Dynamics of sea-surface temperature anomalies in the Southern Ocean diagnosed from a 2D mixed-layer model     

Frédéric Vivier  Daniele Iudicone  Fabiano Busdraghi  Young-Hyang Park 《Climate Dynamics》2010,34(2-3):153-184

We analyze the processes responsible for the generation and evolution of sea-surface temperature anomalies observed in the Southern Ocean during a decade based on a 2D diagnostic mixed-layer model in which geostrophic advection is prescribed from altimetry. Anomalous air–sea heat flux is the dominant term of the heat budget over most of the domain, while anomalous Ekman heat fluxes account for 20–40% of the variance in the latitude band 40°?60°S. In the ACC pathway, lateral fluxes of heat associated with anomalous geostrophic currents are a major contributor, dominating downstream of several topographic features, reflecting the influence of eddies and frontal migrations. A significant fraction of the variability of large-scale SST anomalies is correlated with either ENSO or the SAM, each mode contributing roughly equally. The relation between the heat budget terms and these climate modes is investigated, showing in particular that anomalous Ekman and air–sea heat fluxes have a co-operating effect (with regional exceptions), hence the large SST response associated with each mode. It is further shown that ENSO- or SAM-locked anomalous geostrophic currents generate substantial heat fluxes in all three basins with magnitude comparable with that of atmospheric forcings for ENSO, and smaller for the SAM except for limited areas. ENSO-locked forcings generate SST anomalies along the ACC pathway, and advection by mean flows is found to be a non-negligible contribution to the heat budget, exhibiting a wavenumber two zonal structure, characteristic of the Antarctic Circumpolar Wave. By contrast SAM-related forcings are predominantly zonally uniform along the ACC, hence smaller zonal SST gradients and a lesser role of mean advection, except in the SouthWest Atlantic. While modeled SST anomalies are significantly correlated with observations over most of the Southern Ocean, the analysis of the data-model discrepancies suggests that vertical ocean physics may play a significant role in the nonseasonal heat budget, especially in some key regions for mode water formation.  相似文献   

Earth–Moon Weak Stability Boundaries in the restricted three and four body problem     

Daniele Romagnoli  Christian Circi 《Celestial Mechanics and Dynamical Astronomy》2009,103(1):79-103

This work deals with the structure of the lunar Weak Stability Boundaries (WSB) in the framework of the restricted three and four body problem. Geometry and properties of the escape trajectories have been studied by changing the spacecraft orbital parameters around the Moon. Results obtained using the algorithm definition of the WSB have been compared with an analytical approximation based on the value of the Jacobi constant. Planar and three-dimensional cases have been studied in both three and four body models and the effects on the WSB structure, due to the presence of the gravitational force of the Sun and the Moon orbital eccentricity, have been investigated. The study of the dynamical evolution of the spacecraft after lunar capture allowed us to find regions of the WSB corresponding to stable and safe orbits, that is orbits that will not impact onto lunar surface after capture. By using a bicircular four body model, then, it has been possible to study low-energy transfer trajectories and results are given in terms of eccentricity, pericenter altitude and inclination of the capture orbit. Equatorial and polar capture orbits have been compared and differences in terms of energy between these two kinds of orbits are shown. Finally, the knowledge of the WSB geometry permitted us to modify the design of the low-energy capture trajectories in order to reach stable capture, which allows orbit circularization using low-thrust propulsion systems.  相似文献   

Detecting multi-scale riverine topographic variability and its influence on Chinook salmon habitat selection     

Jenna Duffin  Richard A. Carmichael  Elowyn M. Yager  Rohan Benjankar  Daniele Tonina 《地球表面变化过程与地形》2021,46(5):1026-1040

Quantifying geomorphic conditions that impact riverine ecosystems is critical in river management due to degraded riverine habitat, changing flow and thermal conditions, and increasing anthropogenic pressure. Geomorphic complexity at different scales directly impacts habitat heterogeneity and affects aquatic biodiversity resilience. Here we showed that the combination of continuous spatial survey at high resolution, topobathymetric light detection and ranging (LiDAR), and continuous wavelet analysis can help identify and characterize that complexity. We used a continuous wavelet analysis on 1-m resolution topobathymetry in three rivers in the Salmon River Basin, Idaho (USA), to identify different scales of topographic variability and the potential effects of this variability on salmonid redd site selection. On each river, wavelet scales characterized the topographic variability by portraying repeating patterns in the longitudinal profile. We found three major representative spatial wavelet scales of topographic variability in each river: a small wavelet scale associated with local morphology such as pools and riffles, a mid-wavelet scale that identified larger channel unit features, and a large wavelet scale related to valley-scale controls. The small wavelet scale was used to identify pools and riffles along the entire lengths of each river as well as areas with differing riffle-pool development. Areas along the rivers with high local topographic variability (high wavelet power) at all wavelet scales contained the largest features (i.e., deepest or longest pools) in the systems. By comparing the wavelet power for each wavelet scale to Chinook salmon redd locations, we found that higher small-scale wavelet power, which is related to pool-riffle topography, is important for redd site selection. The continuous wavelet methodology objectively identified scales of topographic variability present in these rivers, performed efficient channel-unit identification, and provided geomorphic assessment without laborious field surveys.  相似文献   

