arXiv subjects

Sandro Carniel

Publications and source records attributed to Sandro Carniel.

6 recordsLinked to original sources

arXiv2025

Rotational and Irrotational Wind Forcing as dual drivers of El Nino Southern Oscillation variability

El Ni\~no Southern Oscillation (ENSO) is the Earth's strongest source of interannual climate variability. Although its center of action is in the tropical Pacific, it has significant influences on the climate at the planetary scale. ENSO is sustained by a feedback process between equatorial winds, vertical displacements of the thermocline, and sea surface temperature (SST) anomaly gradients. This produces an oscillation in the SST anomaly between a warm (El Ni\~no) and a cold phase (La Ni\~na). While the natural time-scale of ENSO variability is interannual, variations in its behavior and characteristics have been observed over longer time scales, including decadal and interdecadal. Here, we use the Helmholtz decomposition to break down the wind stress into two components: irrotational (curl free) and solenoidal (divergence free). We show that the irrotational component of the wind stress drives the dynamics of the thermocline on the interannual time-scale, while the solenoidal component, whose action is influenced by the stratification of the water column, affects the variability of the thermocline over decadal or interdecadal time-scales. Furthermore, we develop an integral relation that links the variability of the thermocline depth anomaly across the entire tropical Pacific to the variability of the average SST anomaly in the central tropical Pacific (known as the Ni\~no-3.4 index) and conclude that the irrotational component of the wind stress determines the interannual variability of the Ni\~no-3.4 index, while the solenoidal component determines its long-term variability.

physics.ao-ph↗

arXiv2023

Monitoring of Underwater Critical Infrastructures: the Nord Stream and Other Recent Case Studies

The explosions on September 26th, 2022, which damaged the gas pipelines of Nord Stream 1 and Nord Stream 2, have highlighted the need and urgency of improving the resilience of Underwater Critical Infrastructures (UCIs). Comprising gas pipelines and power and communication cables, these connect countries worldwide and are critical for the global economy and stability. An attack targeting multiple of such infrastructures simultaneously could potentially cause significant damage and greatly affect various aspects of daily life. Due to the increasing number and continuous deployment of UCIs, existing underwater surveillance solutions, such as Autonomous Underwater Vehicles (AUVs) or Remotely Operated Vehicles (ROVs), are not adequate enough to ensure thorough monitoring. We show that the combination of information from both underwater and above-water surveillance sensors enables achieving Seabed-to-Space Situational Awareness (S3A), mainly thanks to Artificial Intelligence (AI) and Information Fusion (IF) methodologies. These are designed to process immense volumes of information, fused from a variety of sources and generated from monitoring a very large number of assets on a daily basis. The learned knowledge can be used to anticipate future behaviors, identify threats, and determine critical situations concerning UCIs. To illustrate the capabilities and importance of S3A, we consider three events that occurred in the second half of 2022: the aforementioned Nord Stream explosions, the cutoff of the underwater communication cable SHEFA-2 connecting the Shetland Islands and the UK mainland, and the suspicious activity of a large vessel in the Adriatic Sea. Specifically, we provide analyses of the available data, from Automatic Identification System (AIS) and satellite data, integrated with possible contextual information, e.g., bathymetry, weather conditions, and human intelligence.

eess.SP↗

arXiv2021

COVID-19 Impact on Global Maritime Mobility

To prevent the outbreak of the Coronavirus disease (COVID-19), many countries around the world went into lockdown and imposed unprecedented containment measures. These restrictions progressively produced changes to social behavior and global mobility patterns, evidently disrupting social and economic activities. Here, using maritime traffic data collected via a global network of AIS receivers, we analyze the effects that the COVID-19 pandemic and containment measures had on the shipping industry, which accounts alone for more than 80% of the world trade. We rely on multiple data-driven maritime mobility indexes to quantitatively assess ship mobility in a given unit of time. The mobility analysis here presented has a worldwide extent and is based on the computation of: CNM of all ships reporting their position and navigational status via AIS, number of active and idle ships, and fleet average speed. To highlight significant changes in shipping routes and operational patterns, we also compute and compare global and local density maps. We compare 2020 mobility levels to those of previous years assuming that an unchanged growth rate would have been achieved, if not for COVID-19. Following the outbreak, we find an unprecedented drop in maritime mobility, across all categories of commercial shipping. With few exceptions, a generally reduced activity is observable from March to June, when the most severe restrictions were in force. We quantify a variation of mobility between -5.62% and -13.77% for container ships, between +2.28% and -3.32% for dry bulk, between -0.22% and -9.27% for wet bulk, and between -19.57% and -42.77% for passenger traffic. This study is unprecedented for the uniqueness and completeness of the employed dataset, which comprises a trillion AIS messages broadcast worldwide by 50000 ships, a figure that closely parallels the documented size of the world merchant fleet.

