The relative importance of ejections and sweeps to momentum transfer in the atmospheric boundary layer     

Gabriel Katul  Davide Poggi  Daniela Cava  John Finnigan 《Boundary-Layer Meteorology》2006,120(3):367-375

Using an incomplete third-order cumulant expansion method (ICEM) and standard second-order closure principles, we show that the imbalance in the stress contribution of sweeps and ejections to momentum transfer (ΔS _o ) can be predicted from measured profiles of the Reynolds stress and the longitudinal velocity standard deviation for different boundary-layer regions. The ICEM approximation is independently verified using flume data, atmospheric surface layer measurements above grass and ice-sheet surfaces, and within the canopy sublayer of maturing Loblolly pine and alpine hardwood forests. The model skill for discriminating whether sweeps or ejections dominate momentum transfer (e.g. the sign of ΔS _o ) agrees well with wind-tunnel measurements in the outer and surface layers, and flume measurements within the canopy sublayer for both sparse and dense vegetation. The broader impact of this work is that the “genesis” of the imbalance in ΔS _o is primarily governed by how boundary conditions impact first and second moments.  相似文献   

Fluidization and injection in the deep-water sandstones of the Eocene Alba Formation (UK North Sea)   总被引：4，自引：0，他引：4  

Davide Duranti  Andrew Hurst 《Sedimentology》2004,51(3):503-529

The Nauchlan Member of the Late Eocene Alba Formation (UK North Sea) consists of a deep‐water channel fill that was extensively modified by post‐depositional sand remobilization and injection. Sandstone textures, facies associations and the geometry of the channel fill were affected. A suite of sand‐rich facies was produced by large‐scale fluidization and injection within the channel fill and above it. These facies, termed here unstratified facies, are characterized by the absence of stratification surfaces and by discordant relationships with bedding in the adjacent succession. They reflect variable degrees of disruption of the primary sedimentary structures caused by escaping pore fluid, the velocity of which is estimated at least in the order of 0·1 ms^?1. Adjacent mudstones were severely disrupted by hydraulic fracturing, and fragments of fractured mudstone were incorporated into the fluidized sand. Average porosity was decreased in the sandstones affected by fluidization. Two main phases of sand injection are inferred to occur at different burial depths. A shallow burial phase (below 100 m) produced thin dykes with ptygmatic folds. The second phase occurred at the boundary between Eocene and Oligocene (≈ 300 m burial depth) and resulted in large‐scale tabular wing‐like dykes that project from the edges of the channel fill. The significant pore‐fluid overpressure, which was required to hydraulically fracture the thick mudstone seal and to fluidize the large volume of sand, was likely to be built up by static liquefaction of the source sand and was possibly enhanced by hydrocarbon gas influx.  相似文献   

Application of newly developed ensemble machine learning models for daily suspended sediment load prediction and related uncertainty analysis     

Ahmad Sharafati  Seyed Babak Haji Seyed Asadollah  Davide Motta 《水文科学杂志》2020,65(12):2022-2042

ABSTRACT

Ensemble machine learning models have been widely used in hydro-systems modeling as robust prediction tools that combine multiple decision trees. In this study, three newly developed ensemble machine learning models, namely gradient boost regression (GBR), AdaBoost regression (ABR) and random forest regression (RFR) are proposed for prediction of suspended sediment load (SSL), and their prediction performance and related uncertainty are assessed. The SSL of the Mississippi River, which is one of the major world rivers and is significantly affected by sedimentation, is predicted based on daily values of river discharge (Q) and suspended sediment concentration (SSC). Based on performance metrics and visualization, the RFR model shows a slight lead in prediction performance. The uncertainty analysis also indicates that the input variable combination has more impact on the obtained predictions than the model structure selection.  相似文献   

Formal proposal for the Bathonian GSSP (Middle Jurassic) in the Ravin du Bès Section (Bas-Auran, SE France)     

Sixto R. Fernández-López  Giulio Pavia  Elisabetta Erba  Myett Guiomar  Maria H. Henriques  Roberto Lanza  Charles Mangold  Davide Olivero  Daniele Tiraboschi 《Swiss Journal of Geoscience》2009,102(2):271-295

