Predicting Nocturnal Wind and Temperature Profiles Based on External Forcing Parameters   总被引：1，自引：1，他引：0  

J. M. M. Donda  B. J. H. Van de Wiel  F. C. Bosveld  F. Beyrich  G. J. F. van Heijst  H. J. H. Clercx 《Boundary-Layer Meteorology》2013,146(1):103-117

We introduce a simple, physically consistent method to predict nocturnal wind and temperature profiles from external forcing parameters such as the geostrophic wind. As an indicator of the radiative ??forcing?? the net longwave radiative cooling is used as a proxy. Surface fluxes are expressed in terms of these parameters by coupling an Ekman model to a rudimentary surface energy balance. Additionally the model assumes validity of Monin-Obukhov similarity in order to predict near-surface wind and temperature profiles up to a height equal to the Obukhov length. The predictions are validated against an independent dataset that covers 11-years of observations at Cabauw, The Netherlands. It is shown that the characteristic profiles in response to external forcings are well-captured by the conceptual model. For this period the observational climatology is in close agreement with ECMWF re-analysis data. As such, the conceptual model provides an alternative tool to giving a first-order estimate of the nocturnal wind and temperature profile near the surface in cases when advanced numerical or observational infrastructure is not available.  相似文献   

The formation of IIE iron meteorites investigated by the chondrule‐bearing Mont Dieu meteorite          下载免费PDF全文

N. Van Roosbroek  V. Debaille  L. Pittarello  S. Goderis  M. Humayun  L. Hecht  F. Jourdan  M. J. Spicuzza  F. Vanhaecke  Ph. Claeys 《Meteoritics & planetary science》2015,50(7):1173-1196

A 435 kg piece of the Mont Dieu iron meteorite (MD) contains cm‐sized silicate inclusions. Based on the concentration of Ni, Ga, Ge, and Ir (8.59 ± 0.32 wt%, 25.4 ± 0.9 ppm, 61 ± 2 ppm, 7.1 ± 0.4 ppm, respectively) in the metal host, this piece can be classified as a IIE nonmagmatic iron. The silicate inclusions possess a chondritic mineralogy and relict chondrules occur throughout the inclusions. Major element analysis, oxygen isotopic analysis (Δ¹⁷O = 0.71 ± 0.02‰), and mean Fa and Fs molar contents (Fa_{15.7 ± 0.4} and Fs_{14.4 ± 0.5}) indicate that MD originated as an H chondrite. Because of strong similarities with Netschaëvo IIE, MD can be classified in the most primitive subgroup of the IIE sequence. ⁴⁰Ar/³⁹Ar ages of 4536 ± 59 Ma and 4494 ± 95 Ma obtained on pyroxene and plagioclase inclusions show that MD belongs to the old (~4.5 Ga) group of IIE iron meteorites and that it has not been perturbed by any subsequent heating event following its formation. The primitive character of MD sheds light on the nature of its formation process, its thermal history, and the evolution of its parent body.  相似文献   

A search for shocked quartz grains in the Allerød‐Younger Dryas boundary layer          下载免费PDF全文

Annelies Van Hoesel  Wim Z. Hoek  Gillian M. Pennock  Knut Kaiser  Oliver Plümper  Michal Jankowski  Maartje F. Hamers  Norbert Schlaak  Mathias Küster  Alexander V. Andronikov  Martyn R. Drury 《Meteoritics & planetary science》2015,50(3):483-498

