Dynamic features in the western Baltic Sea investigated using NOAA-AVHRR data

Summary The western part of the Baltic Sea is a shallow transition area which is characterized by the water exchange between the Baltic and the North Sea. The dynamic processes in this area are forced by sea-level differences between the North Sea and Baltic Sea as well as by local wind and freshwater input. The response patterns are modified by Earth's rotation, bathymetric structures and the alignment of the coast. Series of satellite images permit synoptical views of these pattern and their temporal and spatial development.Sea surface temperature maps derived from infrared data supplied by the National Oceanic and Atmospheric Administration (NOAA) satellite-borne Advanced Very High Resolution Radiometer (AVHRR) are used to show various features like upwelling filaments and eddies.The River Oder discharges into the Pomeranian Bight is the main source of freshwater input into the western Baltic. The variability of this inflow and of the affected coastal seas is being presented in relation to the prevailing meteorological conditions.

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Dynamische Besonderheiten in der westlichen Ostsee untersucht anhand von NOAA-AVHRR-Daten

Zusammenfassung Die westliche Ostsee ist ein flaches Übergangsgebiet, das durch den Wasseraustausch zwischen Nord- und Ostsee charakterisiert ist. Die dynamischen Prozesse werden in diesem Gebiet durch Wasserstandsdifferenzen zwischen Nord- und Ostsee, durch den lokalen Wind und die Süßwasserzufuhr getrieben. Die Reaktionsmuster werden modifiziert durch die Erdrotation, die Bathymetrie und den Küstenverlauf.Serien von Satellitendaten gestatten die synoptische Betrachtung dieser Muster und ihrer zeitlichen und räumlichen Entwicklung.Karten der Wasseroberflächentemperatur (SST), abgeleitet aus Infrarotdaten des Advanced Very High Resolution Radiometer (AVHRR), werden genutzt, um verschiedene Strukturen wie Auftrieb, Filamente und Wirbel zu präsentieren. Das Radiometer wird durch die National Oceanic and Atmospheric Administration (NOAA) auf Wettersatelliten betrieben.Der Flußeintrag der Oder in die Pommersche Bucht ist die bedeutendste Süßwasserzufuhr in die westliche Ostsee. Die Veränderlichkeit des Einstroms und die beeinflußten Gebiete sind in Abhängigkeit von den meteorologischen Bedingungen dargestellt.

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Recherche du caractéristiques dynamiques en mer Baltique ouest á l'aide de données NOAA-AVHRR

Résumé La partie ouest de la mer Baltique est une zone de transition de profondeur réduite, caractérisée par un échange des eaux entre la mer du Nord et la mer Baltique.Dans cette zone, les processus dynamiques proviennent des différences de niveau de la mer du Nord et de la mer Baltique, des vents locaux et de l'apport en eau douce. Les modèles créés sont modifiés à partir de la rotation terrestre, de la bathymétrie et de la morphologie côtière.Les données satellite permettent d'établir une étude synoptique de ces processus dans l'ensemble de la zone ainsi que leur développement spatio-temporel au moyen de séries.Des cartes de température superficielle (SST) obtenues à partir des données radiométriques infrarouges AVHRR (Advanced Very High Resolution Radiometer) sont utilisées pour présenter des exemples SST caractéristiques de résultats de processus dynamiques de l'ouest de la mer Baltique. Les données radiométriques proviennent du National Oceanic and Atmospheric Administration (NOAA) à partir de satellites météorologiques.La dépendance des développements spatio-temporels de modèles en fonction des conditions météorologiques est discutée à partir de scènes et de séries particulières.Des exemples d'upwelling devant les côtes allemandes, suédoises et polonaises ainsi que des fronts, des filaments et des tourbillons sont présentés.La plus grande partie de l'apport en eau douce à l'ouest de la mer Baltique provient du fleuve Oder, en baie de Poméranie. L'influence des facteurs météorologiques sur la variation de ce déversement et sur les zones influencées est présentée.

     

On the existence of a relation between the Kolmogoroff and von Kármán constants

A model is described, in which the mean vertical wind profile and turbulence spectra at different heights are calculated for a turbulent boundary layer without thermal stratification. The model makes use of Heisenberg's formula for the transfer of turbulent energy and is based on the assumption of a constant shearing stress in that boundary layer. As a result, a logarithmic wind profile follows with 0.39 as the value of von Kármán's constant, which is — in this model — strongly related to the inertial subrange of the turbulent energy spectra and therefore to the Kolmogoroff constant.This paper is based on studies done by the author during a one-year visit to CSIRO Division of Meteorological Physics, Aspendale, Australia, and was presented at the AGARD Specialists Meeting on The Aerodynamics of Atmospheric Shear Flows sponsored by the Fluid Dynamics Panel at Munich, Germany, during 15–17 Sept. 1969.     

Volume diffusion of Ytterbium in YAG: thin-film experiments and combined TEM–RBS analysis

In this study, we address volume diffusion of ytterbium in yttrium aluminum garnet (YAG) using thin-film single crystal diffusion couples. We employ analytical transmission electron microscopy (ATEM) as a tool for combined microstructural and microchemical analysis and compare the results to Rutherford backscattering (RBS) analysis. Given the high spatial resolution of the method, we focus on microstructural changes of the thin-film diffusant source during the diffusion anneal. We evaluate the potential influence of the associated changes in its transport properties on the evolution of concentration profiles in the single crystal substrate. This approach allows us to test the reliability of determination of volume diffusion coefficients from thin-film diffusion experiments. We found that for the chosen experimental setting, the influence of thin-film re-crystallization is small when compared with the experimental uncertainty and good estimates for the volume diffusion coefficients of Yb in YAG can be obtained using standard assumptions. Both Yb-concentration profiles analyzed with ATEM and with RBS give similar results. At 1,450°C and 1 bar, we infer log D _Yb (m²/s) values of −19.37 ± 0.07 (TEM) and −19.84 ± 0.02 (RBS). Although the change in thin-film transport properties associated with successive crystallization during the diffusion anneal does not play a major role for our experimental setup, this effect cannot generally be ignored.     

