Papers by Marcello G Magaldi
Wintertime Fjord-Shelf Interaction in Southeast Greenland
EGU General Assembly Conference Abstracts, Apr 1, 2018
Running title:new Mediterranean mineralization rates for FOAM
mineralization rates on the fate of simulated aquaculture wastes
Lagrangian Simulations of Drifter Trajectories Adopting a New Explicit Expression for Eddy Diffusivities
Journal of Operational Oceanography, 2019
Disclaimer Informa UK Limited, trading as Taylor & Francis Group, make every effort to ensure the... more Disclaimer Informa UK Limited, trading as Taylor & Francis Group, make every effort to ensure the accuracy of all the information (the "Content") contained in our publications. However, Informa UK Limited, trading as Taylor & Francis Group, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Informa UK Limited, trading as Taylor & Francis Group. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Informa UK Limited, trading as Taylor & Francis Group, shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content.
PLOS ONE, 2019
Absolute and relative dispersion are fundamental quantities employed in order to assess the mixin... more Absolute and relative dispersion are fundamental quantities employed in order to assess the mixing strength of a basin. There exists a time scale called Lagrangian Integral Scale associated to absolute dispersion that highlights the occurrence of the transition from a quadratic dependence on time to a linear dependence on time. Such a time scale is commonly adopted as an indicator of the duration needed to lose the influence of the initial conditions. This work aims to show that in a semi-enclosed basin the choice of the formulation in order to calculate the absolute dispersion can lead to different results. Moreover, the influence of initial conditions can persist beyond the Lagrangian Integral Scale. Such an influence can be appreciated by evaluating absolute and relative dispersion recursively by changing the initial conditions. Furthermore, finite-size Lyapunov exponents characterize the different regimes of the basin.
Journal of Physical Oceanography, 2017
Initial results are presented from a yearlong, high-resolution (~2 km) numerical simulation cover... more Initial results are presented from a yearlong, high-resolution (~2 km) numerical simulation covering the east Greenland shelf and the Iceland and Irminger Seas. The model hydrography and circulation in the vicinity of Denmark Strait show good agreement with available observational datasets. This study focuses on the variability of the Denmark Strait overflow (DSO) by detecting and characterizing boluses and pulses, which are the two dominant mesoscale features in the strait. The authors estimate that the yearly mean southward volume flux of the DSO is about 30% greater in the presence of boluses and pulses. On average, boluses (pulses) are 57.1 (27.5) h long, occur every 3.2 (5.5) days, and are more frequent during the summer (winter). Boluses (pulses) increase (decrease) the overflow cross-sectional area, and temperatures around the overflow interface are colder (warmer) by about 2.6°C (1.8°C). The lateral extent of the boluses is much greater than that of the pulses. In both cases...
Ocean Science, 2018
The variability and evolution of the Northern Current (NC) in the area off Toulon is studied for ... more The variability and evolution of the Northern Current (NC) in the area off Toulon is studied for 2 weeks in December 2011 using data from a glider, a high-frequency (HF) radar network, vessel surveys, a weather station, and an atmospheric model. The NC variability is dominated by a synoptic response to wind events, even though the dataset also evidences early stages of transition from late summer to fallwinter conditions. With weak winds, the current is mostly zonal and in geostrophic balance even at the surface, with a zonal transport associated with the NC of ≈ 1 Sv. Strong westerly wind events (longer than 2-3 days) induce an interplay between the direct-wind-induced ageostrophic response and the geostrophic component: upwelling is observed, with offshore surface transport, surface cooling, flattening of the isopycnals, and reduced zonal geostrophic transport (0.5-0.7 Sv). The sea surface response to wind events, as observed by the HF radar, shows total currents rotated at ≈ −55 to −90 • to the right of the wind. Performing a decomposition between geostrophic and ageostrophic components of the surface currents, the wind-driven ageostrophic component is found to rotate by ≈ −25 to −30 • to the right of the wind. The ageostrophic component magnitude corresponds to ≈ 2 % of the wind speed.