The Younger Dryas impact hypothesis suggests that multiple airbursts or extraterrestrial impacts occurring at the end of the Allerød interstadial resulted in the Younger Dryas cold period. So far, no reproducible, diagnostic evidence has, however, been reported. Quartz grains containing planar deformation features (known as shocked quartz grains), are considered a reliable indicator for the occurrence of an extraterrestrial impact when found in a geological setting. Although alleged shocked quartz grains have been reported at a possible Allerød‐Younger Dryas boundary layer in Venezuela, the identification of shocked quartz in this layer is ambiguous. To test whether shocked quartz is indeed present in the proposed impact layer, we investigated the quartz fraction of multiple Allerød‐Younger Dryas boundary layers from Europe and North America, where proposed impact markers have been reported. Grains were analyzed using a combination of light and electron microscopy techniques. All samples contained a variable amount of quartz grains with (sub)planar microstructures, often tectonic deformation lamellae. A total of one quartz grain containing planar deformation features was found in our samples. This shocked quartz grain comes from the Usselo palaeosol at Geldrop Aalsterhut, the Netherlands. Scanning electron microscopy cathodoluminescence imaging and transmission electron microscopy imaging, however, show that the planar deformation features in this grain are healed and thus likely to be older than the Allerød‐Younger Dryas boundary. We suggest that this grain was possibly eroded from an older crater or distal ejecta layer and later redeposited in the European sandbelt. The single shocked quartz grain at this moment thus cannot be used to support the Younger Dryas impact hypothesis.  相似文献   

Systematic documentation of landslide events in Limbe area (Mt Cameroon Volcano,SW Cameroon): geometry,controlling, and triggering factors     

V. B. Che  M. Kervyn  G. G. J. Ernst  P. Trefois  S. Ayonghe  P. Jacobs  E. Van Ranst  C. E. Suh 《Natural Hazards》2011,59(1):47-74

Limbe town and surrounding areas, on the SE foot slopes of the active Mt Cameroon Volcano, have experienced numerous small-scale shallow landslides within the last 20 years. These resulted in the loss of ~30 lives and significant damage to farmland and properties. Landslides and their scars are identified in the field, and their geometry systematically measured to construct a landslide inventory map for the study area. Specific landslides are investigated in detail to identify site-specific controlling and triggering factors. This is to constrain key input parameters and their variability for subsequent susceptibility and risk modeling, for immediate local and regional applications in land-use planning. It will also enable a rapid exploration of remediation strategies that are currently lacking in the SW and NW regions of Cameroon. Typical slides within the study area are small-scale, shallow, translational earth, and debris slides though some rotational earth slides were also documented. The depletion zones have mean widths of 22 m ± 16.7 m and lengths of 25 ± 23 standard deviation. Estimated aerial extents of landslide scars and volume of generated debris range from 10¹ to 10⁴ m² and 2 to 5 × 10⁴ m³, respectively. A key finding is that most slope instabilities within the study area are associated with and appear to be exacerbated by man-made factors such as excavation, anarchical construction, and deforestation of steep slopes. High intensity rainfall notably during localized storms is the principal triggering factor identified so far. The findings from this case study have relevance to understanding some key aspects of locally devastating slope instabilities that commonly occur on intensely weathered steep terrains across subtropical Africa and in the subtropics worldwide and affecting an ever denser and most vulnerable population.  相似文献   

The first ML scale for North of Vietnam     

Le Minh Nguyen  Ting-Li Lin  Yih-Min Wu  Bor-Shouh Huang  Chien-Hsin Chang  Win-Gee Huang  Tu Son Le  Van Toan Dinh 《Journal of Asian Earth Sciences》2011,40(1):279-286

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The Montalet granite, Montagne Noire, France: An Early Permian syn-extensional pluton as evidenced by new U-Th-Pb data on zircon and monazite     

Jean-Charles Poilvet  Marc Poujol  Pavel Pitra  Jean Van Den Driessche  Jean-Louis Paquette 《Comptes Rendus Geoscience》2011,343(7):454-461

Dating the magmatism in the Montagne Noire gneiss dome in the southern French Massif Central is a key point for understanding the Late Palaeozoic evolution of this part of the Variscan belt, which is characterised by compressive tectonics during the Carboniferous and extensional tectonics during Stephanian-Permian times. The Montalet granite crops out in the north-western part of the dome and was first considered as an early syntectonic intrusion related to compressive deformation. More recently, it has been dated at 327 Ma and considered as contemporaneous with the diapiric ascent of the Montagne Noire gneiss dome before the Stephanian-Permian extension. We show that in fact, this pluton was emplaced 294 ± 1 Ma ago and is therefore contemporaneous with the Stephanian-Permian extension. This age is consistent with the interpretation of the Montagne Noire Massif as an extensional gneiss dome.  相似文献   