The Bathonian Global Stratotype Section and Point (GSSP) is proposed at the base of limestone bed RB071 (bed 23 in Sturani 1967) in the Ravin du Bès Section (43° 57′ 38′′ N, 6° 18′ 55′′ E), Bas-Auran area, “Alpes de Haute Provence” French department. The Ravin du Bès Section, as formal candidate GSSP for the base of the Bathonian Stage, satisfies most of the requirements recommended by the International Commission on Stratigraphy: 1) The exposure extends over 13 m in thickness. At the Bajocian-Bathonian transition, no vertical (bio-, ichno- or tapho-) facies changes, condensation, stratigraphic gaps or hiatuses have been recorded. Structural complexity, synsedimentary and tectonic disturbances, or important alterations by metamorphism are not relevant constraints. 2) There is a well-preserved, abundant and diverse fossil record across the boundary interval, with key markers (ammonites and nannofossils) for worldwide correlation. The base of the Bathonian Stage and Zigzag Zone in Bas-Auran corresponds to the first occurrence level of Gonolkites convergens Buckman, which coincides with the first occurrence of Morphoceras parvum Wetzel. Calcareous nannofossils, as secondary global marker, are present in all beds and allow characterizing the Bajocian-Bathonian transition. 3) Regional analyses of sequence stratigraphy and manganese chemostratigraphy are available. Spectral gamma-ray data corroborate an Early Bathonian deepening half-cycle of second order. 4) The criteria of accessibility, conservation and protection are assured by the “Réserve Naturelle Géologique de Haute Provence”. The Cabo Mondego Section (Portugal) is suggested as the Bathonian auxiliary section and point (ASSP) within this GSSP proposal.  相似文献   

Soil water dynamics at a midlatitude test site: Field measurements and box modeling approaches     

Mara Baudena  Ivan Bevilacqua  Davide Canone  Stefano Ferraris  Maurizio Previati  Antonello Provenzale 《Journal of Hydrology》2012

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Catchment-scale storm velocity: quantification,scale dependence and effect on flood response     

Efthymios I. Nikolopoulos  Marco Borga  Davide Zoccatelli  Emmanouil N. Anagnostou 《水文科学杂志》2014,59(7):1363-1376

Abstract

The concept of “catchment-scale storm velocity” quantifies the rate of storm motion up and down the basin accounting for the interaction between the rainfall space–time variability and the structure of the drainage network. It provides an assessment of the impact of storm motion on flood shape. We evaluate the catchment-scale storm velocity for the 29 August 2003 extreme storm that occurred on the 700 km²-wide Fella River basin in the eastern Italian Alps. The storm was characterized by the high rate of motion of convective cells across the basin. Analysis is carried out for a set of basins that range in area from 8 to 623 km² to: (a) determine velocity magnitudes for different sub-basins; (b) examine the relationship of velocity with basin scale and (c) assess the impact of storm motion on simulated flood response. Two spatially distributed hydrological models of varying degree of complexity in the representation of the runoff generation processes are used to evaluate the effects of the storm velocity on flood modelling and investigate model dependencies of the results. It is shown that catchment-scale storm velocity has a non-linear dependence on basin scale and generally exhibits rather moderate values, in spite of the strong kinematic characteristics of individual storm elements. Consistently with these observations and for both models, hydrological simulations show that storm motion has an almost negligible effect on the flood response modelling.

Editor Z.W. Kundzewicz; Guest editor R.J. Moore

Citation Nikolopoulos, E.I., Borga, M., Zoccatelli, D., and Anagnostou, E.N., 2014. Catchment-scale storm velocity: quantification, scale dependence and effect on flood response. Hydrological Sciences Journal, 59 (7), 1363–1376. http://dx.doi.org/10.1080/02626667.2014.923889  相似文献   

Soil C and N response to changes in winter precipitation in a subalpine forest ecosystem,NW Italy   总被引：1，自引：0，他引：1       下载免费PDF全文

Davide Viglietti  Michele Freppaz  Gianluca Filippa  Ermanno Zanini 《水文研究》2014,28(21):5309-5321

Among the potential effects of climate change on subalpine forest ecosystems during the winter season, the shift in snowline towards higher altitudes and the increase in frequency of rain events on the snowpack are of particular interest. Here, we present the results of a 2‐year field experiment conducted in a forest stand (Larix decidua) in NW Italy at 2020 m a.s.l. From 2009 to 2011, we monitored soil physical characteristics (temperature and moisture), and soil and soil solution chemistry, in particular carbon (C) and nitrogen (N) forms and their change in time, as affected by simulated late snowpack accumulation and rain on snow events. Late snowpack accumulation determined a stronger effect on soil thermal and moisture regimes than rain on snow events. Also soil chemistry was significantly affected by late snowfall simulation. Although microbial biomass C and N were not reduced by soil freezing, soil contents of the more labile dissolved organic carbon and inorganic N increased when the soil was affected by mild/hard freezing. Variations in the soil solution were shifted with respect to those observed in soil, with an increase in N‐NO₃^? concentrations occurring during spring and summer. This study highlights the potential N loss in subalpine soils under changing environmental conditions driven by a changing climate. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Cretaceous to Neogene structural evolution of the Lampedusa Shelf (Pelagian Sea, Central Mediterranean)     

