1,721,066 research outputs found
Dynamic behaviour of lagoon ecosystems
Full text linkAn analysis of coastal lagoon ecosystem dynamics is proposed the aim is to achieve a better understanding of mechanisms responsible of vegetal species substitution and water anoxia phenomena occurring in lagoons as a consequence of eutrophication such a understanding is fundamental to individuate more effective management strategies for the control of eutrophication processes.
The analysis is carried out by using a eutrophication model which allows the simulation of the temporal evolution of the concentration in the water column and into sediments of the significant species affecting eutrophication phenomena.
The dynamic behaviour of the lagoon ecosystem state, for an assigned parameter space, is analysed by simulations carried out varying both the phosphorous external load and the maximum tidal flow rate at the inlet connecting the lagoon to the sea , which were assumed as control parameters.
The response diagram, obtained by simulations, varying the value of control parameters, shows the existence of different ranges of stability of the ecosystem, characterized by the dominance of a specific group of primary producers and by a different ecosystem vulnerability to summer water anoxia. A catastrophic bifurcation, which manifests as an abrupt change of the dominant species from eelgrass to macro algae, occurs for some critical values of the control parameters
Italian Academy Colombia Fellowship
No full textDuring the fall semester spent at the Italian Academy , cosponsored by the Earth and Environmental Engineering Department of Columbia University of New York, I worked on the research project ‘ Climate changes from decade to century: flood/drought dynamics’.
Such a research project involves different partners and Institutions , namely Columbia University (USA) , University of Rome ‘ La Sapienza’(Italy) , National Research Center (CNR-Italy), Institute of Numerical Model (Russian Science Academy), University of Tuscia Italy).
The research goal is to produce scientifically sound scenarios of flood and drought risk in N. America and Europe and their projected changes under IPCC scenarios.
A novel integrated modelling approach is used to address this issue. The approach entails integration of analyses from a low order dynamical systems model, a medium resolution current ocean-atmosphere GCM, and statistical tools for connecting atmospheric moisture transport and extreme precipitation incidence to the underlying low frequency climate state.
A low order model explores the interactions of the key natural modes of ocean-atmosphere variability and their interaction with the mid-latitude atmosphere.
The CGM model INMCM3.0 (Volodin & Diansky 2006) allows to simulate planetary climatic conditions for long periods of time under current conditions and under enhanced greenhouse gases conditions. However, given its complexity only a limited number of ensemble runs can typically be performed for a fixed set of parameters. Thus, its use is complementary to the low order models where substantial exploration of the parameters and the associated regimes can be done.
In the Fall semester spent in the Italian Academy the research has been addressed to study:
- the organization and evolution of climate extremes in the mid-latitude as they are influenced by low-frequency climate modes associated with ocean-atmosphere interactions; specifically such influences have been explored by using observations and low-order models.
- precipitation extremes simulated by the medium resolution GCM ( INMCM3.0) as are analyzed for the Mediterranean region.
The main findings of the study are extensively discussed in the paper ‘Surface Temperature Gradient and their relation to Mid-latitude Circulation Dynamics & Interannual Precipitation variability: Trends and links to Enso in Observations and Low-order Climate Models ’ by C. Karamperidou, F. Cioffi & U. Lall, and in the two presentations at the AGU2010 Fall Conference , namely (a) ‘"Northern Hemisphere Meridional and Zonal Temperature Gradients and their Relation to Hydrologic Extremes at Mid-latitudes: Trends, Variability and Link to Climate Modes in Observations and Simulations" , by C. Karamperidou, U. Lall & F. Cioffi ; (b) GCM Projections of Precipitation Extremes in the Mediterranean: Changes and Low frequency Characteristics by F. Cioffi ; U. Lall , E. Volodin , C. Karamperidou , R. Purini .
These findings are summarized in the following. The analysis of rainfall patterns under global warming shows an increase of rainfall extremes in both frequency and intensity in northern Europe and a decrease in most of the Mediterranean. In the latter region an increase of dry conditions is also observed. The change in the rainfall patterns can be explained by a northward shift of the North Atlantic winter storm track that is one of the main factors in determining moisture and heat transport associated with extreme hydrological events. It depends on how the jet stream dynamics are modulated by large scale ocean-land boundary conditions which depend in turn on both the state of evolution of the known inter-annual and multi-decadal natural variability ( e.g. El Nino-Southern Oscillation (ENSO) and the North Atlantic Oscillation (NAO)) and on changes in meridional and zonal surface temperature gradients ( Equator- Pole gradient (EPG) and Ocean-Land contrast ( OLC), respectively). From the 20th century observations is emerged that different combinations of EPG and OLC are associated with precipitation anomalies at mid-latitudes as Mediterranean and European regions. The Northward shift of the North Atlantic storm track and the associated rainfall patterns are related to a reduction of both EPG and OLC as a consequence of anthropogenic forcing
visiting scholar
No full textWe explore the evolution of mid-latitude circulation anomalies as a potential surrogate
for changes in advection of moisture and heat using a sequence of progressively complex low order
models. The Lorenz (1984) model is considered for mid-latitude circulation; it is then coupled to a Stommel
Box model representing the Atlantic thermohaline circulation; and then these models are linked to a low
order El Niño-Southern Oscillation (ENSO) model. The interaction between the Pacific ENSO model and
the Atlantic (Stommel) model is also modeled. The integrated representations provide different levels of
temporal interactions of tropical and mid-latitude circulation. The coupled models are used to assess how
the probability distribution and temporal structure (low frequency variability) of circulation extremes evolves
in such simple models, as the degree of interaction across these identified climate modes is introduced and
varied. Model parameters are selected to conform approximately to the properties exhibited by the data
observed over the 20th century. We note the intermittence and regime like behavior in the solution space
as the purely atmospheric model (Lorenz '84) receives low frequency information from the other models.