Pliocene to Recent shallow-water contourite deposits on the shelf and shelf edge off south-western Mallorca, Spain   总被引：2，自引：2，他引：0  

Thomas Philippe Vandorpe  David Van Rooij  Dorrik A. V. Stow  Jean-Pierre Henriet 《Geo-Marine Letters》2011,31(5-6):391-403

This paper presents evidence for the presence of shallow-water contourite drifts on the south-western shelf and shelf edge off Mallorca in water depths between 150 and 275?m. These are called the Mallorca contourite depositional system (CDS). The elongate-mounded shallow-water CDS in this area is ascribed to an offshoot of the Balearic Current, which flows north to south through the Mallorca Channel as part of the overall thermohaline circulation in the Mediterranean Sea. Drift geometry suggests that the north?Csouth current is deflected into an east?Cwest flow pattern by interaction with a marked seafloor bathymetry, associated with major fault displacement. Four seismic units separated by three prominent discontinuities can be identified. The three internal discontinuities are correlated to large-scale basin-wide events: the lower Pliocene revolution (4.2?Ma), the upper Pliocene revolution (2.4?Ma) and the mid-Pleistocene revolution (0.9?Ma). The Plio-Quaternary succession has been deposited on top of a Miocene reef, which serves as an acoustic basement and is affected by a large fault, offsetting the basement on average by 150?m. Marked erosional features throughout and further incision of the Sant Jordi Channel along the basement fault in the Pleistocene deposits indicate stronger currents in this period. The Pleistocene deposits also show a pronounced cyclicity, which is tentatively ascribed to climatic variations and the effects of eustatic sea-level fluctuation over the south-western Mallorca shelf at that time.  相似文献   

Deep-water Circulation: Processes & Products (16�C18 June 2010, Baiona): introduction and future challenges     

Francisco Javier Hern��ndez-Molina  Dorrik A. V. Stow  Estefan��a Llave  Michele Rebesco  Gemma Ercilla  David Van Rooij  Anxo Mena  Juan-Tom��s V��zquez  Antje H. L. Voelker 《Geo-Marine Letters》2011,31(5-6):285-300

Deep-water circulation is a critical part of the global conveyor belt that regulates Earth??s climate. The bottom (contour)-current component of this circulation is of key significance in shaping the deep seafloor through erosion, transport, and deposition. As a result, there exists a high variety of large-scale erosional and depositional features (drifts) that together form more complex contourite depositional systems on continental slopes and rises as well as in ocean basins, generated by different water masses flowing at different depths and at different speeds either in the same or in opposite directions. Yet, the nature of these deep-water processes and the deposited contourites is still poorly understood in detail. Their ultimate decoding will undoubtedly yield information of fundamental importance to the earth and ocean sciences. The international congress Deep-water Circulation: Processes & Products was held from 16?C18 June 2010 in Baiona, Spain, hosted by the University of Vigo. Volume 31(5/6) of Geo-Marine Letters is a special double issue containing 17 selected contributions from the congress, guest edited by F.J. Hernández-Molina, D.A.V. Stow, E. Llave, M. Rebesco, G. Ercilla, D. Van Rooij, A. Mena, J.-T. Vázquez and A.H.L. Voelker. The papers and discussions at the congress and the articles in this special issue provide a truly multidisciplinary perspective of interest to both academic and industrial participants, contributing to the advancement of knowledge on deep-water bottom circulation and related processes, as well as contourite sedimentation. The multidisciplinary contributions (including geomorphology, tectonics, stratigraphy, sedimentology, paleoceanography, physical oceanography, and deep-water ecology) have demonstrated that advances in paleoceanographic reconstructions and our understanding of the ocean??s role in the global climate system depend largely on the feedbacks among disciplines. New insights into the link between the biota of deep-water ecosystems and bottom currents confirm the need for this field to be investigated and mapped in detail. Likewise, it is confirmed that deep-water contourites are not only of academic interest but also potential resources of economic value. Cumulatively, both the congress and the present volume serve to demonstrate that the role of bottom currents in shaping the seafloor has to date been generally underestimated, and that our understanding of such systems is still in its infancy. Future research on contourites, using new and more advanced techniques, should focus on a more detailed visualization of water-mass circulation and its variability, in order to decipher the physical processes involved and the associations between drifts and other common bedforms. Moreover, contourite facies models should be better established, including their associations with other deep-water sedimentary environments both in modern and ancient submarine domains. The rapid increase in deep-water exploration and the new deep-water technologies available to the oil industry and academic institutions will undoubtedly lead to spectacular advances in contourite research in terms of processes, morphology, sediment stacking patterns, facies, and their relationships with other deep-marine depositional systems.  相似文献   

