ENIDH – P - Artigo Científico
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- Long-Term Variability in Sea Surface Temperature and Chlorophyll a Concentration in the Gulf of CaliforniaPublication . López Martínez, Juana; Farach Espinoza, Edgardo Basilio; Cervantes, Hugo Herrera; García Morales, RicardoThe Gulf of California (GC) is the only interior sea in the Eastern Pacific Ocean and is the most important fishing area in the northwestern region of the Mexican Pacific. This study focuses on the oceanographic variability of the GC, including its southern portion, which is an area with a high flow of energy and exchange of properties with the Pacific Ocean (PO), in order to determine its role in physical–biological cycles and climate change. The purpose of this work is to analyze the sea surface temperature (SST) and chlorophyll a concentration (Chl-a) during the period from 1998–2022 as indicators of long-term physical and biological processes, oceanographic variability, and primary production in the GC. In total, 513 subareas in the GC were analyzed, and a cluster analysis was applied to identify similar areas in terms of SST and Chl-a via the K-means method and using the silhouette coefficient (>0.5) as a metric to validate the clusters obtained. The trends of the time series of both variables were analyzed, and a fast Fourier analysis was performed to evaluate cycles in the series. A descriptive analysis of the SST and Chl-a series showed that the SST decreased from south to north. Six bioregions were identified using a combined of both SST and Chl-a data. The spectral analysis of the SST showed that the main frequencies in the six bioregions were annual and interannual (3–7 years), and the frequencies of their variations were associated with basin-level weather events, such as El Niño and La Niña. The SST in the GC showed a heating trend at an annual rate of ~0.036 °C (~0.73 °C in 20 years) and a decrease in Chl-a at an annual rate of ~0.012 mg/m3 (~0.25 mg/m3 in 20 years), with potential consequences for communities and ecosystems. Additionally, cycles of 10–13 and 15–20 years were identified, and the 10–13-year cycle explained almost 40–50% of the signal power in some regions. Moreover, mesoscale features (eddies and filaments) were identified along the GC, and they were mainly associated with the clusters of the SST. All these spatial and temporal variabilities induce conditions that generate different habitats and could explain the high biodiversity of the GC. If the warming trend of the SST and the decreasing trend of the Chl-a continue in the long term, concerns could be raised, as they can have important effects on the dynamics of this important marine ecosystem, including habitat loss for numerous native species, declines in the catches of the main fishery resources, and, consequently, support for the arrival of harmful invasive species.
- Using a Tandem Flight Configuration between Sentinel-6 and Jason-3 to Compare SAR and Conventional Altimeters in Sea Surface Signatures of Internal Solitary WavesPublication . Magalhaes, Jorge M.; Lapa, Ian G.; Santos-Ferreira, Adriana M.; Silva, José C. B. da; Piras, Fanny; Moreau, Thomas; Amraoui, Samira; Passaro, Marcello; Schwatke, Christian; Hart-Davis, Michael; Maraldi, Claire; Donlon, CraigSatellite altimetry has been providing a continuous record of ocean measurements with numerous applications across the entire range of ocean sciences. A reference orbit has been used since 1992 with TOPEX/Poseidon, which was repeated in the Jason missions, and in the newly launched Sentinel-6 Michael Freilich (in November 2020) to continually monitor the trends of sea level rise and other properties of the sea surface. These multidecadal missions have evolved alongside major technological advances, whose measurements are unified into a single data record owing to continuous intercalibration and validation efforts. However, the new Sentinel-6 provides synthetic aperture radar (SAR) processing, which improves the along-track resolution of conventional altimeters from a few kilometres (e.g., for Jason-3) to about 300 m. This means a major leap in sampling towards higher frequencies of the ocean spectrum, which inevitably means reconciling the assumption of a uniform Brown surface between the footprints of the larger kilometre-scale conventional altimetry and those of the finer-scale SAR altimetry. To explore this issue, this study uses the vantage point of the Sentinel-6/Jason-3 tandem phase to compare simultaneous sea surface signatures of large-scale Internal Solitary Waves (ISWs) between SAR and conventional altimetry. These waves can modulate the sea surface into arrayed sections of increased and decreased roughness with horizontal scales up to 10 km, which inflict sharp transitions between increased and decreased backscatter in the radar altimeters. It is found that Sentinel-6 can provide more detailed structures of ISWs in standard level-2 products, when compared with those from the conventional Jason-3 (similarly to previous results reported from the SAR altimeter from Sentinel-3). However, a new and striking feature is found when comparing the radar backscatter between Sentinel-6 and Jason-3, which are in opposite phases in the ISWs. These intriguing results are discussed in light of the intrinsically different acquisition geometries of SAR and conventional altimeters as well as possible implications thereof.
