On the bogussing of tropical cyclones in numerical models: A comparison of vortex profiles

Summary At the resolutions currently in use, and with the sparse oceanic data coverage, numerical analyses cannot adequately represent tropical cyclone circulations for use in numerical weather prediction models. In many cases there is no circulation present at all. Most numerical weather prediction centers therefore employ a bogussing scheme to force a tropical cyclone vortex into the numerical analysis. The standard procedure is to define a synthetic data distribution based on an analytically prescribed vortex, which is passed to the analysis scheme as a set of high quality observations.In this study, four commonly used bogus vortices are examined by comparing resultant forecast tracks in an environment at rest, and in a background flow that simulates a typical monsoon trough-subtropical ridge structure. There are three main findings, each of which has significance for operational tropical cyclone track prediction. First, great care is needed in the choice of the characteristics of the bogus vortex, such as the radius and magnitude of the maximum wind. Second, the tropical cyclone trajectories can be very sensitive to their initial position in the idealised environment. Third, the bogus vortex can substantially influence the environment, especially over longer time periods and for vortices of larger size.With 9 Figures     

Daily rainfall domains in Mallorca

Summary A Pearson Product Moment Correlation matrix for four years of daily rainfall from 96 sites on the island of Mallorca has been used to derive and map correlation fields and construct composite correlation fields for different parts of the island based on previously defined daily rainfall affinity areas. Significant variations in rainfall organisation over the island are revealed. These reflect the dominance of uplift and exposure by upland areas in the generation of rainfall, evidenced in strongly anisotropic correlation fields. Further anisotropy along lowland coasts normal to the relief trend indicate the role of local rainfall generation along sea-breeze fronts. Near isotropic fields for central island locations highlight the importance of local convection and local convergence between opposing sea breeze systems and inland convection. Linear correlation distance-decay trends are determined for the island and for the predetermined rainfall affinity areas, including estimates of distance-decay rates along field axes. A suite of exponential cone functions is derived to model the empirically observed fields, representing their typical bidimensional structure. Use of the fitted cones to model a typical rainfall day, where the rainfall distribution mimics quite closely the longer term average, yields quite good results and suggests that their use may be more appropriate than applying more conventional general interpolation techniques in the mapping of spatial rainfall distributions.With 14 Figures     

Geology of the volcanic-hosted Brockman rare-metals deposit,Halls Creek Mobile Zone,northwest Australia. l. Volcanic environment,geochronology and petrography of the Brockman volcanics

Summary Rare-metals mineralization of the Brockman deposit (Halls Creek Mobile Zone, NW Australia) is hosted in a fluorite-bearing, rhyolitic volcaniclastic unit informally termed the Niobium Tuff. The Tuff, more correctly described as a tuffaceous volcaniclastic deposit, is the lowermost unit of a sequence of trachyte-to-rhyolite lavas, trachyandesite subvolcanic rocks, and volcaniclastic units of the Brockman volcanics located within the Halls Creek Group, a thick, early Proterozoic volcano-sedimentary sequence. High precision SHRIMP ion-microprobe zircon dating of the Niobium Tuff gives an eruption age of 1870 ± 4 Ma. Regional geochronological constraints indicate the Niobium Tuff was deposited about 15 Ma before major orogenic activity affected the area. Despite folding, faulting and low-grade metamorphism, the Brockman volcanics show excellent preservation of primary volcanological features, including pillow-lavas and pillow-breccias, that suggest a dominantly subaqueous, below-wave-base emplacement environment. The style of eruption products and magma volume constraints suggest the trachyte-dominated volcanics were erupted from a small shield volcanic complex probably in a rift-related basin in a shallow-marine setting. The tectonic setting was intraplate but differs from most Tertiary to recent trachyte volcanic complexes which are largely subaerial, are built on relatively thick continental crust, and show no post-eruptive orogenic history. Brockman-style rare-metal deposits are characterized by preservation of subaqueous volcanics beneath a thick sedimentary sequence, eruption of early incompatible-element enriched products followed by less differentiated magmas, and fine-grained mineralogy influenced by alteration processes. Prospects exist for discovery of analogous deposits, particularly in early Proterozoic mobile belts and Tertiary intraplate shield volcanic provinces.

