Implementation of high-order particle-tracking schemes in a water column model     

Ulf Gräwe 《Ocean Modelling》2011,36(1-2):80-89

Stochastic differential equations (SDEs) offer an attractively simple solution to complex transport-controlled problems, and have a wide range of physical, chemical, and biological applications, which are dominated by stochastic processes, such as diffusion. As for deterministic ordinary differential equations (ODEs), various numerical scheme exist for solving SDEs. In this paper various particle-tracking schemes are presented and tested for accuracy and efficiency (time vs. accuracy). To test the schemes, the particle tracking algorithms are implemented into a community wide used 1D water column model. Modelling individual particles allows a straightforward physical interpretation of the involved processes. Further, this approach is strictly mass conserving and does not suffer from the numerical diffusion that plagues grid-based methods. Moreover, the Lagrangian framework allows to assign properties to the individual particles, that can vary spatially and temporally. The movement of the particles is described by a stochastic differential equation, which is consistent with the advection–diffusion equation. Here, the concentration profile is represented by a set of independent moving particles, which are advected according to the velocity field, while the diffusive displacements of the particles are sampled from a random distribution, which is related to the eddy diffusivity field.The paper will show that especially the 2nd order schemes are accurate and highly efficient. At the same level of accuracy, the 2nd order scheme can be significantly faster than the 1st order counterpart. This gain in efficiency can be spent on a higher resolution for more accurate solutions at a lower cost.  相似文献   

Provenance analysis of the Paleozoic sequences of the northern Gondwana margin in NW Iberia: Passive margin to Variscan collision and orocline development     

Daniel Pastor-Galán  Gabriel Gutiérrez-Alonso  J. Brendan Murphy  Javier Fernández-Suárez  Mandy Hofmann  Ulf Linnemann 《Gondwana Research》2013,23(3):1089-1103

The Cantabrian Zone of NW Iberia preserves a voluminous, almost continuous, sedimentary sequence that ranges from Neoproterozoic to Early Permian in age. Its tectonic setting is controversial and recent hypotheses include (i) passive margin deposition along the northern margin of Gondwana or (ii) an active continental margin or (iii) a drifting ribbon continent. In this paper we present detrital zircon U–Pb laser ablation age data from 13 samples taken in detrital rocks from the Cantabrian Zone sequence ranging from Early Silurian to Early Permian in depositional age. The obtained results, together with previously published detrital zircon ages from Ediacaran–Ordovician strata, allow a comprehensive analysis of changing provenance through time. Collectively, these data indicate that this portion of Iberia was part of the passive margin of Gondwana at least from Ordovician to Late Devonian times. Zircon populations in all samples show strong similarities with the Sahara Craton and with zircons found in Libya, suggesting that NW Iberia occupied a paleoposition close to those regions of present-day northern Africa during this time interval. Changes in provenance in the Late Devonian are attributed to the onset of the collision between Gondwana and Laurussia.Additionally, the Middle Carboniferous to Permian samples record populations consistent with the recycling of older sedimentary sequences and exhumation of the igneous rocks formed before and during the Variscan orogeny. Late-Devonian to Permian samples yield zircon populations that reflect topographic changes produced during the Variscan orogeny and development of the lithospheric scale oroclinal buckling.  相似文献   

Mixing,hypersalinity and gradients in Hervey Bay,Australia     

Ulf Gräwe  Jörg-Olaf Wolff  Joachim Ribbe 《Ocean Dynamics》2009,59(5):643-658

Hervey Bay, a large coastal embayment situated off the central eastern coast of Australia, is a shallow tidal area (average depth = 15 m), close to the continental shelf. It shows features of an inverse estuary, due to the high evaporation rate (approx. 2 m/year), low precipitation (less than 1 m/year) and on average almost no freshwater input from rivers that drain into the bay. The hydro- and thermodynamical structures of Hervey Bay and their variability are presented here for the first time, using a combination of four-dimensional modelling and observations from field studies. The numerical studies are performed with the Coupled Hydrodynamical Ecological Model for Regional Shelf Seas (COHERENS). Due to the high tidal range (>3.5 m), the bay is considered as a vertically well-mixed system, and therefore, only horizontal fronts are likely. Recent field measurements, but also the numerical simulations, indicate characteristic features of an inverse/hypersaline estuary with low salinity (35.5 psu) in the open ocean and peak values (>39.0 psu) in the head water of the bay. The model further predicts a nearly persistent mean salinity gradient of 0.5 psu across the bay (with higher salinities close to the shore). The investigation further shows that air temperature, wind direction and tidal regime are mainly responsible for the stability of the inverse circulation and the strength of the salinity gradient across the bay. Due to an ongoing drying trend, the occurrence of severe droughts at the central east coast of Australia and, therefore, a reduction in freshwater supply, the salinity flux out of the bay has increased, and the inverse circulation has also strengthened.  相似文献   

