Search

On the morning of September 26, 2007, a heavy precipitation event (HPE) affected the Venice lagoon and the neighbouring coastal zone of the Adriatic Sea, with 6-h accumulated rainfall summing up to about 360 mm in the area between the Venetian mainland, Padua and Chioggia. The event was triggered and maintained by the uplift over a convergence line between northeasterly flow from the Alps and southeasterly winds from the Adriatic Sea. Hindcast modelling experiments, using standalone atmospheric models, failed to capture the spatial distribution, maximum intensity and timing of the HPE. Here we analyze the event by means of an atmosphere-wave-ocean coupled numerical approach. The combined use of convection permitting models with grid spacing of 1 km, high-resolution sea surface temperature (SST) fields, and the consistent treatment of marine boundary layer fluxes in all the numerical model components are crucial to provide a realistic simulation of the event. Inaccurate representations of the SST affect the wind magnitude and, through this, the intensity, location and time evolution of the convergence zone, thus affecting the HPE prediction. [ABSTRACT FROM AUTHOR]

In this work we assess the quality of the wind fields provided over the Adriatic Sea by the Regional Climate Model COSMO-CLM with reference to a control (CTR) period from 1971 to 2000 and to a future period from 2071 to 2100 under IPCC RCP 8.5 scenario (SCE), focusing on the implications for wave climate characterisation. Model skills have been assessed by comparing CTR results in terms of gross statistical properties and storm features against wind data from coastal observatories along the whole Italian Adriatic coast, showing a satisfactory capability of capturing the main features of mean observed seasonal variability. Significant achievements with reference to existing climatological models have been observed especially in terms of wind directionality, with unprecedented performances in reproducing the bimodal dominance of Bora (from northeast) and Sirocco (from southeast) in the northern basin, and the typical patterns of Bora jets flowing from the mountain ridges enclosing the Adriatic Sea on its eastern side. Future projections generally confirm the tendency to a decreasing energy trend envisaged by previous studies, with a more marked effect for extreme events in the northern basin. Based on the comparison between climatological wind fields and the results of a SWAN wave model run forced by COSMO-CLM, we also define and test a criterion for a rapid identification of some relevant case studies for dedicated wave modelling experiments, without the need of running entire climatological wave simulations. This permits to focus the analysis of climatological oceanographic extreme events to a limited number of selected cases, allowing remarkable saving of computational effort especially if an ensemble approach is desired [ABSTRACT FROM AUTHOR]

The northern Adriatic Sea is a basin where dense shelf waters form during winters if the following favorable conditions are attained: high salinities, mainly related to low river water discharge (Po river in primis) during fall season, and strong heat fluxes induced by cold and dry Bora wind events blowing from north-east. Extremely favorable conditions to Northern Adriatic Dense Waters (NAdDW) formation characterized winter 2012 when, following several months of low Po river runoff, a strong event of Cold Air Outbreak (CAO) occurred from the end of January until mid-February. Consequently, the mean temperature of northern Adriatic waters dropped to about 6°C and exceptional densities (potential density anomaly locally exceeding 30.0 kg m − 3 ) were reached. The production and spreading mechanisms of dense water in the Adriatic Sea have been modeled by means of the COAWST (Coupled-Ocean–Atmosphere-Wave-Sediment-Transport) modeling system. The model builds upon a high-resolution (1 km spaced horizontal grid), fully 3-D primitive equations hydrodynamic model coupled with a phase-averaged wave model and sediment routines, and is driven by simulated atmospheric forcings. The dataset used to assess model outputs relies on the measurements acquired during the dedicated field campaigns “Operation Dense Water”, a set of two rapid response cruises carried out in southern Adriatic during winter 2012, and by five mooring arrays deployed in the Southern Adriatic Margin (SAM) that allowed the continuous acquisition of temperature, salinity, currents and suspended matter samples. Results from the integrated data-model approach suggest that the NAdDW propagates along the shelf to the southern basin following both a shallower vein and a deeper stream, with a process characterized by a strong variability (mean value of 0.31 Sv with peaks rapidly growing in the first weeks after the CAO up to 2.19 Sv). Additionally, COAWST capability to couple different numerical models allowed to disentangle the relative importance of aspects on dense water generation, mixing and spreading, demonstrating how coupled runs can lead to volumes up to 50% larger with respect to uncoupled simulations. Additional light is shed on the transport pathways off the shelf and on possible sediment transport phenomena in the area, in this benefiting from an unprecedented spatial resolution and a new bathymetry reflecting very high resolution data acquired via multi-beam techniques. Although dense water propagation appears as a relatively large-scale process involving the whole western side of the SAM, topographic local discontinuities and seabed slopes appear crucial in triggering descent and governing flow patterns. The presence of suspended sediment along the water column, despite not significantly influencing the overall fluxes across sections, is responsible of pulling part of the veins towards deeper zones. [ABSTRACT FROM AUTHOR]

