Zonal Wavelengths of Planetary Rossby Waves Derived from Hydrographic Transects in the Northeast Atlantic Ocean?     

Eberhard Hagen 《Journal of Oceanography》2005,61(6):1039-1046

Using hydrographic data of three extended zonal sections, which cover the upper 1000 dbar layer along 10°, 21°, and 32°N in the North-East Atlantic between 20° and 45°W, observational evidence is presented for zonal wavelengths of resonantly excited, first mode, long, baroclinic Rossby waves. The amplitudes of associated anomalies in the mass field decrease with increasing offshore distance. The associated zonal wavelengths reach several hundred kilometres and decrease with increasing latitude. Due to the Rossby dispersion, the detected wave patterns slowly propagate westward, somewhat faster in the south than in the north. The results obtained confirm the data sets remotely sensed by satellites, as well as the outcomes of analytical and numerical models.  相似文献   

Benthic organic carbon flux and oxygen penetration reflect different plankton provinces in the Southern Ocean     

Oliver Sachs  Eberhard J. Sauter  Michael Schlüter  Michiel M. Rutgers van der Loeff  Kerstin Jerosch  Ola Holby 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(8):1319-1335

For the investigation of organic carbon fluxes reaching the seafloor, oxygen microprofiles were measured at 145 sites in different sub-regions of the Southern Ocean. At 11 sites, an in situ oxygen microprofiler was deployed for the measurement of oxygen profiles and the calculation of organic carbon fluxes. At four sites, both in situ and ex situ data were determined for high latitudes. Based on this data set as well as on previous published data, a relationship was established for the estimation of fluxes derived by ex situ measured O₂ profiles. The fluxes of labile organic matter range from 0.5 to 37.1 mg C m^?2 d^?1. The high values determined by in situ measurements were observed in the Polar Front region (water depth of more than 4290 m) and are comparable to organic matter fluxes observed for high-productivity, upwelling areas like off West Africa. The oxygen penetration depth, which reflects the long-term organic matter flux to the sediment, was correlated with assemblages of key diatom species. In the Scotia Sea (～3000 m water depth), oxygen penetration depths of less than 15 cm were observed, indicating high benthic organic carbon fluxes. In contrast, the oxic zone extends down to several decimeters in abyssal sediments of the Weddell Sea and the southeastern South Atlantic. The regional pattern of organic carbon fluxes derived from microsensor data suggests that episodic and seasonal sedimentation pulses are important for the carbon supply to the seafloor of the deep Southern Ocean.  相似文献   

IGCP-499 Workshop ＂Depositional Environments of the Gondwanan and Laurasian Devonian＂     

Peter Konigshof Eberhard Schindler Volker Wilde Jurga Lazauskiene M. Namik Yalcin 《《幕》》2006,29(2):135-135

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Two-Dimensional Mapping of the He D<Subscript>3</Subscript>/Hβ Emission Ratio in Solar Prominences     

Eberhard Wiehr  Goetz Stellmacher  Johann Hirzberger 《Solar physics》2007,240(1):25-36

Solar prominences have been simultaneously observed in the integrated light of the He D₃ and the Hβ emissions on two successive days, using the SST on La Palma with its tip-tilt mirror locked on a nearby white-light limb facular grain. The spatial and the temporal variation of the integrated line intensities and their ratio shows mainly two characteristics: (A) Constant emission ratio (even) in regions with substantial intensity variations and (B) varying emission ratio (often) tightly related to intensity structures of the prominence. (A) May be explained by a different number of superposing threads along the line of sight having very similar physical state. (B) Indicates threads with different intrinsic physical states; these may depend on the gas pressure or the inner structure of each thread, i.e., the “packing density,” affecting the penetration of ionizing EUV radiation, which affects the He i level populations and thus the rate of the triplet excitation.  相似文献   

Simulation of oceanic volume transports through Fram Strait 1995–2005     

Kerstin Fieg  Rüdiger Gerdes  Eberhard Fahrbach  Agnieszka Beszczynska-Möller  Ursula Schauer 《Ocean Dynamics》2010,60(3):491-502

We discuss the model representation of volume transports through one of the most climate-relevant ocean passages, the Fram Strait. We compare results from a coupled ocean–sea ice model with different resolutions (∼1/12° and ∼1/4°) and measurements from a mooring array along 79° N. The 1/4° model delivers a realistic mean climate state and realistic net volume transports. However, this model fails to reproduce the observed intense barotropic recirculation that reaches far north in Fram Strait. This recirculation is captured in the higher resolution version of the model. Other differences exist in the circulation over the East Greenland Shelf and in the temperature of Atlantic waters in the Fram Strait region as well as in surface heat fluxes. We find that a combination of high-resolution model results and long-term measurements can improve the interpretation of measured and simulated processes and reduce the uncertainties in exchange rates between Arctic and the North Atlantic.  相似文献   

On the influence of non-Gaussianity on turbulent transport     

Stefan Heinz  Eberhard Schaller 《Boundary-Layer Meteorology》1996,81(2):147-166

Non-Gaussianity effects, first of all the influence of the third and fourth moments of the velocity probability density function, have to be assessed for higher-order closure models of turbulence and Lagrangian modelling of turbulent dispersion in complex flows. Whereas the role and the effects of the third moments are relatively well understood as essential for the explanation of specific observed features of the fully developed convective boundary layer, there are indications that the fourth moments may also be important, but little is known about these moments. Therefore, the effects of non-Gaussianity are considered for the turbulent motion of particles in non-neutral flows without fully developed convection, where the influence of the fourth moments may be expected to be particularly essential. The transport properties of these flows can be characterized by a diffusion coefficient which reflects these effects. It is shown, for different vertical velocity distributions, that the intensity of turbulent transport may be enhanced remarkably by non-Gaussianity. The diffusion coefficient is given as a modification of the Gaussian diffusivity, and this modifying factor is found to be determined to a very good approximation by the normalized fourth moment of the vertical velocity distribution function. This provides better insight into the effect of fourth moments and explains the varying importance of third and fourth moments in different flows.  相似文献   