- Spatial and temporal variability of mode-1 and mode-2 internal solitary waves from MODIS/TERRA sunglint off the Amazon shelfPublication . Macedo, Carina Regina de; Koch-Larrouy, Ariane; Silva, José Carlos Bastos da; Magalhães, Jorge Manuel; Lentini, Carlos Alessandre Domingos; Tran, Trung Kien; Rosa, Marcelo Caetano Barreto; Vantrepotte, VicentThe Amazon shelf is a key region for intense internal tides (ITs) and nonlinear internal solitary wave (ISWs) generation associated with them. The region shows well-marked seasonal variability (from March to July, MAMJJ, and from August to December, ASOND) of the circulation and stratification, which can both induce changes in the ISW physical characteristics. The description of the seasonal and neap–spring tidal variability in the ISWs off the Amazon shelf is performed for the first time using a meaningful data set composed of 140 MODIS-Terra imagery from 2005 to 2021, where about 500 ISW signatures were identified in the sun glint region. Previous studies have documented the existence of mode-1 ISWs, but the region appears as a newly described hotspot for mode-2 ISWs. ISW packets separated by typical mode-1 (95–170 km; 2.1–3.8 m s−1) and mode-2 (46–85 km; 1.0–1.9 m s−1) IT wavelengths have been identified and mapped coming from different IT generation sites. For each ISW, a group of waves (3 to 10) is generally follows the largest crest. The intra-packet distance between each wave in the group is about 10 to 20 km. Regions of higher occurrence of ISWs are spaced by a IT mode-1 wavelength. We make the assumption that it might correspond to the IT reflection beams at the surface, which may generate newer ISWs. The mean mode-1 and mode-2 inter-packet distances do not show significant differences according to their IT generation sites. The ISW activity is higher (more than 60 % of signatures) during spring tides than neap tides. In the region under the influence of the North Equatorial Counter Current (NECC), ISWs are separated by a mean mode-1 IT wavelength which is 14.3 % higher during ASOND than during MAMJJ due to a deeper thermocline and the reinforcement of the NECC. These ISWs are also characterized by a wider inter-packet distance distribution (higher standard deviation) that may be related to the stronger eddy kinetic energy (EKE) during ASOND compared to MAMJJ. The mean inter-packet distance of mode-2 ISWs remains almost unchanged during the two seasons, but the inter-packet distance distribution is wider in ASOND than in MAMJJ as for mode 1. Note that these results need to be treated with caution, as only few occurrences of mode-2 waves were found during MAMJJ. In the region of the NECC, the direction of propagation for all modes is very similar in MAMJJ (about 30∘ clockwise from the north), whereas, for ASOND, the ISWs propagate in a wider pathway (from 0 to 60∘ clockwise from the north), due to a much larger eddy activity. During ASOND, as the background flux goes further east, the inter-packet distances become larger (4 % for mode 1 and 7.8 % for mode 2). These results show that the reinforcement of the NECC in ASOND appears to play a role in diverting the waves towards the east, increasing their phase velocities and their eastern traveling direction component when compared to MAMJJ. Calculations of the IT velocities using the Taylor–Goldstein equation supported our results regarding the presence of ISWs associated with mode-2 ITs and additionally the IT seasonal variability.
- Nonlinear Internal Tides in a Realistically Forced Global Ocean SimulationPublication . Solano, Miguel S.; Buijsman, Maarten C.; Shriver, Jay F.; Magalhães, Jorge; Silva, Jorge da; Jackson, Christopher; Arbic, Brian K.; Barkan, Roy; AGUThe decay of the low-mode internal tide due to the superharmonic energy cascade is investigated in a realistically forced global Hybrid Coordinate Ocean Model simulation with 1/25° (4 km) horizontal grid spacing. Time-mean and depth-integrated supertidal kinetic energy is found to be largest near low-latitude internal tide generation sites, such as the Bay of Bengal, Amazon Shelf, and Mascarene Ridge. The supertidal kinetic energy can make up to 50% of the total internal tide kinetic energy several hundred kilometers from the generation sites. As opposed to the tidal flux divergence, the supertidal flux divergence does not correlate with the barotropic to baroclinic energy conversion. Instead, the time-mean and depth-integrated supertidal flux divergence correlates with the nonlinear kinetic energy transfers from (sub)tidal to supertidal frequency bands as estimated with a novel coarse-graining approach. The regular spaced banding patterns of the surface-intensified nonlinear energy transfers are attributed to semidiurnal mode 1 and mode 2 internal waves that interfere constructively at the surface. This causes patches where both surface tidal kinetic energy and nonlinear energy transfers are elevated. The simulated internal tide off the Amazon Shelf steepens significantly near these patches, generating solitary-like waves in good agreement with Synthetic Aperture Radar imagery. Globally, we find that regions of high supertidal energy flux also show a high correlation with observed instances of internal solitary waves.