Journal of Geophysical Research: Oceans, 2018
Glacier terminus regularly exposed to 0.5 TW of oceanic heat during winter. • Wind forcing freque... more Glacier terminus regularly exposed to 0.5 TW of oceanic heat during winter. • Wind forcing frequency a crucial parameter in determining magnitude of heat exchange. • Vertical mixing enhances buoyancy-driven overturning circulation.
Journal of Physical Oceanography, 2017
Seasonal variability in pathways of warm-water masses toward the Kangerdlugssuaq Fjord (KF)–Glaci... more Seasonal variability in pathways of warm-water masses toward the Kangerdlugssuaq Fjord (KF)–Glacier (KG) system, southeast Greenland, is investigated by backtracking Lagrangian particles seeded at the fjord mouth in a high-resolution regional ocean model simulation in the ice-free and the ice-covered seasons. The waters at KF are a mixture of Atlantic-origin water advected from the Irminger Basin [Faxaflói (FF)], the deep waters from the Denmark Strait, and the waters from the Arctic Ocean, both represented by the Kögur section (KO). Below 200-m depth, the warm water is a mixture of FF and KO water masses and is warmer in winter than in summer. The authors find that seasonal differences in pathways double the fraction of FF particles in winter, causing the seasonal warming and salinification. Seasonal temperature variations at the upstream sections (FF and KO) have a negligible impact on temperature variations near the fjord. Successful monitoring of heat flux to the fjord therefore...
Ocean Modelling, 2017
The Denmark Strait Overflow (DSO) is a major export route for dense waters from the Nordic Seas f... more The Denmark Strait Overflow (DSO) is a major export route for dense waters from the Nordic Seas forming the lower limb of the Atlantic Meridional Overturning Circulation, an important element of the climate system. Mixing processes along the DSO pathway influence its volume transport and properties contributing to the variability of the deep overturning circulation. They are poorly sampled by observations however which hinders development of a proper DSO representation in global circulation models. We employ a high resolution regional ocean model of the Irminger Basin to quantify impact of the mesoscale flows on DSO mixing focusing on geographical localization and local time-modulation of water property changes. The model reproduces the observed bulk warming of the DSO plume 100-200 km downstream of the Denmark Strait sill. It also reveals that mesoscale variability of the overflow ('DSO-eddies', of 20-30 km extent and a time scale of 2-5 day) modulates water property changes and turbulent mixing, diagnosed with the vertical shear of horizontal velocity and the eddy heat flux divergence. The spacetime localization of the DSO mixing and warming and the role of coherent mesoscale structures should be explored by turbulence measurements and factored into the coarse circulation models.
Scientific Reports, 2016
The Mediterranean Sea has been recently proposed as one of the most impacted regions of the world... more The Mediterranean Sea has been recently proposed as one of the most impacted regions of the world with regards to microplastics, however the polymeric composition of these floating particles is still largely unknown. Here we present the results of a large-scale survey of neustonic micro-and mesoplastics floating in Mediterranean waters, providing the first extensive characterization of their chemical identity as well as detailed information on their abundance and geographical distribution. All particles >700 μm collected in our samples were identified through FT-IR analysis (n = 4050 particles), shedding for the first time light on the polymeric diversity of this emerging pollutant. Sixteen different classes of synthetic materials were identified. Low-density polymers such as polyethylene and polypropylene were the most abundant compounds, followed by polyamides, plastic-based paints, polyvinyl chloride, polystyrene and polyvinyl alcohol. Less frequent polymers included polyethylene terephthalate, polyisoprene, poly(vinyl stearate), ethylene-vinyl acetate, polyepoxide, paraffin wax and polycaprolactone, a biodegradable polyester reported for the first time floating in off-shore waters. Geographical differences in sample composition were also observed, demonstrating sub-basin scale heterogeneity in plastics distribution and likely reflecting a complex interplay between pollution sources, sinks and residence times of different polymers at sea.