Estimating reaction norms for age and size at maturation with reconstructed immature size distributions: a new technique illustrated by application to Northeast Arctic cod   总被引：3，自引：1，他引：3  

Heino  Mikko; Dieckmann  Ulf; Godo  Olav Rune 《ICES Journal of Marine Science》2002,59(3):562-575

  相似文献   

Predation on herring, Clupea harengus, by minke whales, Balaenoptera acutorostrata, in the Barents Sea     

Lindstrom  Ulf; Haug  Tore; Rottingen  Ingolf 《ICES Journal of Marine Science》2002,59(1):58-70

  相似文献   

A precision kite or balloon-borne mini-sonde for wind and turbulence measurements     

Ann-Sofi Smedman  Knut Lundin  Hans Bergström  Ulf Högström 《Boundary-Layer Meteorology》1991,56(3):295-307

A highly mobile system for accurate measurements of wind speed and horizontal turbulence in the lowest few hundred meters of the atmosphere is presented. It consists of a light-weight sonde (only 50 g, including batteries that permit 12 h of continuous operation) which can be easily lifted by a small kite in winds below 5 m/s and up to at least 25 m/s. In winds below 5 m/s, a small kytoon may be used instead. The signals from the sonde are received by a standard FM-radio equipped with a frequency converter, and data are recorded on ordinary cassette tapes. Field tests against towermounted precision instruments were performed at two sites during neutral and unstable conditions with the sonde suspended 25 m below a small kite, the measuring heights being 11 and 18 m respectively during the two test series. Mean wind speeds are found to be accurate to within ±0.2 m/s. Wind speed spectra obtained with the flying sonde can be evaluated up to 0.5 Hz and are found to agree closely with the spectra of the longitudinal component recorded simultaneously by the tower-mounted instrument at the same height. After correction for high frequency loss, which amounted to 5% at this low height (it is expected to decrease rapidly with height), the standard deviation of the wind recorded by the sonde agreed to within 2% with that obtained by the reference instrument. A notable result of the field tests is that there was no sign of degradation of the performance of the sonde in strong turbulence conditions.  相似文献   

The MgCr2O4–MgFe2O4 solid solution series: effects of octahedrally coordinated Fe3+ on T–O bond lengths     

Davide Lenaz  Henrik Skogby  Francesco Princivalle  Ulf Hålenius 《Physics and Chemistry of Minerals》2006,33(7):465-474

The influence on the spinel structure of Fe³⁺ → Cr substitution was studied in flux-grown synthetic single crystals of the magnesiochromite–magnesioferrite (MgCr₂O₄–MgFe₂O₄) solid solution series. Samples were analysed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption and Mössbauer spectroscopy. With the exception of iron-poor samples (3–12 mol-% MgFe₂O₄), optical absorption and Mössbauer spectra show that iron occurs almost exclusively as trivalent Fe in the present samples. A very intense and broad absorption band at ca 7,800 cm^?1 dominates the optical absorption spectra of samples with higher Fe-contents. The appearance of this band is related to a distinct structural disorder of Fe³⁺ and a development of magnetic ordering as demonstrated by Mössbauer spectra. Profound composition-related changes are observed in the Mössbauer spectra, which are magnetically unsplit in the range 2–41 mol-% magnesioferrite, but become magnetically split in the range 59–100 mol-% magnesioferrite. Structural parameters a ₀ and M–O increase with magnesioferrite content and inversion degree, while u and T–O decrease. Our study confirms the previously reported (Lavina et al. 2002) influence of Fe³⁺ at the M site on T–O bond lengths in the spinel structure.  相似文献   

Long-term summer temperature variations in the Pyrenees   总被引：4，自引：0，他引：4  

Ulf Büntgen  David Frank  Håkan Grudd  Jan Esper 《Climate Dynamics》2008,31(6):615-631