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Geologie der an Vulkanite gebundenen Seltene-Metalle-Lagerstätte Brockman, Halls Creek Mobile Zone, Nordwest-Australien. I. Vulkanologie, Geochronologie und Petrographie der Brockman-Vulkanite

Zusammenfassung Selten-Metall-Vererzung der Brockman-Lagerstätten (Halls Creek Mobile Zone, NW Australien) sitzt in einer Fluorit-führenden, rhyolitischen vulkanoklastischen Einheit auf, die informell als der Niob-Tuff bezeichnet wird. Es handelt sich hier um ein vulkanoklastisches Tuff-Sediment; dieses ist die unterste Einheit einer Abfolge vor Trachyt bis Rhyolit-Laven, trachyandesitischen Subvulkaniten and vulkanoklastischen Einheiten der Brockman Vulkanite innerhalb der Halls Creek Gruppe, einer mächtigen frühproterozoischen vulkanosedimentdren Abfolge. Prüzisionsdatierungen des Niob Tuffs mit der SHRIMP Ionen-Mikrosonde ergeben ein Eruptionsalter von 1870 +-4 Millionen Jahren. Regionale geochronologische Zusammenhänge zeigen, daß der Niob Tuff etwa 15 Millionen Jahre vor einer größeren Orogenese, die das Gebiet betroffen hat, abgelagert wurde. Trotz Faltung, Bruchtektonik and niedriggradiger Metamorphose zeigen die Brockman-Vulkanite einen hervorragenden Erhaltungszustand primärer vulkanologischer Erscheinungen. Diese urnfassen auch Kissenlaven und KissenBreckzien, die eine vorwiegend subaquatische Ablagerung in ruhigem Wasser erkennen lassen. Die Art der Eruptionsprodukte and das Magmavolumen zeigen, daß die Trachytdominierten Vulkanite von einem kleinen Schildvulkan stammer, wahrscheinlich in einem Becken in einer Rift-Situation im seichten marinen Milieu. Die tektonische Situation war intraplate, aber unterscheidet sich von den meisten tertiären bis rezenten trachytischen Vulkan-Komplexen, die hauptsächlich subaerisch sind, auf einer relativ mächtigen kontinentalen Kruste aufsitzen, and keine post-eruptive orogene Entwicklung zeigen. Seltene-Metalle-Lagerstatten des Brockman-Typs rind durch die Erhaltung subaquatischer-Vulkanite unterhalb einer machtigen sedimentdren Abfolge gekennzeichnet; welters durch frühe Eruptionsprodukte, die an inkompatiblen Elementen angereichert sind, auf die dann weniger differenzierte Magmen folgten, und schließlich durch einen feinkörnigen Mineralbestand, der vor Umwandlungsprozessen betroffen war. Es besteht die Möglichkeit der Entdeckung analoger Lagerstätten, besonders in frühproterozoischen mobilen Gürteln und in tertidren intraplate Schildvulkan Provinzen.

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Deceased     

Efficient generation of conditional simulations by chebyshev matrix polynomial approximations to the symmetric square root of the covariance matrix

Consider the problem of generating a realization y₁ of a Gaussian random field on a dense grid of points ₁ conditioned on field observations y₂ collected on a sparse grid of points ₂. An approach to this is to generate first an unconditional realization y over the grid =_{1 2}, and then to produce y₁ by conditioning y on the data y₂. As standard methods for generating y, such as the turning bands, spectral or Cholesky approaches can have various limitations, it has been proposed by M. W. Davis to generate realizations from a matrix polynomial approximations to the square root of the covariance matrix. In this paper we describe how to generate a direct approximation to the conditional realization y₁, on ₁ using a variant of Davis' approach based on approximation by Chebyshev polynomials. The resulting algorithm is simple to implement, numerically stable, and bounds on the approximation error are readily available. Furthermore we show that the conditional realization y₁ can be generated directly with a lower order polynomial than the unconditional realization y, and that further reductions can be achieved by exploiting a nugget effect if one is present. A pseudocode version of the algorithm is provided that can be implemented using the fast Fourier transform if the field is stationary and the grid ₁ is rectangular. Finally, numerical illustrations are given of the algorithm's performance in generating various 2-D realizations of conditional processes on large sampling grids.     

Trace elements distribution and mineralogical composition in the < 2-μm size fraction of shales from the Southern Apennines,Italy

Summary Mineralogical composition and trace elements distribution in the < 2-m size fraction of Late Cretaceous-Oligocene shales from the Southern Apennines (Italy) are presented.The clay mineral assemblage consists of illite, smectite, kaolinite and minor chlorite. Analytical evidence points to a detrital micaceous precursor for illite and smectite. Accessory phases were also found. Chemical data, normalized with respect to the Post-Archean Australian Shales (PAAS), indicate depletion of Ba, Rb, Y, Zr and enrichment of Nb. PAAS-normalized REE-patterns exhibit a positive Eu anomaly and HREE depletion. A kaolinite-rich sample has high REE contents in contrast to smectite-rich fractions. A REE-pattern without appreciable Eu anomaly is displayed by the illite-rich sample.Statistical data processing indicates a link between Ti, P, Y, Zr, Nb and Yb, suggesting that accessory phases may play a role in controlling HREE and that the observed LREE/HREE fractionation may also be due to hydraulic sorting of these phases. An important La-kaolinite relationship accounts for the capability of this phase to host LREE. Smectite and, thus, adsorption mechanisms, appear to exert a limited role in distributing REE. The Eu anomaly is a source inherited feature, probably not determined solely by clay minerals.