Turbulent Coherent Structures Near Coastal Capes
A numerical study aimed at investigating the conditions under which different flow regimes appear... more A numerical study aimed at investigating the conditions under which different flow regimes appear near coastal capes is presented. The impacts of the regimes are also quantified in terms of integral quantities like mixing, current transport and form drag. Idealized and realistic numerical simulations are run both in barotropically and baroclinically-driven systems. The realistic cases model the Western Adriatic Current (WAC) in the Adriatic Sea. In both cases, the turbulent state of the flow is controlled in first approximation by the Burger number, Bu. When a steady barotropic and geostrophic current impinges on a triangular idealized cape, vertical movements are strong for Bu < 0.1 and pronounced lee waves can be found downstream of the obstacle. For 0.1 less than or equal to Bu < 1, fluid parcels flow more around the obstacle than over it. Flow separation occurs and small tip eddies start to shed. For Bu greater than or equal to 1, tip eddies merge to form larger eddies in the lee of the cape. Flow regimes are also strongly dependent on the obstacle slope alpha when Bu greater than or equal to 1. Flow regime diagrams in the Bu-alpha space are determined. A baroclinic current as the WAC becomes unstable in absence of wind as it separates from the coast for the presence of capes along its path. Downwelling favorable winds narrow and thicken the coastal buoyant current, raising Bu above a critical value and suppressing baroclinic instabilities. Upwelling favorable winds enhance instabilities via the opposite mechanism. With downwelling winds waters mix but remain relatively fresh (S less than or equal to 38), while most of the freshwater signal is lost with upwelling winds. The along-shore transport increases with downwelling winds while it decreases and can even reverse with upwelling winds. The form drag calculated across the obstacles in the different simulations is at least twice the magnitude of skin friction. In barotropic conditions it increases with increasing Bu and decreasing alpha and an empirical parametrization in the Bu-alpha space is put forth. Across the Gargano Promontory, more symmetric pressure fields are observed with downwelling winds; the form drag decreases as a result. The opposite is registered with upwelling winds.
Observed and modeled surface Lagrangian transport between coastal regions in the Adriatic Sea with implications for marine protected areas
Continental Shelf Research, 2016
Abstract Surface drifters and virtual particles are used to investigate transport between seven c... more Abstract Surface drifters and virtual particles are used to investigate transport between seven coastal regions in the central and southern Adriatic Sea to estimate the degree to which these regions function as a network. Alongshore coastal currents and cyclonic gyres are the primary circulation features that connected regions in the Adriatic Sea. The historical drifter observations span 25 years and, thus, provide estimates of transport between regions realized by the mean surface circulation. The virtual particle trajectories and a dedicated drifter experiment show that southeasterly Sirocco winds can drive eastward cross-Adriatic transport from the Italian coast near the Gargano Promontory to the Dalmatian Islands in Croatia. Southeasterly winds disrupt alongshore transport on the west coast. Northwesterly Mistral winds enhanced east-to-west transport and resulted in stronger southeastward coastal currents in the western Adriatic current (WAC) and export to the northern Ionian Sea. The central Italian regions showed strong connections from north to south, likely realized by alongshore transport in the WAC. Alongshore, downstream transport was weaker on the east coast, likely due to the more complex topography introduced by the Dalmatian Islands of Croatia. Cross-Adriatic connection percentages were higher for east-to-west transport. Cross-Adriatic transport, in general, occurred via the cyclonic sub-gyres, with westward (eastward) transport observed in the northern (southern) arms of the central and southern gyres.
A numerical study aimed at investigating the roles of both the stratification and topographic slo... more A numerical study aimed at investigating the roles of both the stratification and topographic slope in generation of turbulent coherent structures in the lee of capes is presented. We consider a steady barotropic current impinging on an obstacle in a rotating and linearly-stratified environment. The obstacle is a triangular prism and represents an idealized headland extending from the coast. Numerical experiments are conducted at constant Rossby number Ro = 0.06, varying the Burger number, Bu, and the obstacle slope, α. Flow regime diagrams in the Bu − α space are determined. For Bu < 0.1, vertical movement over the obstacle is enhanced and a fully-attached regime with pronounced internal waves is established. For 0.1 ≤ Bu < 1, fluid parcels flow more around the obstacle than over it. Flow separation occurs and small tip eddies start to shed. For Bu ≥ 1, tip eddies merge to form larger eddies in the lee of the cape. We find that previous laboratory results cannot be used for gentler slopes, since bottom flow regimes are strongly dependent on α when Bu ≥ 1. The form drag coefficient exerted by the cape is at least two orders of magnitude larger than the one due to skin friction. It increases with increasing Burger numbers and decreasing slopes. When no separation occurs (low Bu), the increase with decreasing slopes is the result of the mixing associated with hydraulic phenomena. For intermediate and high Bu, form drag coefficients reach larger values as a result of the boundary layer mixing associated with flow separation. We put forth an empirical parametrization of form drag in the Bu − α space.
