ± 80 yr BP (cal. bc 5590–5305). From ca. 6120 ± 70 yr BP (cal. bc 5040–4855), these were infilled by blown sand from the distal edge of a dune ridge located to the west. Thereafter, a series of sand‐blow events alternating with periods of quiescence occurred until ca. 4410 ± 60 yr BP (cal. bc 3325–2900). Between ca. 5240 ± 160 and 4660 ± 80 yr BP (cal. bc 4370–3115), pollen and charcoal records show evidence of anthropogenic activities, associated with the nearby Neolithic settlement of Skara Brae. Agriculture was probably affected by recurrent sand movement and widespread deposition of calcium carbonate in the hinterland of the bay. Machair development between ca. 6100 and 5000 yr BP (cal. bc 5235–3540) corresponds to a mid‐Holocene phase of dune formation recorded elsewhere in northwest Europe. The more recent and progressive formation of the bay has probably been related to increasing external forcing via storminess, long‐term relative sea‐level change and sediment starvation within this exposed environment. Copyright © 2000 John Wiley & Sons, Ltd.     

Late Devensian ice sheet characteristics: a palaeohydraulic approach

Glacial meltwater channels are incised into bedrock and diamicton along much of the length of the Mid-Cheshire Ridge. Detailed mapping of one such system near the town of Helsby reveals a dendritic channel network developed in the opposite direction to the regional ice flow during the last (Late Devensian) glaciation. The channels formed subglacially, under atmospheric and not hydrostatic pressure, presumably as the ice sheet downwasted during deglaciation. Morphological and palaeohydraulic evidence suggests that not all of the network was necessarily active contemporaneously. Former water levels in the channels can be estimated due to the presence of bar surfaces, giving a calculated palaeodischarge of at least 111 m³ s⁻¹. The ablation rates required to account for this large discharge are an order of magnitude greater than those obtained from theoretical calculations and those observed in modern glacial environments. This implies that some form of high-magnitude discharge, such as a seasonal flood event, must have taken place in this area during deglaciation. This picture of the Late Devensian ice sheet suggests that during recession the ice sheet was static, crevassed and relatively thin (<50 m). This study also shows that there is no simple relationship between meltwater channel direction and ice dynamics, and that care is required when using the former to make inferences about the latter. Copyright © 1998 John Wiley & Sons, Ltd.     

Limit loads for an anchor/trapdoor embedded in an associative coulomb soil

A methodology for determining the plane strain limit load acting on an anchor or trapdoor buried within a purely associative Coulomb soil is presented. True lower bounds derived from a family of limiting stress fields appropriate to shallow horizontal trapdoors and anchors are shown to correlate to within less than 1 percent of upper bounds available in the literature, permitting the true limit load to be almost exactly defined. The solution form alters for deeply buried anchors and trapdoors resulting in poorer correlations. Methods by which the work may be extended to cover the more practical instances of non-associative Coulomb soils are indicated but are beyond the scope of the current paper. © 1998 John Wiley & Sons, Ltd.     

Hilbert–Huang transform analysis of storm waves

We use the Hilbert–Huang transform (HHT) for the spectral analysis of a North Sea storm that took place in 1997. We look at the contribution of the different Intrinsic Mode Functions (IMF) obtained using the Empirical Mode Decomposition algorithm, and also compare the Hilbert Marginal Spectra and the classical Fourier Spectra for the data set and the corresponding IMFs. We find that the number of IMFs needed to decompose the data and the energy associated to them is different from previous studies for different sea conditions by other authors. A tentative reason for this may lie in the difference in the sampling rate used.     

Benthic indicators and index approaches in the three main estuaries along the French Atlantic coast (Seine, Loire and Gironde)