Sea surface temperature (SST) and turbidity (T) derived from Landsat-8 (L8) imagery were used to characterize river plumes in the Northern Adriatic Sea (NAS) during a significant flood event in November 2014. Sea surface salinity (SSS) from an operational coupled ocean-wave model supported the interpretation of the plumes interaction with the receiving waters and among them. There was a good agreement of the SSS, T, and SST fields at the sub-mesoscale and mesoscale delineation of the major river plumes. L8 30m resolution enabled also the description of smaller plume structures. Sharp fronts in T and SST delimited each single river plume. The isotherms and turbidity isolines coupling varied among the plumes due to differences in particle loads and surface temperatures in the discharged waters. The different plumes reflectance spectra were related to the lithological fingerprint of the sediments in the river catchments. [ABSTRACT FROM AUTHOR]

In this paper, we investigate the impact of climate change on coastal sediment transport in a deltaic system in the northern Adriatic Sea, with reference to the period 2070-2099 in the IPCC A1B emission scenario. Wind fields obtained by means of the high-resolution regional climate model Consortium for Small-scale Modelling-Climate Limited-area Modelling were employed for computing wave climate at basin scale by means of the spectral wave model Simulating Waves Nearshore. This was used as a constraint for a nearshore hydromorphodynamic model (MIKE LITPACK), which was applied to a test site on the Po River Delta, located in northern Italy. Relevant sediment transport processes have been studied at storm and decadal time scales in order to capture climate change effects on single events and as an overall trend. The transport rates in the A1B climate change scenario were then compared with the corresponding results of a control analysis (period 1965-1994) representing the actual climate. Although predicted wave climate in the investigated scenario displays an overall decrease in sea severity offshore in the northern Adriatic Sea, the effects of these modifications are modulated during the onshore propagation, with different impacts on sediment transport depending on the considered process and time scale. The strategy presented in this work can find fruitful applications in the long-term modelling of coastal and transitional environments, in which morphology is strongly influenced by sediment transport in the nearshore zone, suggesting a methodological approach for coastal planning and management. [ABSTRACT FROM AUTHOR]

Sclavo, M., Benetazzo, A., Carniel, S., Bergamasco, A., Falcieri, F.M., and Bonaldo, D., 2013. Wave-current interaction effect on sediment dispersal in a shallow semi-enclosed basin The shallow northern Adriatic Sea (namely Gulf of Venice) serves as a model for exploring the interaction of surface gravity waves and oceanic currents and how they influence bottom sediment dispersal and bathymetry evolution. This wave-current interaction effect is investigated using the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) modeling system. COAWST relies on the Regional Ocean Modeling System (ROMS), the Simulating WAves Nearshore (SWAN) model, and the CSTMS (Community Sediment Transport Modeling System) models and routines. The 2-way data transfer between wave and ocean circulation models is synchronous via MCT (Model Coupling Toolkit), with ROMS providing to SWAN the 2-D current field, free surface elevation, and bathymetry. COAWST modeling system is implemented on two computational grids at different horizontal resolution: a parent grid (with resolution of 2.0 km) covering the whole Adriatic Sea and a child grid resolving the Gulf of Venice at a resolution of 0.5 km. Simulated waves and currents are validated against in-situ observations at the CNR-ISMAR Acqua Alta oceanographic tower, located 15 km off the Venice lagoon. The analysis of wave-current interaction effect on sediment dispersal and sea bottom evolution are performed over the 2011 winter season (January-March) with particular focus on the waves generated by dominant and prevailing winds blowing on the Adriatic Sea: Bora and Sirocco. Results show that while the effects on bottom stress may vary depending on wave propagation and current direction, the effects on advective dynamics may become dominant particularly in presence of severe storms with parallel wave propagation and global circulation, which is the case of Bora storms in northern Adriatic Sea. [ABSTRACT FROM AUTHOR]