Preliminary assessment of the circulation induced by surface freshwater fluxes in HYCOM
Toward an integrated HF radar network in the Mediterranean Sea to improve search and rescue and oil spill response: the TOSCA project experience
Journal of Operational Oceanography, 2015
High-frequency (HF) coastal radars measure current velocity at the ocean surface with a 30–100 km... more High-frequency (HF) coastal radars measure current velocity at the ocean surface with a 30–100 km range and 1–3 km resolution, every 0.25–1 h. HF radars are well suited to many applications, such as search and rescue (SaR), oil-spill mitigation and ecosystem management. Here we present a first organized core of 12 HF radars installed in five sites in four countries (Greece, Italy, France and Spain) within the European MED project, the Tracking Oil Spill and Coastal Awareness (TOSCA) network. Dedicated experiments tested radar capabilities to estimate transport driven by currents, which is the key feature for all the above applications. Experiments involved the deployment of drifters, i.e., floating buoys, acting as proxies for substances passively advected by currents. Using HF radars the search range is reduced by a factor of 1.6 to 5.3 after 24 h. The paper also underlines the importance of sharing common tools for HF radar data processing and the need to mitigate radio frequency interference. The effort can be regarded as an initial step toward the creation of a Mediterranean or European HF radar network, crucial for any European integrated ocean observing system (IOOS).
Journal of Atmospheric and Oceanic Technology, 2015
This study investigates the results of blending altimetry-based surface currents in the Gulf of M... more This study investigates the results of blending altimetry-based surface currents in the Gulf of Mexico with available drifter observations. Here, subsets of trajectories obtained from the near-simultaneous deployment of about 300 Coastal Ocean Dynamics Experiment (CODE) surface drifters provide both input and control data. The fidelity of surface velocity fields are measured in the Lagrangian frame by a skill score that compares the separation between observed and hindcast trajectories to the observed absolute dispersion. Trajectories estimated from altimetry-based velocities provide satisfactory average results (skill score > 0.4) in large (~100 km) open-ocean structures. However, the distribution of skill score values within these structures is quite variable. In the DeSoto Canyon and on the shelf where smaller-scale structures are present, the overall altimeter skill score is typically reduced to less than 0.2. After 3 days, the dataset-averaged distance between hindcast and d...
The ISMAR high frequency coastal radar network: Monitoring surface currents for management of marine resources
OCEANS 2015 - Genova, 2015
The Institute of Marine Sciences (ISMAR) of the National Research Council of Italy (CNR) establis... more The Institute of Marine Sciences (ISMAR) of the National Research Council of Italy (CNR) established a High Frequency (HF) Coastal Radar Network for the measurement of the velocity of surface currents in coastal seas. The network consists of four HF radar systems located on the coast of the Gargano Promontory (Southern Adriatic, Italy). The network has been operational since May 2013 and covers an area of approximately 1700 square kilometers in the Gulf of Manfredonia. Quality Assessment (QA) procedures are applied for the systems deployment and maintenance and Quality Control (QC) procedures are performed on the data generation pipeline. The network provides hourly sea surface velocity data in realtime mode, that are published for visualization and access. In order to produce data in interoperable formats, according to the standards of Open Geospatial Consortium (OGC) for the access and delivery of geospatial data, a netCDF architecture has been defined on the basis of the Radiowave Operators Working Group (US ROWG) recommendations and compliant to the Climate and Forecast (CF) Metadata Conventions CF-1.6. The hourly netCDF files are automatically attached to a Thematic Real-time Environmental Distributed Data Services (THREDDS) catalog supporting OGC compliant distributions and protocols for data visualization, metadata interrogation and data download. HF radar data have been validated by comparison with velocities measured by drifters deployed within the radar coverage. The data produced by the ISMAR HF radar network are presently used in a number of applications, ranging from oil spill and SAR to fishery and coastal management applications.
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Papers by Marcello G Magaldi