Occurrence of roll circulations in a shallow boundary layer     

Ann -Sofi Smedman 《Boundary-Layer Meteorology》1991,57(4):343-358

Meteorological measurements taken at the Näsudden wind turbine site during slightly unstable conditions have been analyzed. The height of the convective boundary layer (CBL) was rather low, varying between 60 and 300 m. Turbulence statistics near the ground followed Monin-Obukhov similarity, whereas the remaining part of the boundary layer can be regarded as a near neutral upper layer. In 55% of the runs, horizontal roll vortices were found. Those were the most unstable runs, with -z _i/L > 5. Spectra and co-spectra are used to identify the structures. Three roll indicators were identified: (i) a low frequency peak in the spectrum of the lateral component at low level; (ii) a corresponding increase in the vertical component at mid-CBL; (iii) a positive covariance {ovvw} together with positive wind shear in the lateral direction (V/z) in the CBL. By applying these indicators, it is possible to show that horizontal roll circulations are likely to be a common phenomenon over the Baltic during late summer and early winter.  相似文献   

Kinetic rate laws derived from order parameter theory IV: Kinetics of Al,Si disordering in Na-feldspars     

Bernd Wruck  Ekhard K. H. Salje  Ann Graeme-Barber 《Physics and Chemistry of Minerals》1991,17(8):700-710

The kinetic rate laws of Al-Si disordering under dry conditions (T = 1353K, 1253 K, 1223 K, 1183 K) and in the presence of water (p = 1 kbar, T = 1023 K, 1073 K, 1103 K) were studied both experimentally and theoretically. A gradual change of the degree of order was found under dry conditions. For intermediate degrees of order broad distributions of the order parameter Q _od occur. The variations of Q _od are correlated with structural modulations as observed in the transmission electron microscope. The time evolution of the mean value of Q _od can be well described by the rate law: $$\frac{{dQ_{od} }}{{dt}} = - \frac{\gamma }{{RT}}\exp \sum\limits_{i = 1}^n {X_i^2 } \left[ {\frac{{ - (G_a^0 + \varepsilon (\Delta Q_{od} )^2 )}}{{RT}}} \right]\frac{{dG}}{{dQ_{od} }}$$ with the excess Gibbs energy G and G _a ⁰ = 433.8 kJ/mol, ?= -27.4 kJ/mol, γ = 1.687 · 10¹⁴ h ^?1. Under wet conditions, two processes were found which occur simultaneously. Firstly, some material renucleated with the equilibrium degree of order. Secondly, the bulk of the material transformed following the same rate law as under dry conditions but with the reduced activation energy G _a ⁰ = 332.0 kJ/mol and ? = -43.0 kJ/ mol, γ = 1.047 · 10¹³ h^?1. The applicability of the kinetic theory is discussed and some ideas for the analysis of geological observations are evolved.  相似文献   

Tracking hydrological responses of a thermokarst lake in the Old Crow Flats (Yukon Territory,Canada) to recent climate variability using aerial photographs and paleolimnological methods     

Lauren A. MacDonald  Kevin W. Turner  Ann M. Balasubramaniam  Brent B. Wolfe  Roland I. Hall  Jon N. Sweetman 《水文研究》2012,26(1):117-129

Recent studies using remote sensing analysis of lake‐rich thermokarst landscapes have documented evidence of declining lake surface area in response to recent warming. However, images alone cannot identify whether these declines are due to increasing frequency of lake drainage events associated with accelerated thermokarst activity or to increasing evaporation in response to longer ice‐free season duration. Here, we explore the potential of combining aerial photograph time series with paleolimnological analyses to track changes in hydrological conditions of a thermokarst lake in the Old Crow Flats (OCF), Canada, and to identify their causes. Images show that the water level in lake OCF 48 declined markedly sometime between 1972 and 2001. In a sediment core from OCF 48, complacent stratigraphic profiles of several physical, geochemical, and biological parameters from ～1874–1967 indicate hydro‐limnological conditions were relatively stable. From ～1967–1989, declines in organic matter content, organic carbon isotope values, and pigment concentrations are interpreted to reflect an increase in supply of minerogenic sediment, and subsequent decline in aquatic productivity, caused by increased thermo‐erosion of shoreline soils. Lake expansion was likely caused by increased summer rainfall, as recorded by increased cellulose‐inferred lake‐water oxygen isotope compositions. Stratigraphic trends defining the lake expansion phase terminated at ～1989, which likely marks the year when the lake drained. Above‐average precipitation during the previous year probably raised the lake level and promoted further thermo‐erosion of the shoreline soils that caused the lake to drain. These are meteorological conditions that have led to other recent lake‐drainage events in the OCF. Thus, the decline in lake level, evident in the aerial photograph from 2001, is unlikely to have been caused by evaporation, but rather is a remnant of a drainage event that took place more than a decade earlier. After drainage, the lake began to refill, and most paleolimnological parameters approach levels that are similar to those during the stable phase. These findings indicate that combined use of aerial images and paleolimnological methods offers much promise for identifying the hydrological consequences of recent climatic variations on thermokarst lakes. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Coastal uplift rate at Matanzas (Cuba) inferred from MIS5e phreatic overgrowths on speleothems          下载免费PDF全文

