The first and the second e of the extreme value distribution,EV1

In the peak over threshold model resulting in the Extreme-value distribution, type I, (EV1) the firste of the distribution function is based on the Poisson number of exceedances, and the seconde arises from the Exponentially distributed magnitudes.This paper, on the one hand, generalises the Poisson model to the (positive and negative) Binomial distribution, and, on the other hand, the Exponential distribution is generalised to the Generalised Pareto distribution. Lack of fit with respect to the Poisson and Exponential distribution is measured by statistics derived from those which would be locally most powerful if the estimates of the location and scale parameter were equal to the true parameter values. Ways of combining both statistics are discussed.     

Long-range weather forecasts through numerical and empirical methods

There has been much improvement in numerical weather prediction since L.F. Richardson (1922, Weather Prediction by Numerical Process, Cambridge University Press, Cambridge, p. 236) wrote his famous book. NWP has primarily been successful in improving day-by-day forecasts starting from an observed detailed Initial Condition (IC) out to about a week. The purpose of this paper is to discuss first the state of the art in long-range NWP by presenting results of a new large numerical experiment (named DERF90; from Dynamical Extended Range Forecasting in 1990 out to 90 days) conducted at the National Meteorological Center (NMC) during the summer and autumn of 1990 (Section 2). One hundred and twenty eight 90-day global forecasts were made from successive daily initial conditions (IC), thus giving us ample opportunity to assess skill of forecasts at lead times beyond 1 week.We then move on to define the notion of a limit of predictability (LOP), and following a procedure by Lorenz (1982), give a numerical estimate of the LOP using the DERF90 data set. We then produce a list of reasons, as to why this estimate (LOP = 18 days) should not be taken too literally. In particular, we argue that the LOP varies as a function of the flow itself, and it would be (much) larger if we had, as we will ultimately, a coupled ocean-atmosphere model for making long-lead forecasts. Last, but not least, we present results of empirical forecasts that point to modest but significant skill well beyond the traditional LOP (a few weeks).A specific recent example of empirical forecasting is discussed. Through Canonical Correlation Analysis (CCA), experimental forecasts are being made for the United States surface temperatures at lead times of several seasons. While modest, the skill is significant in that it defies the existence or a 3-week LOP, and so demonstrates the potential for model improvements.     

A combined pyrolysis mass spectrometric and light microscopic study of peatified Calluna wood isolated from raised bog peat deposits

Stem wood of the Angiosperm Calluna vulgaris (Scotch heather), isolated at different depths from a selection of raised bog peat deposits, was chemically characterized using in-source pyrolysis mass spectrometry (Py-MS) and Curie-point pyrolysis gas chromatography mass spectrometry (Py-GC-MS). Light microscopy was performed to relate mass spectrometric characteristics with anatomical features. Peatified wood samples, isolated from increasing depth show a gradual decrease in carbohydrate content. This decrease in anatomically reflected in a selective removal of secondary cell wall material from the fibre-tracheids and wood parenchyma. During prolonged peatification a selective removal of hemicellulose sugars is observed, while a part of the cellulose fraction is preserved. This highly resistant cellulose is mainly located in the secondary cell walls of the vessels. The lignin macromolecule is preserved, but a gradual decrease in syringyl to guaiacyl ratio (S/G) is observed during peatification. Because no increase in catechol and phenolic compounds is observed, we conclude that S/G shifts are due to removal the of syringyl-rich secondary cell wall material and the retention of guaiacyl-rich compound middle lamella. Small chemical changes in the lignin macromolecule involve shifts in oxygen substitutions on the aliphatic side chains of the methoxyphenolics and the occurrence of aromatic acids.     