The paper describes formation and spreading of dense shelf waters in the Adriatic Sea (North Adriatic Dense Water, NAdDW) during the winter of 2012 as a consequence of an intense and long cold air outbreak of northeasterly Bora winds. As a result, during February 2012 northern Adriatic Sea water temperature dropped to about 6 °C and density exceeded 1030 kg/m 3 , most likely the maximum value since 1929. NAdDW dynamics has been investigated by means of a 3-D ocean-wave coupled model running on a high resolution and eddy-permitting grid. The numerical experiments have relied on the Coupled-Ocean–Atmosphere-Wave-Sediment-Transport (COAWST) system forced one-way with atmospheric forcings provided by the model COSMO-I7. A suite of observational data has been used to characterize the Bora event and evaluate numerical model performance. At sub-basin scales, the newly formed waters flowing southerly have produced a water renewal of the northern Adriatic, as more than 50% of water volumes have left the basin. Dense waters volume transports, evaluated through different Adriatic cross-sections, have been modulated by tides (damped for the densest water masses) and reached about 1 Sv. The contribution of wave-induced forcings has been quantified and examined, indicating that these represent a major driving mechanism during NAdDW production and spreading phases. This work provides evidence that NAdDW is spread accordingly with two different mechanisms: at early stages of its formation, the wind-driven ocean circulation pushes newly formed waters to leave the northern basin with relatively high speeds (about 0.30 m/s). Later on, remaining NAdDW leaks slowly out (0.09 m/s as average) from the production site. Residence times of dense waters in the north, middle, and south Adriatic Sea are also documented. [ABSTRACT FROM AUTHOR]

Abstract: This model is based on the concept of transport concentration, defined as the time-averaged concentration in a given location of a lagoon, which determines the long-term net transport of sediments as the sum of a dispersive and an advective flux. Dispersive net flux of sediments is due to the alternate components of the tidal flow, while the advective net flux of sediments is due to the residual (Eulerian) component of the tidal, fluvial and littoral flow and possibly to the asymmetry between flow and ebb tide. The long-term deposition (or erosion) rate in a given location is expressed as proportional to the difference between the local transport concentration and the local equilibrium concentration, depending in turn on the local stirring action by waves and currents. The two-dimensional model is able to reproduce the ontogeny of a tidal lagoon as a consequence of a breaching of the littoral dune line. During the ontogenetic phase, the system tends rapidly toward a quasi-equilibrium condition apparently characterized by a stable planimetric configuration of the channel network. The structure of the channels and their watersheds is qualitatively similar to the Venice Lagoon''s ones. After the relatively fast ontogenetic phase, the subsequent morphological evolution of the bottom continues at a slower pace until a stable bathymetric configuration of the lagoon is reached. The model is able to reproduce the morphological effects of subsequent perturbations of natural or anthropogenic origin. [Copyright &y& Elsevier]

An intense cold air outbreak affected the northern Adriatic Sea during winter 2012, determining an exceptional persistence of northeasterly Bora wind over the basin, which lasted for about 3 weeks. The cold air coming from the Balkans produced icing in the Venice lagoon and very intense snowfall in the Apennines Mountains and even near the coasts. In order to understand the importance and role of air–sea interactions for the evolution of the atmospheric fields, simulations with the Weather Research and Forecasting (WRF) model encompassing the whole period have been performed using sea surface temperature (SST) fields with an increasing level of complexity. Starting from a large-scale static sea temperature, the SST in the initial and boundary conditions has been progressively made more realistic. First, a more refined field, retrieved from a satellite radiometer was used; then, the same field was updated every 6 h. Next, the effect of including a simplified 1D ocean model reproducing the Oceanic Mixed Layer (OML) evolution has been tested. Finally, the potential improvements coming from a coupled description of atmosphere–ocean and atmosphere–ocean–waves interactions have been explored within the Coupled Ocean–Atmosphere–Wave Sediment Transport (COAWST) modeling system. Results highlight that the energy exchange between air and sea does not significantly impact the atmospheric fields, in particular 10 m wind and 2 m temperature, also because of the geography of the basin and the predominance of synoptic-scale flow in intense events of Bora, in the northern Adriatic. However, when sensible and latent heat fluxes, which are dependent on atmospheric and oceanic variables, are analyzed, the more realistic representation of SST drastically improves the model performances. [ABSTRACT FROM AUTHOR]