An advection-diffusion model to explain thermal surface anomalies off Cape Trafalgar

The authors describe an almost permanent thermal anomaly, with low surface-temperature values, off Cape Trafalgar. The existence of strong tidal currents in the alongshore direction, and the local offshore orientation of isobaths at this point, support the hypothesis of vertical forcing by interaction between the barotropic tide and topography. This is simplified for modelisation as the pass of a tidal current over a ridge, which is considered uniform in the crossshore direction. A bidimensional model in finite differences is developed to reproduce the main features observed experimentally. The combined effects of advection (both vertical and horizontal) and diffusion appear to be very important. The model is sensitive to the assumed values of thermal diffusion coefficients and their depth dependence, as well as to heat flux through the sea surface. To have realistic values for these parameters, a unidimensional diffusion model aimed at reproducing the mixed layer and thermocline observed in this area during summer has been developed. Heat flux and diffusion coefficients are adjustment parameters of the model, and, once determined, they are introduced in the 2-D advection-diffusion model. Results from simulation seem to be in good agreement with CTD observations, confirming our initial hypothesis.Se describe una anomalía térmica caracterizada por bajas temperaturas superficiales frente al cabo de Trafalgar. Debido a que la orientación de las isóbatas en esta área es casi perpendicular a la costa y a que existen fuertes corrientes de marea a lo largo de ella, se desarrolla la hipótesis de que la interacción entre las corrientes de marea y la topografía son los mecanismos responsables de esta anomalía. Para revisar esta hipótesis se desarrolla en el presente trabajo un modelo de advección-difusión que estudia el efecto del paso de una corriente de marea sobre un obstáculo. El modelo es sensible a ciertos parámetros, como los coeficientes de difusión térmica y el flujo de calor en la superficie del mar. Por ello desarrollamos un modelo monodimensional que reproduce la formación de la capa de mezcla y la termoclina estacional usando estos parámetros como parámetros de ajuste. Una vez encontrados los valores adecuados, son introducidos en el modelo de advección-difusión. Los resultados obtenidos parecen estar de acuerdo con los datos experimentales.Instituto Español de Oceanografí

Wafer-scale fabrication of high-quality tunable gold nanogap arrays for surface-enhanced Raman scattering

We report a robust and high-yield fabrication method for wafer-scale patterning of high-quality arrays of dense gold nanogaps, combining displacement Talbot lithography based shrink-etching with dry etching, wet etching, and thin film deposition techniques. By using the self-sharpening of -oriented silicon crystal planes during the wet etching process, silicon structures with extremely smooth nanogaps are obtained. Subsequent conformal deposition of a silicon nitride layer and a gold layer results in dense arrays of narrow gold nanogaps. Using this method, we successfully fabricate high-quality Au nanogaps down to 10 nm over full wafer areas. Moreover, the gap spacing can be tuned by changing the thickness of deposited Au layers. Since the roughness of the template is minimized by the crystallographic etching of silicon, the roughness of the gold nanogaps depends almost exclusively on the roughness of the sputtered gold layers. Additionally, our fabricated Au nanogaps show a significant enhancement of surface-enhanced Raman scattering (SERS) signals of benzenethiol molecules chemisorbed on the structure surface, at an average enhancement factor up to 1.5 x 10(6)

Challenges for Sustained Observing and Forecasting Systems in the Mediterranean Sea

The Mediterranean community represented in this paper is the result of more than 30 years of EU and nationally funded coordination, which has led to key contributions in science concepts and operational initiatives. Together with the establishment of operational services, the community has coordinated with universities, research centers, research infrastructures and private companies to implement advanced multi-platform and integrated observing and forecasting systems that facilitate the advancement of operational services, scientific achievements and mission-oriented innovation. Thus, the community can respond to societal challenges and stakeholders needs, developing a variety of fit-for-purpose services such as the Copernicus Marine Service. The combination of state-of-the-art observations and forecasting provides new opportunities for downstream services in response to the needs of the heavily populated Mediterranean coastal areas and to climate change. The challenge over the next decade is to sustain ocean observations within the research community, to monitor the variability at small scales, e.g., the mesoscale/submesoscale, to resolve the sub-basin/seasonal and inter-annual variability in the circulation, and thus establish the decadal variability, understand and correct the model-associated biases and to enhance model-data integration and ensemble forecasting for uncertainty estimation. Better knowledge and understanding of the level of Mediterranean variability will enable a subsequent evaluation of the impacts and mitigation of the effect of human activities and climate change on the biodiversity and the ecosystem, which will support environmental assessments and decisions. Further challenges include extending the science-based added-value products into societal relevant downstream services and engaging with communities to build initiatives that will contribute to the 2030 Agenda and more specifically to SDG14 and the UN's Decade of Ocean Science for sustainable development, by this contributing to bridge the science-policy gap. The Mediterranean observing and forecasting capacity was built on the basis of community best practices in monitoring and modeling, and can serve as a basis for the development of an integrated global ocean observing system