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Spurenelement-Verteilung und mineralogische Zusammensetzung der < 2m Fraktion von Schiefern aus dem südlichen Appenin (Italien)

Zusammenfassung Die mineralogische Zusammensetzung und die Verteilung der Spurenelemente in der < 2 m Fraktion von spät-kretazischen-oligozänen Schiefern aus dem südlichen Appenin (Italien) werden in Übersicht gebracht. Die Tonmineral-Vergesellschaftung besteht aus Illit, Smectit, Kaolinit und kleineren Mengen von Chlorit. Analytische Daten weisen darauf hin, daß Illit und Smectit aus einem detritischen Glimmermineral hervorgegangen sein dürften. Auch akzessorische Phasen kommen vor. Chemische Daten zeigen gegenüber post-Archaischen australischen Schiefern (PAAS) eine Verarmung in Ba, Rb, Y, Zr und eine Anreicherung von Nb. PAAS-normalisierte SEE-Verteilungsmuster zeigen eine positive Eu Anomalie und eine Verarmung an HSEE. Eine Kaolinit-reiche Probe zeigt hohe Gehalte an gesamten SEE im Gegensatz zu einer Smectit-reichen. Die Illit-reiche Probe zeigt ein SEE-Verteilungsmuster ohne deutliche Eu Anomalie.Statistische Verarbeitung der Daten läßt eine Verbindung zwischen Ti, P, Y, Zr, Nb und Yb erkennen; dies weist darauf hin, daß akzessorische Phasen einen Einfluß auf die HSEE-Verteilung haben und daß die beobachtete LSEE/HSEE Fraktionierung auch auf hydraulische Sortierung dieser Phasen zurückgehen könnte. Es gibt eine bedeutsame Beziehung zwischen La und Kaolinit und diese unterstreicht die Fähigkeit des Kaolinits für die Aufnahme von LSEE. Smectit und Adsorptionsmechanismen scheinen eine geringe Rolle für die Verteilung der SEE zu spielen. Die Eu Anomalie ist eine Erscheinung, die auf die Quelle der sedimentären Minerale zurückgeht und wahrscheinlich nicht ausschließlich durch Tonminerale bestimmt wird.

     

Organic contaminants and characteristics of sediments from Oso Bay,south Texas,USA

The Oso Bay, Texas, sediments from nine sites were analyzed by GC-MS for organics to measure contamination in the bay. In most of the sites sediments contained tetrachloroethene (87–1433 g/kg), bis (2-ethylhexyl)phthalate (40–193 g/kg), and aliphatic hydrocarbons, C₈-C₁₃ (720–2491 g/kg). Sources of these contaminants include a landfill, military facilities, and municipal and industrial discharges. Size analysis of the sediments indicates they contain a high percentage of muddy sand (50–75 percent), which suggests that Oso Bay consists of common bay margin sediments.     

People and environment in the Russian far east from Paleolithic to Middle Ages: Chronology,palaeogeography, interaction

The Late Paleolithic sites existed in cold and dry climat (Ustinovka I, 10–25 ky ago; Ust-Ulma, 19, 360 ± 65 BP) with warmer stages (Suvorovo IV, 15,300 ± 140 BP) and on the Pleistocene/Holocene transition, near 10,000 BP (Suvorovo III). The Final Paleolithic sites existed in Late Glacial time, 10,000–12,000 BP (Gorbatka III, lower level) and in Boreal period, 8,000–9,000 BP (Ilistaya I, 7, 840 ± 60 BP; Timofeevka I). The Developed Neolithic sites existed during the warm and humid Middle-Late Atlantic period, 6,000–8,000 BP; the Late Neolithic sites — 3,000–5,000 BP. The human impact in the Paleolithic-Neolithic was restricted to burning and trampling the vegetation near the sites; the bases of paleoeconomy were hunting, fishing, gathering. The presence of pastoral anthropogenic indicators in pollen spectra of the Neolithic sites may reflect the beginning of cattle breeding.The Bronze Age (end of the 4th-2nd millenia BC) provides the first reliable evidence of cultivated plants (foxtail and Japanese millet) and domestic animals (pig, dog). In the paleoeconomy agriculture and cattle breeding appeared; the first stage of human impact increased (4,000–4,500 BP, ie 2550–3230 cal. BC) is reflected in pollen spectra from cultural layers. From the Early Iron Age to the Middle Ages (end of 2nd millenium BC-13th century AD) agriculture and cattle breeding were the base of paleoeconomy. From the 8th to the 10th centures AD, due to the development of ploughing (arable), the human impact intensified.Paper was presented on the 27th International Geographical Congress, Washington, DC, USA, August 9–14, 1992 (section Human Induced Environmental Change, the Ancient Past)     