Halo streams in the solar neighborhood

The phase-space structure of our Galaxy holds the key to understand and reconstruct its formation. The ΛCDM model predicts a richly structured phase-space distribution of dark matter and (halo) stars, consisting of streams of particles torn from their progenitors during the process of hierarchical merging. While such streams quickly loose their spatial coherence in the process of phase mixing, the individual stars keep their common origin imprinted into their kinematic and chemical properties, allowing the recovery of the Galaxy’s individual “building blocks”. The field of Galactic Archeology has witnessed a dramatic boost over the last decade, thanks to the increasing quality and size of available data sets. This is especially true for the solar neighborhood, a volume of 1–2 kpc around the sun, where large scale surveys like SDSS/SEGUE continue to reveal the full 6D phase-space information of thousands of halo stars. In this review, I summarize the discoveries of stellar halo streams made so far and give a theoretical overview over the search strategies imployed. This article is intended as an introduction to researchers new to the field, but also as a reference illustrating the achievements made so far. I conclude that disentangling the individual fragments from which the Milky Way was built requires more precise data that will ultimately be delivered by the Gaia mission.     

Northwest Africa 1500: Plagioclase‐bearing monomict ureilite or ungrouped achondrite?

Abstract— Northwest Africa (NWA) 1500 is an ultramafic meteorite dominated by coarse (?100–500 μm) olivine (95–96%), augite (2–3%), and chromite (0.6–1.6%) in an equilibrated texture. Plagioclase (0.7–1.8%) occurs as poikilitic grains (up to ?3 mm) in vein‐like areas that have concentrations of augite and minor orthopyroxene. Other phases are Cl‐apatite, metal, sulfide, and graphite. Olivine ranges from Fo 65–73, with a strong peak at Fo 68–69. Most grains are reversezoned, and also have ?10–30 μm reduction rims. In terms of its dominant mineralogy and texture, NWA 1500 resembles the majority of monomict ureilites. However, it is more ferroan than known ureilites (Fo ≥75) and other mineral compositional parameters are out of the ureilite range as well. Furthermore, neither apatite nor plagioclase have ever been observed, and chromite is rare in monomict ureilites. Nevertheless, this meteorite may be petrologically related to the rare augite‐bearing ureilites and represent a previously unsampled part of the ureilite parent body (UPB). The Mn/Mg ratio of its olivine and textural features of its pyroxenes are consistent with this interpretation. However, its petrogenesis differs from that of known augite‐bearing ureilites in that: 1) it formed under more oxidized conditions; 2) plagioclase appeared before orthopyroxene in its crystallization sequence; and 3) it equilibrated to significantly lower temperatures (800–1000 °C, from two‐pyroxene and olivine‐chromite thermometry). Formation under more oxidized conditions and the appearance of plagioclase before orthopyroxene could be explained if it formed at a greater depth on the UPB than previously sampled. However, its significantly different thermal history (compared to ureilites) may more plausibly be explained if it formed on a different parent body. This conclusion is consistent with its oxygen isotopic composition, which suggests that it is an ungrouped achondrite. Nevertheless, the parent body of NWA 1500 may have been compositionally and petrologically similar to the UPB, and may have had a similar differentiation history.     

The influence of Hall drift on the magnetic fields of neutron stars

We consider the evolution of magnetic fields under the influence of Hall drift and Ohmic decay. The governing equation is solved numerically, in a spherical shell with   r _i / r _o = 0.75  . Starting with simple free-decay modes as initial conditions, we then consider the subsequent evolution. The Hall effect induces so-called helicoidal oscillations, in which energy is redistributed among the different modes. We find that the amplitude of these oscillations can be quite substantial, with some of the higher harmonics becoming comparable with the original field. Nevertheless, this transfer of energy to the higher harmonics is not sufficient to accelerate significantly the decay of the original field, at least not at the   R _B = O (100)  parameter values accessible to us, where this Hall parameter   R _B   measures the ratio of the Ohmic time-scale to the Hall time-scale. We do find clear evidence though of increasingly fine structures developing for increasingly large   R _B   , suggesting that perhaps this Hall-induced cascade to ever-shorter length-scales is eventually sufficiently vigorous to enhance the decay of the original field. Finally, the implications for the evolution of neutron star magnetic fields are discussed.     

Advances in radiative transfer

This review describes advances in radiative transfer theory since about 1985. We stress fundamental aspects and emphasize modern methods for the numerical solution of the transfer equation for spatially multidimensional problems, for both unpolarized and polarized radiation. We restrict the discussion to two-level atoms with noninverted populations for given temperature, density and velocity fields. Unfortunately this article was originally published with typesetter's errors: The correct publication date was 25 February 2006, not 3 January 2006. The content was not in the final form. The publishers wish to apologize for this mistake. The online version of the original version can be found at /10.1007/s00159-005-0025-8.