Biosedimentary record of postglacial coastal dynamics: high‐resolution sequence stratigraphy from the northern Tuscan coast (Italy)     

Alessandro Amorosi  Veronica Rossi  Daniele Scarponi  Stefano Claudio Vaiani  Anupam Ghosh 《Boreas: An International Journal of Quaternary Research》2014,43(4):939-954

Integrating analysis of the benthic palaeoecological record with multivariate ordination techniques represents a powerful synergy able to provide an improved characterization of coastal depositional facies in a sequence stratigraphical perspective. Through quantitative analysis of benthic foraminifer, ostracod and mollusc associations from the postglacial succession of Core M3 (Arno coastal plain, Tuscany, Italy), and application of detrended correspondence analysis (DCA) to the mollusc sub‐data set, we offer a refined picture of stratigraphical variations in faunal content from a paralic depositional setting, and reconstruct the palaeoenvironmental gradients that account for such variations. Despite distinct ecological behaviours, and taphonomic and sedimentological constraints, a strong ecological control on meio‐ and macrofaunal biofacies and taxa turnover is documented across the study succession. Amongst all possible mechanisms that may play a role in ‘shaping’ fossil distribution, the ecological signal driven by salinity represents the most prominent factor controlling the composition of fossil associations in the cored succession. Molluscs can even provide outstanding quantitative estimates of palaeosalinity along the sampled core. When plotted stratigraphically, the three fossil sub‐data sets show consistent patterns of vertical evolution that enable prompt identification of the key surfaces for sequence stratigraphical interpretation in otherwise lithologically indistinguishable deposits. The concomitant maximum richness of species with strong marine affinity, paralleled by the highest DCA salinity estimates, allows recognition of the maximum flooding zone, dated to ～7.7 cal. ka BP, within a homogeneous succession of outer lagoon clays. These clays are sandwiched between early transgressive, swamp to inner lagoon deposits and overlying prograding coastal?alluvial plain facies.  相似文献   

Gully head modelling: A Mediterranean badland case study          下载免费PDF全文

Dino Torri  Jean Poesen  Mauro Rossi  Valerio Amici  Daniele Spennacchi  Cati Cremer 《地球表面变化过程与地形》2018,43(12):2547-2561

Predicting the location of gully heads in various environments is an important step towards predicting gully erosion rates. So far, field data collection and modelling of topographic thresholds for gully head development has mainly focused on gullies that formed in forested areas, rangelands, pastures and cropland. Such information for gullies in badlands however is very scarce. Therefore, this paper aims to extend the database on gully head topographical thresholds through data collection in a badland area and to improve the prediction of gully heads forming at sites with a very low erosion resistance value. For this, we chose a badland site located in central Italy that is characterized by biancana forms and both active and dormant gullies. The definition of the conditions under which present‐day gully heads developed allowed a better modelling of the gully head threshold equation, with modification of a previous model and the exemplification of how to use the updated model. The model shows that the resistance to gully head retreat depends on slope gradient and drainage area at gully heads, land use at the moment of gully development (as numerically expressed using parameters derived from the Runoff Curve Number method), surface rock fragment cover, presence of joints, pipes, and factors/processes affecting detachment rate. This study attempted to better understand environmental conditions that control the development of gully heads in badlands through a combination of field data collection of gully heads, an analysis of land use changes over 10 centuries, focusing on the period 1820–2005, and land use management through repeat photography and a critical examination of historical documents. © 2018 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

Operation of two major reservoirs of Iran under IPCC scenarios during the XXI century          下载免费PDF全文

Habib Akbari‐Alashti  Andrea Soncini  Yagob Dinpashoh  Ahmad Fakheri‐Fard  Siamak Talatahari  Daniele Bocchiola 《水文研究》2018,32(21):3254-3271