- New physical and biological evidence of lateral transport affecting dinoflagellate cyst distribution in the benthic nepheloid layer along a land-sea transect off Figueira da Foz (Atlantic Iberian margin)Publication . García-Moreiras, I.; Hatherly, M.; Zonneveld, K.; Dubert, J.; Nolasco, R.; Santos, A. I.; Oliveira, A.; Moita, T.; Oliveira, P. B.; Magalhães, J. M.; Amorim, A.; Frontiers Media S.A.
- A method to extract the Quaternion Ship Domain parameters from AIS dataPublication . Silveira, P.; Teixeira, A. P.; Soares, C. GuedesThe ship domain concept is of great interest for ship traffic modelling, risk assessment and intelligent collision avoidance. The paper proposes and applies a method to define AIS data-based empirical polygonal ship domains, based on traffic density matrices that are derived around each reference ship from an AIS dataset. A modified Quaternion Ship Domain allowing for different shapes for each quadrant is proposed, which results in a better fitting to the empirical domain. The parameters of Quaternion Ship Domains that best fit the empirical polygonal domains are determined for cargo ships and tankers of different lengths. Violations of the Quaternion Ship Domain are then used as an indicator of collision risk that is graphically represented in the study area, providing important information to support maritime traffic monitoring and control tasks.
- A multicriteria outranking approach for ship collision risk assessmentPublication . Silveira, P.; Figueira, J. R.; Teixeira, A. P.; Soares, C. G.The paper presents a judgmental expert-based process to assess the ship collision risk using the ELECTRE Tri-nC multiple criteria outranking method. The approach first establishes a set of criteria deemed important by navigation experts, all of them experienced nautical officers, to assess the collision risk between two ships in open waters. A deck of cards-based method is then used to determine the weights of each criterion, according to the experts’ preferences. Finally, risk categories chosen by the experts are characterised in terms of multiple reference scenarios, also provided by the experts, and the ELECTRE Tri-nC method is used to assign validation scenarios to the risk categories. The results are compared with the experts’ assessments of the collision risk for the same scenarios and also with the individual assessments made by three experts that have not participated in the development of the decision model.
- O Impacto da Cibersegurança no Quadro Jurídico Regulatório da Segurança Marítima.Publication . Faria, D. LynceOs conceitos de segurança marítima e de proteção marítima tiveram na sua base diferentes finalidades, objetos e perspetivas. Contudo, atualmente, as mesmas convenções internacionais aplicáveis aos transportes marítimos regulam ambas as vertentes. Na análise da maioria dos incidentes e acidentes no mar é bastante difícil delimitar as matérias de segurança e de proteção e, normalmente, após uma avaria, é inútil fazê-lo já que o planeamento e a resposta aos riscos são normalmente dados de forma integrada. Por outro lado, assiste-se a uma progressiva extensão do conceito de segurança marítima para englobar as matérias da proteção em simultâneo com o aparecimento de um novo tipo de ameaças que estão sempre presentes desde o momento que se ligam os computadores às redes em qualquer lugar do mundo: as ciberameaças! Estando os navios equipados com novas avançadas tecnologias, a proteção contra os ciberataques é mais importante do que nunca. Estes avanços tecnológicos tornaram-se um alvo fácil e de alta prioridade para os criminosos cibernéticos. Com este comportamento, podem prosseguir o seu propósito de atacar os sistemas do navio e, a partir deles, os diferentes sistemas em terra. A digitalização da indústria marítima ocorreu de forma muito rápida. Contudo, tornou-se essencial para os marítimos não só compreenderem e adotarem estas novas tecnologias como, igualmente, assumirem uma postura cautelosa e de alerta de em relação a certos acontecimentos e ocorrências que podem correr perigosamente mal num curto espaço de tempo. Vislumbra-se um novo estádio da prontidão marítima que necessita de um robusto e bem definido “código” que alargue e concretize um “novo” conceito de segurança marítima em sentido lato que reforce as convenções internacionais marítimas e a sua aplicação. As responsabilidades dos “Estados de Bandeira” e dos “Estados do Porto”, nos termos do disposto na Convenção das Nações Unidas sobre o Direito do Mar e das convenções internacionais marítimas como se estabelece nos diferentes Memorandos de Entendimento ao nível mundial e nos documentos da OMI e de outras organizações internacionais (como a União Europeia), deverão ser atualizadas e passarem a considerar, também, as matérias da proteção marítima. Para além disso, é essencial apoiar uma cooperação estreita nos campos da segurança marítima e da proteção tendo e vista a elaboração de um novo e robusto “Código Marítimo”. Esta será a linha de orientação prosseguida, pretendendo-se, neste momento, “agitar e rolar” esta matéria rumo a um novo estádio regulatório
- Os novos desafios do serviço de pilotagemPublication . Castro, Miguel Vieira de
- O Direito Marítimo e a necessidade da sua uniformização – alguns tópicos para reflexãoPublication . Faria, Duarte Lynce