Jo De Waele  Ilenia M. D'Angeli  Nicola Tisato  Paola Tuccimei  Michele Soligo  Joaquín Ginés  Angel Ginés  Joan J. Fornós  Igor M. Villa  Esteban R. Grau González  Stefano M. Bernasconi  Tomaso R. R. Bontognali 《地学学报》2017,29(2):98-105

Many morphological elements in Cuba's landscape (e.g. marine terraces, tidal notches) demonstrate that coastal uplift has taken place, but the rate at which this occurs is not known. Carbonate phreatic overgrowths on speleothems have been found in a cave in Central North Cuba, ~1 km from the present coastline at 16 m asl. They form exceptional and unique mushroom‐shaped speleothems and balconies decorating the walls of the rooms. These phreatic overgrowths on speleothems (POS) formed at the oscillating air–water interface in sea‐level controlled anchialine lakes. U/Th dating of these overgrowths suggests ages that are compatible with the Marine Isotope Stage 5e (i.e. 130–115 ka). These POS have fixed this sea‐level highstand and demonstrate that this part of Cuba has been subjected to a much lower uplift rate than previously reported, that is, less than 0.1 mm/year since the last interglacial.  相似文献   

A Last Glacial Maximum pollen record from Bodmin Moor showing a possible cryptic northern refugium in southwest England     

Ann Kelly  Dan J. Charman  Rewi M. Newnham 《第四纪科学杂志》2010,25(3):296-308

A late Devensian palynological record is presented from Dozmary Pool (Bodmin Moor, southwest England), beyond the southern limit of the Last Glacial Maximum (LGM) British Ice Sheet. The pollen assemblages indicate predominantly herbaceous tundra–steppe communities but also include elevated levels (typically 10–20%) of conifer tree pollen (Picea, Pinus, Abies) and lower but persistent percentages of broadleaf tree pollen during the LGM. This record is seemingly at odds with the orthodox view of an entirely treeless tundra–steppe environment for this region and elimination of tree species from the British Isles during glacial maxima. Long‐distance pollen transport seems an unlikely explanation for the tree pollen considering distance to the nearest known refugia, except possibly for Pinus. Reworking of the tree pollen, often invoked in these circumstances, remains a possible alternative, especially given the abundance of these trees in the region during early Devensian interstadials. However, this explanation has been challenged by studies reporting plant macrofossil and faunal evidence for survival of temperate biota during glacial maxima and from climate modelling work that suggests some trees could have survived the glacial extremes in areas well beyond the recorded glacial refugia. Assuming reworking was not a major factor, the Dozmary Pool pollen record is consistent with the ‘cryptic northern refugia hypothesis’ that invokes survival of trees in small, scattered populations under locally favourable conditions during glacial maxima. Copyright © 2009 John Wiley & Sons, Ltd.  相似文献   

Nematode diversity and its relation to the quantity and quality of sedimentary organic matter in the deep Nazaré Canyon,Western Iberian Margin     

Jeroen Ingels  Konstadinos Kiriakoulakis  George A. Wolff  Ann Vanreusel 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(9):1521-1539

Samples collected in the deep Nazaré Canyon and at the adjacent slope, during the HERMES RRS Discovery D297 cruise (2005), were analysed for metazoan meiofauna, nematode structure and diversity and its relation to quality and quantity of sedimentary organic material. The amount and quality of organic matter available for direct consumption was much higher in the canyon compared to the slope and positively correlated with high nematode abundances (795–1171 ind. 10 cm^?2) and biomass (93.2–343.5 μg dry weight 10 cm^?2), thus leading to higher standing stocks. Canyon nematode assemblages also showed particular adaptations (e.g. higher trophic complexity, variability of nematode morphology, and presence of opportunistic genera) to canyon conditions, particularly in the deeper sediment layers. The Nazaré Canyon's nematode diversity was slightly lower than that of the adjacent slope and its assemblages were characterised by a higher dominance of certain genera. Still, the canyon contributes considerably to total Western Iberian Margin diversity due to different assemblages present compared to the slope. Furthermore, the harsh conditions in terms of hydrodynamic disturbance and the high organic matter flux are likely to have a negative impact on the establishment of species rich meiobenthic communities, especially in the canyon axis.  相似文献   