Luigi Torelli  Mario Grasso  Glauco Mazzoldi  Davide Peis  Davide Gori 《地学学报》1995,7(2):200-212

Studies of multichannel seismic reflection profiles, calibrated with borehole data, have been carried out in the Tunisian shelf surrounding the islands of Lampione and Lampedusa, in order to define the Mesozoic-Cenozoic stratigraphie and structural evolution of this sector of the Pelagian foreland. The stratigraphy and subsidence history show a subsiding Upper Jurassic carbonate platform buried, by syn- and post-rift neritic to deep marine siliciclastics, marls and limestones of Neocomian-early Eocene age. Thick Middle-Upper Eocene shallow-water carbonates (Halk el Menzel Fm.), lie unconformably over the deep-water sediments and exhibit progradational geometries.
Messinian evaporites are confined to the deepest parts of the Neogene basins and Plio-Quaternary sediments are widespread over the area. Several unconformities affect the stratigraphic column and have been interpreted as related to compressive events during Late Cretaceous-early Tertiary times. These compressive events produced uplift, folding and reverse faulting, trending about NW-SE and partly reactivating Lower Cretaceous extensional structures. The uppermost regional unconformity indicates widespread emergence and erosion during Oligocene and Miocene tintes and was probably related to a younger compressional phase. A strong Upper Miocene-Quaternary extension event also affected the area, characterized by WNW-ESE trending normal faults, parallel to faults flanking the main grabens of the Sicily Strait rift zone. Since the Messinian, the structural evolution of the area has been controlled by rift-related processes which triggered crustal extension in the Pelagian foreland.  相似文献   

Experimental and Numerical Studies on the Seismic Response of R.C. Hollow Bridge Piers   总被引：3，自引：2，他引：1  

Gian?Michele?CalviEmail author  Alberto?Pavese  Alessandro?Rasulo  Davide?Bolognini 《Bulletin of Earthquake Engineering》2005,3(3):267-297

Appropriate seismic assessment of reinforced concrete bridges is an important challenge in structural engineering in consideration of the number and relevance of bridges built without applying advanced codes of practice and of the strategic role of transportation networks in modern economy. This paper focuses on some relevant aspects of the damage development and collapse modes of hollow piers, as commonly designed in the past. The following aspects have been considered: absence of confinement, inadequate shear strength, shifting of the critical section, insufficient length of lap splices. A series of experimental tests has been designed and performed; the capacity of predicting appropriate results of formulations recommended in codes of practice or proposed in recent research documents has been checked comparing experimental and analytical results.  相似文献   

Minor changes in surface-water fertility across the oceanic anoxic event 1d (latest Albian,SE France) evidenced by calcareous nannofossils     

Fabienne?GiraudEmail author  Davide?Olivero  Fran?ois?Baudin  Stéphane?Reboulet  Bernard?Pittet  Olivier?Proux 《International Journal of Earth Sciences》2003,92(2):267-284

The latest Albian sediments deposited in the Vocontian basin in south-eastern France record the oceanic anoxic event (OAE) 1d, locally named the Breistroffer interval. They are represented by argillaceous marls and marls, containing organic matter (total organic carbon varying from 0.8 to 1%). Changes in calcareous nannofossil abundance and assemblage composition as well as macrofauna abundance, ichnofossil assemblage, and bioturbation intensity were analysed in order to evaluate the main palaeoenvironmental factors controlling the deposition of the OAE 1d sediments in this area. The pelagic carbonate production is limited and the carbonate fraction is predominantly of nektonic/benthic, and of allochthonous origin from carbonate platforms. The enrichment in organic carbon within the Breistroffer interval is weak and not associated with high surface-water productivity. The organic matter is mainly terrigenous. Its record is due to (1) a good preservation under dysoxic conditions within the sediments, and (2) a weak input of allochthonous carbonates. Eustatic fluctuations strongly influenced the variations of nannofossil and macrofauna abundances. Distinctive patterns in nannofossil assemblages and macrofauna abundances within the Breistroffer interval are also recognized, reflecting changes from mesotrophic to more oligotrophic conditions which are probably controlled by climate.  相似文献