Fluid inclusion and cathodoluminescence studies on fluorite from the Kerio valley, Kenya

The Kerio valley lies between the Elgeyo escarpment and the Tugen hills which mark the western margin of the Kenya rift valley. The main fluorite deposits are located in the southern part of the valley at Kimwarer, Choff and Kamnaon.Three types of inclusion fillings were identified: Liquid+Vapour, Liquid+Daughter Minerals and Liquid. The L+V type is dominant. Inclusions occur as clusters, trails along the crystal growth zones and as isolated ones. Low salinities, apparently lower than the 5% wt. NaCl equivalent, were established. Homogenization temperatures suggest that fluorite mineralization took place at different stages and at temperatures between 120 and 180 °C. Isolated readings above 180°C may be referring to the original inclusions in limestone. These measurements and the absence of CO₂ in the inclusions, as well as the occurrence of vugs and crustifications with fluorite, suggest that mineralization took place at relatively shallow depths.Emission spectrum lines representing Eu²⁺, Dy³⁺, Tb³⁺ and Sm³⁺ in fluorite were identified. Sm³⁺ was detected only in the pinkish luminescence of veined fluorite, whereas the pinkish zone in banded fluorite contains Tb³⁺. Eu²⁺ which gives the strongest emission lines in the blue part of the visible spectrum, apparently is responsible for the strong blue cathodoluminescence (CL) in fluorite. The dominance of Eu²⁺ peaks further points to the fact that fluorite mineralization in the Kerio valley took place in an environment that was enriched in Lanthanide Rare Earth Elements (LREE). The presence of rare earths and radioactive elements in fluorite points towards their enrichment in the environment of fluorite mineralization. A juvenile origin of mineral forming solutions is proposed.Two generations of fluorite were established: allotriomorphic fluorite, forming the matrix, and the idiomorphic variety, occurring either in barite or in druzes in early fluorite. Barite in turn forms idiomorphic crystals in allotriomorphic fluorite. Relics of calcite occur in both K-feldspars and in early fluorite. Oxides and hydroxides of Fe, Mn, Ti and Al commonly occur in open spaces in fluorite. Of significance is the presence of gold in fluorite. Fluorite mineralization is of hydrothermal origin in the post-Miocene era and was formed as a result of metasomatic replacement of marble and open space fillings.     

Mica beards in three slates: Morphology,formation and bearing on the strain history

Beards are intergrowths of mica, chlorite and quartz or feldspar on detrital grains in weakly metamorphosed sedimentary rocks. The three samples studied contain beards of mica and quartz (or feldspar). Their internal morphology shows a variation in mica orientation related to the external foliation (matrix). Formation occurred during foliation development with a syntaxial growth history. In three dimensions, the beards have oblate shapes, so that they are present in all planes cut parallel to the shortening direction. This indicates flattening strain conditions around the detrital grains during the beard formation.Bulk inhomogeneous shortening, resulting in an anastomosing foliation, can explain the local extension within the plane containing the fold axis and the shortening direction. Concurrently, an approximately constant lenght in the direction of the fold axis is maintained on a regional scale (plane strain). Volume loss probably plays an important role during the formation history.

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Zusammenfassung Glimmerbärte in schwach metamorphen Sedimenten sind syntektonische Verwachsungen von Glimmer, Chlorit, Quarz oder Feldspat auf detritischen Körnern. Die drei hier untersuchten Proben enthalten Bärte aus Hellglimmer und Quarz (oder Feldspat). Die Glimmerorientierung zeigt Variationen in Relation zum umgebenden Schieferungsgefüge (Matrix). Die Bildung der Bärte fand mit syntaxialem Wachstum während der Schieferung statt. Dreidimensional haben die Bärte eine abgeplattete Gestalt, so daß sie in allen Schnittlagen parallel zur Verkürzungsrichtung zu beobachten sind. Dies weist auf plättende Verformung um detritische Körner während der Bildung der Bärte hin.Bulk inhomogeneous shortening führt zu einem linsigen Schieferungsgefüge und kann bei gleichzeitiger Annahme einer nicht volumenkonstanten Deformation als Erklärung für die im Korngefüge beobachtete Dehnung parallel zur Faltenachse herangezogen werden. Im regionalen Maßstab wird aber eine konstante Länge in Richtung der Faltenachse und damit ebene Deformation angenommen.