While moist circulation is not explicitly modeled, the results from the model(s) can be interpreted in terms of
the potential changes in the key modes of eddy transport of moisture and heat. Parametric analyses of the
effects as a function of the degree of coupling across the models are presented
Analisi sperimentale dei processi di sedimentazione:dottorato di ricerca in ingegneria sanitaria
No full textAssociate Visiting Professor
No full textDuring the stay in Columbia University it has been carried out an investigation on the future patterns of daily temperature, precipitation and sea level in different coastal regions , under global warming scenario simulated by CGMs, in order to provide the input data for performing hydrodynamics/morphodynamics analysis of surface and groundwater flows in such regions. The research is address to the development and application of statistical downscaling approaches, as Hidden Markov Model and Non-homogeneous Hidden Markov model, Artificial Neural Network and combined approaches; these approaches are applied to a number of regions as South Florida, Tanzania and Piana Pontina. Further it has been developped a statistical forecast model for Tropical Cyclone Rainfall and flood events for the Hudson River, New York City area. Specifically the aim is the construction of a system of statistical models able to translates the attributes of a tropical cyclone to rainfall intensity at selected stations within the watershed of Hudson River and to transforms, , the rainfall intensities, calculated for the ensemble of the stations, to the streamflows at specific points of the tributaries of the Hudson River, to use as inputs in a hydrodynamic model that includes storm surge dynamics for the simulation of coastal flooding along the Hudson River.Luglio 201
Analisi dei profili di velocità e concentrazione di solidi in un canale rettangolare a fondo mobile
No full text
From rooted to floating vegetal species in lagoons as a consequence of the increases of external nutrient load: An analysis by model of the species selection mechanism
No full textIn this paper, the substitution mechanism of rooted aquatic plants (as eelgrass) with floating species (as Ulva r.) in lagoons are inquired by using a eutrophication model. The simulations carried out for the specific case of the Lagoon of Tortolì, in Sardinia (Italy), demonstrate the determinant role played by the increase of external phosphorous loads in the vegetal species selection and offer a possible explanation of the selection mechanism. Once the maximum accumulation capability of adsorbed phosphorous in sediments is reached, the rate of external phosphorous loads produces an increment in the dissolved phosphorous in the water column; such an increment favours the growth of floating species which inhibit, mainly due to light competition effect, the growth of rooted plants. In the paper, the serious consequences of such a selection in terms of eutrophication processes and vulnerability of anoxic crises are emphasised. © 2005 Elsevier Inc. All rights reserved
A two-dimensional self-adaptive hydrodynamic scheme for the assessment of the effects of structures on flooding phenomena in river basins
No full textIn order to assess the effects of river and floodplain engineering projects on flooding, a new self-adaptive hydrodynamic scheme for the simulation of two-dimensional river flows is proposed. The depth-averaged motion equations are solved numerically using a fractional step method, in which the convective terms are calculated using the inverse characteristics method and the remaining terms with an explicit method based on a finite difference method. The integration is performed on a dynamically self-adaptive calculus grid, which allows representation of the movable boundary between wetting and drying regions of the basins to follow the effective developments in time and space, of the expansion phenomenon of flood. The proposed procedure allows the grid's dynamic refinement to avoid coordinate transformation or the use of unstructured grids. The proposed method is simple and allows the thickening of the grid to accommodate the flooding phenomena on the floodplain and to calculate the velocity in the domain regions in which a higher space resolution is required. Therefore, flows running through structures such as weirs, gates, bridges or culverts can be simulated. In the paper two different-case studies, approached with the proposed self-adaptive calculation scheme, are discussed. The studies concern the analysis of the effects of structures, such as roads or embankments, on flooding phenomena in the Tiber and Tanaro basins respectively. Copyright (C) 2003 John Wiley Sons, Ltd
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