We assess the effects of prospective climate change until 2100 on water management of two major reservoirs of Iran, namely, Dez (3.34 × 10⁹ m³) and Alavian (6 × 10⁷ m³). We tune the Poly‐Hydro model suited for simulation of hydrological cycle in high altitude snow‐fed catchments. We assess optimal operation rules (ORs) for the reservoirs using three algorithms under dynamic and static operation and linear and non‐linear decision rules during control run (1990–2010 for Dez and 2000–2010 for Alavian). We use projected climate scenarios (plus statistical downscaling) from three general circulation models, EC‐Earth, CCSM4, and ECHAM6, and three emission scenarios, or representative concentration pathways (RCPs), RCP2.6, RCP4.5, and RCP8.5, for a grand total of nine scenarios, to mimic evolution of the hydrological cycle under future climate until 2100. We subsequently test the ORs under the future hydrological scenarios (at half century and end of century) and the need for reoptimization. Poly‐Hydro model when benchmarked against historical data well mimics the hydrological budget of both catchments, including the main processes of evapotranspiration and streamflows. Teaching–learning‐based optimization delivers the best performance in both reservoirs according to objective scores and is used for future operation. Our projections in Dez catchment depict decreased precipitation along the XXI century, with ?1% on average (of the nine scenarios) at half century and ?6% at the end of century, with changes in streamflows on average ?7% yearly and ?13% yearly, respectively. In Alavian, precipitation would decrease by ?10% on average at half century and ?13% at the end of century, with streamflows ?14% yearly and ?18% yearly, respectively. Under the projected future hydrology, reservoirs' operation would provide lower performance (i.e., larger lack of water) than now, especially for Alavian dam. Our results provide evidence of potentially decreasing water availability and less effective water management in water stressed areas like Northern Iran here during this century.  相似文献   

Using the applied element method for modelling calcium silicate brick masonry subjected to in‐plane cyclic loading          下载免费PDF全文

Daniele Malomo  Rui Pinho  Andrea Penna 《地震工程与结构动力学》2018,47(7):1610-1630

The response of calcium silicate unreinforced masonry construction to horizontal cyclic loading has recently become the focus of experimental and numerical research, given its extensive use in some areas of the world that are now exposed to induced earthquakes (eg, north of the Netherlands). To assess the seismic behaviour of such construction, a relatively wide range of modelling methodologies are available, amongst which the discrete elements approach, which takes into account the intrinsic heterogeneity of a brick‐mortar assembly, can probably be deemed as the most appropriate computational procedure. On the other hand, however, since discrete elements numerical methods are based on a discontinuum domain, often they are not able to model every stage of the structural response adequately, and because of the high computational burden required, the analysis scale should be chosen carefully. The applied element method is a relatively recent addition to the discrete elements family, with a high potential for overcoming the aforementioned limitations or difficulties. Initially conceived to model blast events and concrete structures, its use in the earthquake engineering field is, of late, increasing noticeably. In this paper, the use of the applied element method to model the in‐plane cyclic response of calcium silicate masonry walls is discussed and scrutinised, also through the comparison with experimental results of in‐plane cyclic shear‐compression tests on unreinforced masonry walls.  相似文献   

Estimating free parameters in 2D inversion: example of gravity inversion in a rifted basement     

João B.C. Silva  Darcicléa F. Santos  Daniele P. Monteiro 《Geophysical Prospecting》2020,68(3):1057-1071

We advance a principle directed to assigning numerical values to free parameters usually present in inversion methods. It may be formulated as: ‘Optimum estimates of free parameters in an inversion procedure must lead, in tests using synthetic data, to solutions whose geometrical expression reflects the main qualitative or semiquantitative geological characteristic of the study area.’ To this end, the interpreter should (i) specify a typical anomalous source geometry which incorporates the most relevant geological information for the study area, (ii) compute the corresponding gravity anomaly and (iii) invert the anomaly for the source geometry finding the numerical values of the free parameters that lead to a solution closest to the typical source. Application of the above methodology to synthetic and real data from the basement relief of a rift basin has asserted its efficacy.  相似文献   

Ambient vibration tools to validate the rigid diaphragm assumption in the seismic assessment of buildings     

Daniele Sivori  Marco Lepidi  Serena Cattari 《地震工程与结构动力学》2020,49(2):194-211

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Formation of an ‘a’ā lava delta: insights from time-lapse multibeam bathymetry and direct observations during the Stromboli 2007 eruption     

Alessandro Bosman  Daniele Casalbore  Claudia Romagnoli  Francesco Latino Chiocci 《Bulletin of Volcanology》2014,76(7):1-12

Five consecutive multibeam bathymetries collected before, during, and after the 2007 Stromboli eruption, combined with visual inspections, allowed us to document the morphological evolution of an ‘a’ā lava-fed delta and to reconstruct the main processes acting during its submarine emplacement. The 2007 Stromboli delta extended down to 600-m water depth and covered an area of 420?×?10³ m², with a maximum thickness of 65 m and a total estimated volume of ≈7?×?10⁶ m³, i.e., three times larger than its subaerial counterpart. The lava delta grew mainly through the emplacement of discrete lobes about 50–150 m in size. Lobes were fed from point sources along the paleoshoreline, and their subaqueous pathways seem to be mainly controlled by the submarine morphology, with flows mostly filling in depressions left by previous lobes. The main controlling factors on the lobe morphology and thickness are the effusion rates and the pre-eruption morphology, i.e., the geometry and gradients of the basal surface. Data also shows that sudden slope failure of portions of the submarine delta may occur simultaneously with accretion, implying that a significant part of the delta material can be transported to greater depths by submarine gravity flows. The present study is relevant for future monitoring and hazard assessment during the growth of active lava-fed deltas as well as for a better interpretation of ancient volcaniclastic successions inland.  相似文献