Powder- and single crystal Mössbauer spectroscopy on synthetic fayalite

Mössbauer measurements on synthetic iron orthosilicate Fe₂SiO₄ (fayalite) were carried out in the antiferromagnetic spin state below T _N 65 K. The Mössbauer parameters isomer shift , inner magnetic field H(0), angle between H(0) and the z-component of the electric field gradient (efg), quadrupole splitting QS and asymmetry parameter were determined as a function of temperature. These parameters could be attributed to the two crystallographic sites M1 and M2.The smaller isomer shift on M1 with respect to M2 displays the more covalent character of the Fe-O bond on M1, which is supported by previous neutron diffraction experiments. H(0) shows a Brillouin-type behaviour with different fields on the two crystallographic sites (stronger on M1) and a small discontinuity at T = 23 K which corresponds with previous magnetic measurements. The quadrupole splitting is equal on both sites within error bars, in agreement with previous theoretical results and in contradiction to previous Mössbauer refinements published elsewhere.     

Mössbauer spectroscopic and x-ray powder diffraction studies of synthetic micas on the join annite KFe3AlSi3O10(OH)2-phlogopite KMg3AlSi3O10(OH)2

Micas of the composition K(Fe_3–x Mg _x )AlSi₃ O₁₀(OH)₂ (x=0.6, 1.2, 1.8, 2.4 and 3.0, corresponding to ann₈₀phl₂₀, ann₆₀phl₄₀, ann₄₀phl₆₀, ann₂₀phl₈₀ and ann₀phl₁₀₀) were synthesized hydrothermally under controlled oxygen fugacity conditions. Lattice parameters a ₀ and b ₀ show a distinct linear decrease with increasing Mg content. With increasing ferric iron content a deviation from this linear trend is observed especially within iron rich samples. The tetrahedral rotation angle increases smoothly from 0° in annite to 9.1° in phlogopite. Mössbauer spectra show Fe²⁺ and Fe³⁺ on the octahedral M1 and M2 sites and partially also Fe³⁺ on the tetrahedral site. There is a smooth increase of the quadrupole splitting on both the M1 and the M2 site going from annite to phlogopite, probably due to changes in the lattice contribution to the electric field gradient, assuming a positive correlation between quadrupole splitting and distortion. Fe³⁺ contents, as determined by Mössbauer spectroscopy, versus oxygen fugacity shows that, depending on the composition of the micas, minimum amounts of Fe³⁺ are present. For ann₈₀phl₂₀ this minimum amount of Fe³⁺ is about 8% decreasing to about 1–2% Fe³⁺ for ann₂₀phl₈₀.The molar volume of each solid solution member has been estimated from the determined relations of the molar volume versus % Fe³⁺ contents, extrapolated back to 0% Fe³⁺. Plotting these volumes as a function of X_phl shows that negative excess volume occur in the annitephlogopite join, with the maximum deviation from ideality around X _phl=0.3. Margules volume parameters have been constrained as: Wv, AnnPhl=0.018±0.016 J/(bar.mol) and Wv, PhlAnn=-0.391±0.025 J(bar.mol) (three site basis).     

Possible creep-related tilt precursors obtained in the Central Apennines (Italy) and in the Southern Caucasus (Georgia)

Daily averaged tilt component data from two sites of the Central Apennines (Italy) and of the Southern Caucasus (Georgia), respectively, revealed intermediate-term tilts as possible precursors to earthquakes (M=3.0÷4.7) which occurred in the above-mentioned seismic areas within a distance of 50 km from the sites. A good temporal correlation as well as a fair spatial correspondence between these residual tilts (with amplitude and duration of some microradians and months, respectively) and main shocks were pointed out, by removing both secular trends and seasonal thermoelastic effects from the raw tilts. An attempt was made to justify the above-mentioned results, based on the assumption that the observed intermediate-term preseismic tilts are the manifestation of aseismic creep episodes of comparable duration in the fault materials of thrust faults close to the tilt sites. The mechanism refers to a strain field slowly propagating from the preparation focal area to the tilt site, through crustal blocks separated by weak transition zones. This propagation is thought to be the cause of the local aseismic fault slip recorded by the tiltmeters. Previously, both discrete structures and strain propagation effects were revealed in the Central Apennines and are thought also to exist in the Southern Caucasus. As in the past, the rheological properties of fault materials are revealed as viscoelastic ones. In fact, creep equations obtained by applying several viscoelastic models on our data, proved to fit quite well some of the observed tilt precursors, producing viscosity and rigidity values very similar to those reported in literature.Professor Petr Viktorovich Manjgaladze died during the writing of this paper