Steady flows in active regions observed with the HeI 10830 Å line     

Bruce W. Lites  Stephen L. Keil  Göran B. Scharmer  Arne A. Wyller 《Solar physics》1985,97(1):35-49

We show that the He i 10830 A line gives reliable Doppler shift measurements in the upper chromosphere above active regions. Persistent flow patterns in active regions observed near the solar limb show features previously noted in Dopplergrams using the Civ transition region ultraviolet emission line. Unlike the Civ measurements, however, the He i absorption shows a strong correlation with the line-of-sight velocity images in certain regions of some active regions.Operated by the Association of Universities for Research in Astronomy, Inc., under contract AST 78-17292 with the United States National Science Foundation.The National Center for Atmospheric Research is operated by the University Corporation for Atmospheric Research under sponsorship of the National Science Foundation.Visiting Astronomers, Sacramento Peak Observatory.  相似文献   

Mesoscale activity in the North Sea as seen in ensemble simulations     

Arne Melsom 《Ocean Dynamics》2005,55(3-4):338-350

A set of two simulation ensembles of the ocean circulation in the North Sea, the Skagerrak and bordering seas has been run for the ten year period that started in January 1992. The ensembles differed only in the horizontal grid resolution. The main purposes of this investigation are (1) to quantify the variability that can be expected in multi-year simulations due to noise-like perturbations in the initial fields, and (2) to examine the robustness of model results for mesoscale features that form on the front between the Norwegian Coastal Current and water masses that are of an Atlantic Ocean origin. It is shown that the model resolution has a substantial impact on the ensemble variability, and that the role of small perturbations become more significant as the grid mesh is refined. Nevertheless, it is demonstrated that in a region to the west of the southern tip of Norway, eddies are occasionally found in the same positions at the same time in the results from all members of the ensembles. This is particularly the case in the aftermath of outbreak events of low salinity water masses from the Skagerrak into the North Sea.  相似文献   

Holocene recolonization and extinction of the pond turtle, Emys orbicularis (L., 1758), in Europe     

Robert S. Sommer  Arne Persson  Nina Wieseke  Uwe Fritz 《Quaternary Science Reviews》2007,26(25-28):3099-3107

We reconstruct the Holocene range fluctuations of the European pond turtle (Emys orbicularis) for northern and Central Europe. Based on 529 subfossil records and radiocarbon dating of critical finds, we provide evidence that E. orbicularis experienced a rapid range expansion with Holocene warming. Phylogeographic data argue for a colonization of northern and Central Europe from a glacial refuge located in the south-eastern Balkans. Already in the Late Preboreal (9100–8600 cal BC) the species occurred in northern Central Europe and was widespread in Denmark and southern Sweden (Skåne) during the Boreal (8600–7100 cal BC). The maximum range extension occurred during the Holocene climatic optimum (Atlantic: 7100–3750 cal BC), with records in southern England, middle Sweden, and northern Estonia. After the early Subboreal (3750–1750 cal BC) northern populations collapsed, coinciding with a climatic cooling and oceanization. Northern populations were most likely established via long distance dispersal (rafting using rivers debouching in the North and Baltic Seas); after northern Europe was reached, a minimum dispersal of 50 km per 100 years may be hypothesized for the Boreal.  相似文献   

A robust approach to global problems in physical geodesy     

Arne Bjerhammar 《Journal of Geodesy》1985,59(4):303-315

A technique for renormalization of integral equations is used for obtaining very robust solutions. The number of multiplications used for inverting the integral equations can be reduced dramatically and mostly only weighted means will be needed. Theoretical gain in computer time might be up to 100 000 times for the most favourable cases when using 1000 unknowns. (Practical gains will be considerably less.) Solutions have been obtained with increased accuracy compared to the classical technique over integral equations. Surface elements might be of arbitrary size but the method is optimal for a global approach with equal area elements. The solutions were found strictly invariant with respect to the depth to the internal sphere, when using simpler models. Applications in surveying are possible after some modifications. Renormalization of integral equation has been widely used in the theory of quantum field.  相似文献   

Electron microscope study of peridotite xenoliths in kimberlites     

Arne Olsen  Tore Birkeland 《Contributions to Mineralogy and Petrology》1973,42(2):147-157

Dislocation structures in naturally deformed olivine from garnet peridotite xenoliths from South African kimberlites have been studied by electron microscopy. The substructure consists mainly of straight subboundaries of dislocations with Burgers vectors [001]. Most of the dislocations have both edge and screw components, and the slip planes are mainly (100). The dislocation density between the subboundaries is low.The slip planes in olivine are discussed in relation to the olivine structure. The observed dislocation structures seem to indicate that the large difference in strain rate between natural and experimental deformation will produce a difference in the slip mechanisms.The nature of the deformation lamellae visible in optical microscope is discussed.  相似文献   

Chemical characterization of sub-micrometer aerosol particles in the tropical Atlantic Ocean: marine and biomass burning influences     

Manuela van Pinxteren  Björn Fiedler  Dominik van Pinxteren  Yoshiteru Iinuma  Arne Körtzinger  Hartmut Herrmann 《Journal of Atmospheric Chemistry》2015,72(2):105-125

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Mesozoic exhumation history and palaeolandscape of the Iberian Massif in eastern Galicia from apatite fission-track and (U+Th)/He data     

R. W. Grobe  J. Alvarez-Marrón  U. A. Glasmacher  F. M. Stuart 《International Journal of Earth Sciences》2014,103(2):539-561

Apatite fission-track (AFT) and (U+Th)/He (AHe) data, combined with time–temperature inverse modelling, reveal the cooling and exhumation history of the Iberian Massif in eastern Galicia since the Mesozoic. The continuous cooling at various rates correlates with variation of tectonic boundary conditions in the adjacent continental margins. The data provide constraints on the 10⁷ timescale longevity of a relict paleolandscape. AFT ages range from 68 to 174 Ma with mean track lengths of 10.7 ± 2.6 to 12.6 ± 1.8 μm, and AHe ages range from 73 to 147 Ma. Fastest exhumation (≈0.25 km/Ma) occurred during the Late Jurassic to Early Cretaceous main episode of rifting in the adjacent western and northern margins. Exhumation rates have decreased since then and have been approximately one order of magnitude lower. Across inland Galicia, the AFT data are consistent with Early Cretaceous movement on post-Variscan NE trending faults. This is coeval with an extensional episode offshore. The AHe data in this region indicate less than 1.7 km of denudation in the last 100 Ma. This low exhumation suggests the attainment of a mature landscape during Late Cretaceous post-rift tectonic stability, whose remains are still preserved. The low and steady rate of denudation prevailed across inland Galicia despite minor N–S shortening in the northern margin since ≈45 Ma ago. In north Galicia, rock uplift in response to NW strike-slip faulting since Early Oligocene to Early Miocene has caused insufficient exhumation (<3 km) to remove the Mesozoic cooling signal recorded by the AFT data.  相似文献