econ.GN↗

arXiv2020

Space-based Global Maritime Surveillance. Part I: Satellite Technologies

Maritime surveillance (MS) is crucial for search and rescue operations, fishery monitoring, pollution control, law enforcement, migration monitoring, and national security policies. Since the early days of seafaring, MS has been a critical task for providing security in human coexistence. Several generations of sensors providing detailed maritime information have become available for large offshore areas in real time: maritime radar sensors in the 1950s and the automatic identification system (AIS) in the 1990s among them. However, ground-based maritime radars and AIS data do not always provide a comprehensive and seamless coverage of the entire maritime space. Therefore, the exploitation of space-based sensor technologies installed on satellites orbiting around the Earth, such as satellite AIS data, synthetic aperture radar, optical sensors, and global navigation satellite systems reflectometry, becomes crucial for MS and to complement the existing terrestrial technologies. In the first part of this work, we provide an overview of the main available space-based sensors technologies and present the advantages and limitations of each technology in the scope of MS. The second part, related to artificial intelligence, signal processing and data fusion techniques, is provided in a companion paper, titled: "Space-based Global Maritime Surveillance. Part II: Artificial Intelligence and Data Fusion Techniques" [1].

eess.SP↗

arXiv2020

Space-based Global Maritime Surveillance. Part II: Artificial Intelligence and Data Fusion Techniques

Maritime surveillance (MS) is of paramount importance for search and rescue operations, fishery monitoring, pollution control, law enforcement, migration monitoring, and national security policies. Since ground-based radars and automatic identification system (AIS) do not always provide a comprehensive and seamless coverage of the entire maritime domain, the use of space-based sensors is crucial to complement them. We reviewed space-based technologies for MS in the first part of this work, titled "Space-based Global Maritime Surveillance. Part I: Satellite Technologies" [1]. However, future MS systems combining multiple terrestrial and space-based sensors with additional information sources will require dedicated artificial intelligence and data fusion techniques for the processing of raw satellite images and fuse heterogeneous information. The second part of our work focuses on the most promising artificial intelligence and data fusion techniques for MS using space-based sensors.

eess.SP↗

arXiv2014

A review of modeling applications using ROMS model and COAWST system in the Adriatic sea region

From the first implementation in its purely hydrodynamic configuration, to the last configuration under the Coupled Ocean-Atmosphere-Wave-Sediment Transport (COAWST) system, several specific modelling applications of the Regional Ocean Modelling Systems (ROMS, www.myroms.org) have been put forward within the Adriatic Sea (Italy) region. Covering now a wide range of spatial and temporal scales, they developed in a growing number of fields supporting Integrated Coastal Zone Management (ICZM) and Marine Spatial Planning (MSP) activities in this semi-enclosed sea of paramount importance including the Gulf of Venice. Presently, a ROMS operational implementation provides every day hydrodynamic and sea level 3-days forecasts, while a second one models the most relevant biogeochemical properties, and a third one (two-way coupled with the Simulating Waves Nearshore (SWAN) model) deals with extreme waves forecast. Such operational models provide support to civil and environmental protection activities (e.g., driving sub-models for oil-spill dispersion, storm surge, coastal morphodynamic changes during storms, saline wedge intrusion along Po River), in a growing context of stake-holders at regional, national and international level. Besides, ROMS and COAWST research based activities are also carried out, mostly aiming at investigating sediment transport, eggs and larvae dispersion, hypoxic events in the basin; through successive nesting very high resolutions nearshore the Italian coast can be reached, allowing to simulate river mouth environments and artificial reefs. Resulting outputs, written in NetCDF CF compliant format, are delivered via THREDDS Data Server to a growing number of users around the world.

physics.ao-ph↗