Response of zooplankton to improving water quality in the Scheldt estuary (Belgium)     

B. Mialet  J. Gouzou  F. Azémar  T. Maris  C. Sossou  N. Toumi  S. Van Damme  P. Meire  M. Tackx 《Estuarine, Coastal and Shelf Science》2011

Data obtained from 14 years of monthly samplings (1996–2009) were used to investigate the response of the crustacean zooplankton community to improving water quality in the Scheldt estuary. A strong reduction of poor water quality indicators, such as NH₄⁺ and BOD₅, as well as an increase in oxygen and in chlorophyll a concentrations were observed during the study period. During the study period, important changes were observed in the zooplankton community composition and spatial distribution. From 2007 onwards, most of the calanoid population, previously mainly found in the brackish water reach of the estuary, moved to the freshwater, where they reached higher abundances than previously observed. Simultaneously, cyclopoids populations strongly decreased in freshwater while cladocerans did not change their abundance, except during years with high chlorophyll a concentrations. Redundancy analyses (RDA) showed that the variability within the calanoid population can be explained by the improvement in water quality. Variability within the cyclopoids and cladoceran community is mainly explained by chlorinity and chlorophyll a concentrations. Their presence in the most polluted upstream area until 2007 suggests they are more tolerant to poor water quality than calanoids. Several hypotheses to explain the disappearance of cyclopoids after the move of calanoids to the freshwater are presented and discussed.  相似文献   

Biogeochemistry and carbon mass balance of a coccolithophore bloom in the northern Bay of Biscay (June 2006)     

J. Harlay  L. ChouC. De Bodt  N. Van OostendeJ. Piontek  K. SuykensA. Engel  K. SabbeS. Groom  B. DelilleA.V. Borges 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(2):111-127

Primary production (PP), calcification (CAL), bacterial production (BP) and dark community respiration (DCR) were measured along with a set of various biogeochemical variables, in early June 2006, at several stations at the shelf break of the northern Bay of Biscay. The cruise was carried out after the main spring diatom bloom that, based on the analysis of a time-series of remotely sensed chlorophyll-a (Chl-a), peaked in mid-April. Remotely sensed sea surface temperature (SST) indicated the occurrence of enhanced vertical mixing (due to internal tides) at the continental slope, while adjacent waters on the continental shelf were stratified, as confirmed by vertical profiles of temperature acquired during the cruise. The surface layer of the stratified water masses (on the continental shelf) was depleted of inorganic nutrients. Dissolved silicate (DSi) levels probably did not allow significant diatom development. We hypothesize that mixing at the continental slope allowed the injection of inorganic nutrients that triggered the blooming of mixed phytoplanktonic communities dominated by coccolithophores (Emiliania huxleyi) that were favoured with regards to diatoms due to the low DSi levels. Based on this conceptual frame, we used an indicator of vertical stratification to classify the different sampled stations, and to reconstruct the possible evolution of the bloom from the onset at the continental slope (triggered by vertical mixing) through its development as the water mass was advected on-shelf and stratified. We also established a carbon mass balance at each station by integrating in the photic layer PP, CAL and DCR. This allowed computation at each station of the contribution of PP, CAL and DCR to CO₂ fluxes in the photic layer, and how they changed from one station to another along the sequence of bloom development (as traced by the stratification indicator). This also showed a shift from net autotrophy to net heterotrophy as the water mass aged (stratified), and suggested the importance of extracellular production of carbon to sustain the bacterial demand in the photic and aphotic layers.  相似文献