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Résumé Les barbes de mica sont des intercroissances de quartz (ou feldspath) et de mica sur des grains détritiques dans les roches sédimentaires peu métamorphisées. Elles ont été étudiées dans trois échantillons. Leur morphologie interne montre une variation dans l'orientation du mica en relation avec la schistosité externe (matrice). Leur formation s'est produite pendant le développement de la schistosité, avec une histoire de croissance «syntaxiale». Les barbes ont une forme oblongue en trois dimensions, de sorte qu'elles sont visibles dans toutes les sections parallèles à la direction de raccourcissement. Cela indique, pendant la formation des barbes, l'existence d'un aplatissement autour des grains détritiques.Le raccourcissement non homogène, qui entraîne une foliation anastomosée peut être invoqué, conjointement à une déformation avec perte de volume, pour expliquer l'allongement que présente localement la microstructure parallèlement à l'axe des plis. A l'échelle régionale, toutefois, on admet la constance de la longuer selon la direction des axes et, partant, le caractère plan de la déformation.

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, (Glimmerbärte). Glimmerbärte ( ). — . Glimmerbärte . Glimmerbärte , , . Bulk inhomogeneous shortening , , , . .

     

Large scale, stationary, frontal features in the Benguela Current system

Large scale, stationary features of the Benguela Current system have been observed on satellite infrared images. This paper attempts to establish the most likely dynamical framework required to explain the features. Although the observed features are clearly baroclinic, the wavelength of the 2.2 day period barotropic shelf wave (Buchwald and Adams, 1968, Proceedings of the Royal Society of London, A305, 235–250) fits the observed longshore spatial structure of the features well. The barotropic shelf wave model fails to explain the baroclinic nature and the stationary aspect of the observed features. More observational and theoretical work is necessary to understand the dynamics of these features.     

Selective feeding and grazing rates of oyster (Crassostrea virginica) larvae on natural phytoplankton assemblages

Results of laboratory feeding experiments suggest that oyster (Crassostrea virginica) larvae select small phytoplanktonic organisms (<10 μm) over larger-celled forms from natural estuarine assemblages, but that little selection occurs within the small phytoplankton fraction. Laboratory-reared larvae grazed each of five small-celled phytoplankton groups enumerated (coccoids, centrate diatoms, pennate diatoms, dinoflagellates, and flagellates) at rates proportional to phytoplankton group densities in controls (no larvae added). Larval grazing rates (number of cells removed per larva per hour) were inversely proportional to both larval density and experimental duration.     

Summertime atmospheric circulation in the vicinity of a blue ice area in Queen Maud Land,Antarctica

The surface wind field is an important factor controlling the surface mass balance of Antarctica. This paper focuses on the observed atmospheric circulation during summer of an Antarctic blue ice area in Queen Maud Land. Blue ice areas are characterised by a negative surface mass balance and henceforth provide an interesting location to study the influence of meteorological processes on large local mass balance gradients. During lapse conditions, synoptic forcing determines the surface-layer flow. No significant horizontal temperature gradient with coastal stations could be detected along isobaric surfaces, indicating weak or absent thermal wind. Observations performed at the coastal stations Halley and Georg von Neumayer show the pronounced effects of synoptic forcing. The surface winds in the valley of the blue ice area could be divided into two distinct flow patterns, occurring with about equal frequency during the experiment. Flow type I is associated with cyclonic activity at the coast, resulting in strong easterly winds, precipitation and drifting snow. Flow characteristics inside and outside of the valley are similar during these conditions. Flow type II occurs when a high pressure system develops in the Weddell Sea, weakening the free atmosphere geostrophic winds. A local circulation is able to develop inside the valley of the blue ice area during these tranquil conditions. The transition from flow type II to flow type I is associated with front-like phenomena inside the valley. Some simple theoretical considerations show that surface-layer stability and the upper air geostrophic wind determine the surface flow direction in the valley. Finally, the influence of the observed circulation on the energy and mass balance of the blue ice area is discussed.