Near-infrared imaging of 222 nearby Hδ-strong galaxies from the Sloan Digital Sky Survey     

Michael L. Balogh  Chris Miller  Robert Nichol  Ann Zabludoff  Tomo Goto 《Monthly notices of the Royal Astronomical Society》2005,360(2):587-609

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Is being in work good for wellbeing? Work Integration Social Enterprises in regional Australia     

Katharine McKinnon  Melissa Kennedy  Jo Barraket  Tracy DeCotta 《The Australian geographer》2020,51(3):361-375

ABSTRACT

Work Integration Social Enterprises (WISE) offer supported work environments for people experiencing disadvantage, including people with disability. This paper reflects on a research project that is mapping the ways in which social enterprises in regional Australian cities produce wellbeing for their employees. Through supported employment programs, these organisations are transforming individual lives, helping to build a sense of self-worth and purpose, and increase individuals’ social skills and capacities. Many of the perceived benefits are associated with a belief in the innate good of paid work. Based upon interviews with employees in the social enterprises, it is apparent that the hopes attached to providing ‘meaningful work’ are considerable. At the same time social enterprises are taking on social responsibilities that were once provided by the state, while also selling their services as employers of disabled and disadvantaged members of society and maintaining commercial viability of the enterprise. Using feminist political economy alongside discussion of the distributive economy, this paper explores how contemporary policy conditions, productivist biases and normative discourses about the value of wage work inflect the forms of wellbeing that can be experienced by WISE workers.  相似文献   

The Local Ensemble Transform Kalman Filter (LETKF) with a Global NWP Model on the Cubed Sphere     

Seoleun Shin  Ji-Sun Kang  Youngsoon Jo 《Pure and Applied Geophysics》2016,173(7):2555-2570

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Controls on regional variability in marine pore-water diagenesis below the seafloor in Upper Jurassic–Lower Cretaceous prodeltaic sandstone and shales,Scotian Basin,Eastern Canada     

Ann C. Okwese  Georgia Pe-Piper  David J.W. Piper 《Marine and Petroleum Geology》2012,29(1):175-191

Diagenesis in the uppermost Jurassic to Lower Cretaceous deltaic sandstones and shales of the Scotian Basin is an important control on reservoir quality. Ferruginous zone (sub-oxic) marine pore-water diagenesis controls the initial formation of Fe²⁺-silicates that are the precursors of grain-rimming chlorite that preserves porosity. This study assesses the regional controls on the type of marine pore-water diagenesis by studying the sedimentology, mineralogy, and geochemistry of the retrogradational units and underlying progradational units in parasequences from conventional cores in two wells in different parts of the basin. Coated grains preserve a record of whether marine pore-water diagenesis below the seafloor was dominantly in the ferruginous or sulphidic geochemical zone. Four types of coated grain were distinguished, each with a different mineral paragenesis. Mineralogical and chemical evidence of ferruginous zone diagenesis includes the presence of diagenetic chlorite and siderite, and the correlation of P with Fe or Ti. Pyrite and Fe-calcite are found where the sulphidic zone is more significant than the ferruginous zone. Ferruginous zone diagenesis was common in low-sedimentation rate retrogradational sediments with low organic carbon, and in delta-front turbidites and river-mouth sandstones. Estuarine, tidal flat and prodeltaic facies that are directly supplied by riverine sediments have a lower Fe:Ti ratio than do fully marine shoreface and open shelf facies as a result of input of detrital ilmenite and its alteration products. The relative contribution of colloidal iron (hydr)-oxides appears greater in distal low-sedimentation rate environments. Where large changes in sedimentation rate occurred at ravinement surfaces, the underlying progradational rocks have evidence of ferruginous zone diagenesis, whatever their facies. Rapid upward migration of the pore-water profile resulting from the change in sedimentation rate reduced the time available for mineral products to form in the deeper pore-water zones. This study has shown that the availability of Fe and organic carbon varying in a complex manner in marine deltaic sediments, but that the resulting diagenesis by marine pore-water can be predicted from facies and paleogeographic setting.  相似文献