The three main estuaries in the French Atlantic coast – the Seine, Loire and Gironde, all with high tidal regimes – are interfaces between the continental and the coastal ecosystems. The Seine and Gironde are highly contaminated, whereas the Loire remains in a more natural state. Both the Seine and Gironde have suffered from harbour construction, and as a result, their biological units are extremely compartmentalized. Benthic species and communities have adapted to tolerate temporal physical and chemical changes ( e.g. salinity, substrata, depth, and levels of fine particles and oxygen) and human activities ( e.g. dredging, shipping traffic, and habitat reduction). Although numerous bio-indicators and indices are used to define the ecological quality status (EcoQS) of coastal waters, very few of them were developed specifically for environments with a mosaic of conditions and salinity levels, including freshwater. The main problem appears to be that all the indices for determining anthropogenic stress examine the abundances of stress-tolerant species, which may also be able to tolerate natural stressors such as those occurring in estuaries. This paper takes a look at the development status of the benthic indicators and index approaches used in the three main estuaries along the French Atlantic coast. In addition, it examines the adaptation of the different benthic indicators to the taxonomic sufficiency principle, and the adaptation of the Benthic Opportunistic Polychaetes Amphipods index (BOPA) and the Benthic Opportunistic Annelida Amphipod index (BO2A) for use in the freshwater zones of transitional waters ( i.e. up to the upper limit of the tidal range). Several perspectives are discussed in light of the diverse disturbances and the heterogeneity of such stressed zones, such as the use of multimetric and scoring approaches.     

The effects of resolving the Canadian Arctic Archipelago in a finite element sea ice model

Though narrow straits may have a strong influence on the large-scale sea ice mass balance, they are often crudely represented in coarse resolution sea ice models. Unstructured meshes, with their natural ability to fit boundaries and locally increase the mesh resolution, propose an alternative framework to capture the complex oceanic areas formed by coasts and islands. In this paper, we develop a finite element sea ice model to investigate the sensitivity of the Arctic sea ice cover features to the resolution of the narrow straits constituting the Canadian Arctic Archipelago. The model is a two-level dynamic-thermodynamic sea ice model, including a viscous-plastic rheology. It is run over 1979–2005, forced by daily NCEP/NCAR reanalysis data. Confronting qualitatively numerical experiments with observations shows a good agreement with satellite and buoys measurements. Due to its simple representation of the oceanic interactions, the model overestimates the sea ice extent during winter in the southernmost parts of the Arctic, while the Baffin Bay and Kara Sea remain ice-covered during summer. In order to isolate the benefits from resolving the Canadian Arctic Archipelago, a numerical experiment is performed where we artificially close the archipelago. Focusing on the large-scale sea ice thickness pattern, no significant change is found in our model, except in the close surroundings of the archipelago. However, the local and short-term influences of the ice exchanges are nonnegligible. In particular, we show that the ice volume associated to the Canadian Arctic Archipelago represents 10% of the Northern Hemisphere sea ice volume and that the annual mean ice export towards Baffin Bay amounts to 125 km³ yr⁻¹, which may play an important role on the convective overturning in the Labrador Sea.     

The petrology and geochemistry of intrusive alkaline rocks of Elchuru,Prakasam District,Andhra Pradesh,India

The Elchuru alkaline igneous intrusion is an arcuate-shaped ring complex, approximately 16 km² in area, cropping out in the Eastern Ghats high grade metamorphic series. It is part of an alkaline province composed of a number of intrusions which range from ijolite-melteigite to alkali gabbro (viz. malignite, melalusitanite, shonkinite) and then to hypersolvus nepheline syenite followed by subsolvus nepheline syenite. The complex is cut by late lamprophyric dykes. A nephelinized alkaline gneiss, within the investigated complex, is the only deformed rock type and is regarded as an older unit not related to the comagmatic series. The remainder of the complex was emplaced post-tectonically. Sovitic carbonatite is a conspicuous Iithologic unit associated with the complex. Chemical analyses of 19 selected samples for 13 major oxides and 5 trace elements (Rb, Ba, Sr, Zr and Nb) are presented to establish a geochemical model for the investigated complex. The mineralogy, petrography and geochemistry of the rocks of the Elchuru Alkaline Complex suggest that it was formed by differentiation of an initially alkali-rich ijolitic magma as reflected in the crystallization of nepheline, kaersutitic amphibole and alkali feldspar. With progressive increase in alkali feldspar content (volume percentage) the ijolite passes to malignite and then nepheline syenites. Amphibole shows sodic enrichment from a dominant calcic variety. Pyroxene, likewise, shows sodic enrichment following the scheme salite-ferrosalite to aegirine-augite. The igneous cycle closes with the intrusion of biotite lamprophyre. There is a systematic increase in total alkalies (Na₂O+K₂O) and decrease in CaO from the early mafic rocks to the syenitic rocks. The alkali-lime index of the complex is 48 indicating its strongly alkaline nature (Peacock 1931), and they are miaskitic in character (agpaicity index <1, Currie 1976). Such miaskitic complexes are associated with carbonatites (Heinrich 1966).