Thermobarometric data from a fossil zircon partial annealing zone in high pressure–low temperature rocks of eastern and central Crete, Greece     

Manfred R. Brix  Bernhard Stckhert  Eberhard Seidel  Thomas Theye  Stuart N. Thomson  Martina Küster 《Tectonophysics》2002,349(1-4)

A fossil partial annealing zone of fission tracks in zircon is described from high pressure–low temperature (HP–LT) rocks of the Phyllite–Quartzite Unit (PQ) on the island of Crete, Greece. Correlation of regional trends in fission track age populations with independent thermobarometric and microstructural data, and with new experimental annealing results, allows a calibration of this low temperature thermochronological method to a degree hitherto not available from other field examples.The zircon fission track (FT) ages of samples from the PQ across Crete range from original detrital signature through reduced to completely reset. The annealing is the result of a single heating period related to the HP–LT metamorphism with near-peak temperatures lasting for only a few million years some time between 24±1 and 20±1 Ma. In eastern Crete, where rocks have experienced temperatures of 300±50 °C and pressures of 0.8±0.3 GPa, zircon FT ages range from 414±24 to 145±10 Ma. Ages above 300 Ma occur mostly near the east coast of the island in rocks which have not been heated to above ca. 280 °C and probably represent a pre-Variscan source. Track lengths are already indicative of a substantial annealing at this temperature. Most of the zircon FT ages from eastern Crete scatter within error around the stratigraphic age. Samples with apparent zircon FT ages significantly younger than the depositional age are only observed in areas where temperatures exceeded ca. 320 °C. Towards the west, a sudden decrease to very young ages ranging from 17±2 to 18±1 Ma reflects a complete resetting at ca. 350 °C. Short tracks, however, are still observed. Throughout the central and western part of the island, ages are consistently below 22 Ma. Thermobarometric data for this area indicate maximum temperatures of 400±50 °C and pressures of 1±0.3 GPa. Only samples from western Crete, which have been exposed to 400±50 °C, show exclusively long tracks. Consequently, the high temperature limit of the zircon partial annealing zone (ZPAZ) appears to be between 350 and 400 °C.A significant influence of elevated confining pressure on the stability of fission tracks in zircon is ruled out by the results of annealing experiments at 0.5 GPa and at different temperatures, which fit the curves previously obtained by other authors at ambient pressure.  相似文献   

Impact ejecta exceeding lunar escape velocity     

Eberhard Schneider 《Earth, Moon, and Planets》1975,13(1-3):173-184

Microrater frequencies caused by fast (? 3 km s^?1) ejecta have been determined using secondary targets in impact experiments. A primary projectile (steel sphere, diam 1.58 mm, mass 1.64 × 10^?2 g) was shot in Duran glass with a velocity of 4.1 km s^?1 by means of a light gas gun. The angular distribution of the secondary crater number densities shows a primary maximum around 25°, and a secondary maximum at about 60° from the primary target surface. The fraction of mass ejected at velocities of ? 3 km s^?1 is only a factor of 7.5 × 10^?5 of the primary projectile mass. A conservative calculation shows that the contribution of secondary microcraters (caused by fast ejecta) to primary microcrater densities on lunar rock surfaces (caused by interplanetary particles) is on the statistical average below 1% for any lunar surface orientation. Calculation of the interplanetary dust flux enhancement caused by Moon ejecta turned out to be in good agreement with Lunar Explorer 35in situ measurements.  相似文献   

The East Greenland Current and its contribution to the Denmark Strait overflow   总被引：8，自引：1，他引：8  

Rudels  Bert; Fahrbach  Eberhard; Meincke  Jens; Budeus  Gereon; Eriksson  Patrick 《ICES Journal of Marine Science》2002,59(6):1133-1154

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A dense bottom water plume in the western Barents Sea: downstream modification and interannual variability     

Ursula Schauer  Eberhard Fahrbach 《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(12):401

The generation and downstream modification of a cold dense Arctic shelf water plume were studied with moored current meters, thermistor chains and conductivity/temperature sensors deployed from August 1993 to September 1994 south of the Storfjord in the Svalbard Archipelago. These observations are compared to similar time series from 1991/92. In 1993/94, bottom water with temperatures close to the freezing point drained continuously from Storfjord between March and September with a mean speed of 0.14 m s⁻¹. About 1.5 months after the plume front had left the Storfjord, it reached the shelf break, 150 km away. The plume had increased its width from 15 km to about 35 km, but its thickness of 50 m remained almost constant and it left the shelf edge at a similar speed. The increased volume transport and the change of temperature/salinity properties indicate an entrainment of 110% of ambient Atlantic water into the plume on its way from the production area to the shelf edge.The maximum salinity of the cold plume was 0.2 lower in 1993/94 than in 1991/92, whilst the temperature/salinity-range of the surrounding Atlantic water remained unchanged. Probably as a dynamic consequence, the speed of the plume was considerably lower in 1993/94. The lower salinity of the plume in 1993/94 is a result of both the 30% less ice formation in Storfjord, caused by lower heat flux and less open water, and a lower surface salinity at the beginning of ice formation. During 1993/94, the Storfjord plume was too light to sink below 700 m.  相似文献