Two hundred and sixty one newly measured tree-ring width and density series from living and dry-dead conifers from two timberline sites in the Spanish Pyrenees were compiled. Application of the regional curve standardization method for tree-ring detrending allowed the preservation of inter-annual to multi-centennial scale variability. The new density record correlates at 0.53 (0.68 in the higher frequency domain) with May–September maximum temperatures over the 1944–2005 period. Reconstructed warmth in the fourteenth to fifteenth and twentieth century is separated by a prolonged cooling from ∼1450 to 1850. Six of the ten warmest decades fall into the twentieth century, whereas the remaining four are reconstructed for the 1360–1440 interval. Comparison with novel density-based summer temperature reconstructions from the Swiss Alps and northern Sweden indicates decadal to longer-term similarity between the Pyrenees and Alps, but disagreement with northern Sweden. Spatial field correlations with instrumental data support the regional differentiation of the proxy records. While twentieth century warmth is evident in the Alps and Pyrenees, recent temperatures in Scandinavia are relatively cold in comparison to earlier warmth centered around medieval times, ∼1450, and the late eighteenth century. While coldest summers in the Alps and Pyrenees were in-phase with the Maunder and Dalton solar minima, lowest temperatures in Scandinavia occurred later at the onset of the twentieth century. However, fairly cold summers at the end of the fifteenth century, between ∼1600–1700, and ∼1820 were synchronized over Europe, and larger areas of the Northern Hemisphere.  相似文献   

Proterozoic mafic magmatism in Siberian craton: An overview and implications for paleocontinental reconstruction     

Dmitry P. Gladkochub  Sergei A. Pisarevsky  Tatiana V. Donskaya  Richard E. Ernst  Michael T.D. Wingate  Ulf Söderlund  Anatoliy M. Mazukabzov  Eugene V. Sklyarov  Michael A. Hamilton  John A. Hanes 《Precambrian Research》2010

We present a summary of late Paleoproterozoic to Neoproterozoic mafic magmatism in the Siberian craton, including recently published U–Pb and ⁴⁰Ar–³⁹Ar dates. These new precise ages suggest that at least some of the previously published K–Ar ages of Siberian mafic bodies should be ignored. The time–space geochronological chart, or the ‘barcode’ of mafic magmatic events shows significant differences between northern and southern Siberia. Both are characterized by ∼1900–1700 Ma magmatic events, but then there was an almost 1 Ga mafic magmatic ‘pause’ in south Siberia until ∼800 Ma. Meanwhile there are indications of multiple mafic magmatic events in North Siberia (Anabar shield and Olenek uplift) between ∼1600 and 1000 Ma. A series of magmatic events probably related to the breakup of Rodinia occurred in southern Siberia after ∼800 Ma. So far, there are no indications of late Neoproterozoic mafic magmatism in North Siberia. Ca. 1000–950 Ma mafic sills were reported from Meso- to Neo-Proterozoic sedimentary successions in the Sette-Daban area on the east side of the Siberian craton, but their tectonic setting is debated. Recent Ar–Ar dates of ∼1750 Ma for NW-trending dykes in the Aldan and Anabar shields, together with similar-age NNE-trending Baikal uplift dykes in south-eastern Siberia suggest the existence of a giant radial dyke swarm possibly related to a mantle plume centred in the Vilyui River area.  相似文献   

Coordination of boron in nominally boron-free rock forming silicates: Evidence for incorporation of BO₃ groups in clinopyroxene   总被引：1，自引：0，他引：1  

Ulf Hålenius  Henrik Skogby  Sabrina Nazzareni  Jeppa Resmark 《Geochimica et cosmochimica acta》2010,74(19):5672-1594

To explore mechanisms of B-incorporation in common chain silicates we have investigated synthetic diopside samples produced under boron-saturated conditions by ¹¹B and ²⁹Si magic-angle spinning (MAS) NMR and single-crystal NRA, FTIR, EMP and XRD/SREF techniques. Our samples contain 0.14-0.65 wt.% B₂O₃. NMR reveals that B is predominantly present in trigonal coordination in the clinopyroxene structure. This observation is supported by vibrational bands characteristic for B-O stretching in BO₃ groups in the range 1250-1400 cm⁻¹ in polarised single crystal FTIR-spectra. Single crystal structure refinements suggest that boron replaces Si at the T site. Combined, these results suggest that boron replacement for Si at the T-site leads to disruption of one of the T-O bonds of the nominal clinopyroxene structure resulting in replacement of SiO₄ tetrahedra by BO₃ groups. Our results show that high concentrations of boron can be incorporated in the nominally boron-free diopside. Elevated B-concentrations in the present calcic clinopyroxenes are accompanied by modifications of the diopside crystal structure involving the breaking of one T-O bond and simultaneous formation of vacancies at the octahedral M2 site. These structural modifications destabilize the structure and constitute thereby limiting factors for incorporating higher boron concentrations in diopside.  相似文献