Influence of topography on tide propagation and amplification in semi-enclosed basins

An idealized model for tide propagation and amplification in semi-enclosed rectangular basins is presented, accounting for depth differences by a combination of longitudinal and lateral topographic steps. The basin geometry is formed by several adjacent compartments of identical width, each having either a uniform depth or two depths separated by a transverse topographic step. The problem is forced by an incoming Kelvin wave at the open end, while allowing waves to radiate outward. The solution in each compartment is written as the superposition of (semi)-analytical wave solutions in an infinite channel, individually satisfying the depth-averaged linear shallow water equations on the f plane, including bottom friction. A collocation technique is employed to satisfy continuity of elevation and flux across the longitudinal topographic steps between the compartments. The model results show that the tidal wave in shallow parts displays slower propagation, enhanced dissipation and amplified amplitudes. This reveals a resonance mechanism, occurring when\ud the length of the shallow end is roughly an odd multiple of the quarter Kelvin wavelength. Alternatively, for sufficiently wide basins, also Poincaré waves may become resonant. A transverse step implies different wavelengths of the incoming and reflected Kelvin wave, leading to increased amplitudes in shallow regions and a shift of amphidromic points in the direction of the deeper part. Including the shallow parts near the basin’s closed end (thus capturing the Kelvin resonance mechanism) is essential to reproduce semi-diurnal and diurnal\ud tide observations in the Gulf of California, the Adriatic Sea and the Persian Gulf

Transport in an idealized three-gyre system with application to the Adriatic Sea

Author Posting. © American Meteorological Society, 2009. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 39 (2009): 675-690, doi:10.1175/2008JPO3975.1.Motivated by observations of surface drifters in the Adriatic Sea, transport in a three-gyre system is studied with the aid of dynamical systems techniques. Particular attention is paid to the issue of intergyre transport. The velocity field is assumed to be two-dimensional and incompressible and composed of a steady three-gyre background flow on which a time-dependent perturbation is superimposed. Two systems of this type are considered: 1) an observationally motivated, analytically prescribed model consisting of a steady background on which a multiperiodic time-dependent perturbation is superimposed, and 2) an observationally based model of the Adriatic Sea consisting of the mean surface circulation derived from surface drifter trajectories on which a time-dependent altimetry-based perturbation velocity field is superimposed. It is shown that for a small perturbation to the steady three-gyre background, two of the gyres exchange no fluid with the third gyre. When the perturbation strength exceeds a certain threshold, transport between all three gyres occurs. This behavior is described theoretically, illustrated using the analytic model and shown to be consistent with the observationally based model of the Adriatic. The relevance of the work presented to more complicated multiple-gyre problems is discussed.This work was supported by the National Science Foundation Grants CMG0417425 and CMG0825547

The Mediterranean Sea Regime Shift at the End of the 1980s, and Intriguing Parallelisms with Other European Basins

Background: Regime shifts are abrupt changes encompassing a multitude of physical properties and ecosystem variables, which lead to new regime conditions. Recent investigations focus on the changes in ecosystem diversity and functioning associated to such shifts. Of particular interest, because of the implication on climate drivers, are shifts that occur synchronously in separated basins. Principal Findings: In this work we analyze and review long-term records of Mediterranean ecological and hydro-climate variables and find that all point to a synchronous change in the late 1980s. A quantitative synthesis of the literature (including observed oceanic data, models and satellite analyses) shows that these years mark a major change in Mediterranean hydrographic properties, surface circulation, and deep water convection (the Eastern Mediterranean Transient). We provide novel analyses that link local, regional and basin scale hydrological properties with two major indicators of large scale climate, the North Atlantic Oscillation index and the Northern Hemisphere Temperature index, suggesting that the Mediterranean shift is part of a large scale change in the Northern Hemisphere. We provide a simplified scheme of the different effects of climate vs. temperature on pelagic ecosystems. Conclusions: Our results show that the Mediterranean Sea underwent a major change at the end of the 1980s that encompassed atmospheric, hydrological, and ecological systems, for which it can be considered a regime shift. We further provide evidence that the local hydrography is linked to the larger scale, northern hemisphere climate. These results suggest that the shifts that affected the North, Baltic, Black and Mediterranean (this work) Seas at the end of the 1980s, that have been so far only partly associated, are likely linked as part a northern hemisphere change. These findings bear wide implications for the development of climate change scenarios, as synchronous shifts may provide the key for distinguishing local (i.e., basin) anthropogenic drivers, such as eutrophication or fishing, from larger scale (hemispheric) climate drivers

Influence of Transparent Conductive Oxide on the Degradation of CdTe Solar Cell Performance

CdTe devices have reached a remarkable success in the market due to the robustness of the material and the simplicity of producing stoichiometric absorbers. For many years one of the strong limitations of this material was its high electron affinity that needs copper in the back contact degrading the cells. However a wide community of researchers has investigated and partially solved this issue, but very little has been done on the effect of the front contact on the degradation of the cells. In this paper we analyze the effect of different TCOs on the stability of CdTe solar cells. Solar cell efficiencies show similar values but with some differences in Jsc, mostly due to the effect on the transmission spectra. However most interesting results come from the analysis of the capacitance-voltage and drive level capacitance profiling and from the aging of the different devices. Results show a different distribution of the defects for the solar cells with ITO front contact, compared to ITO/ZnO based devices. This difference is confirmed also by the aging results in open circuit, CV-DLCP measurements suggests diffusion of impurities from the glass/ITO stack

Influence of Transparent Conductive Oxide on the Degradation of CdTe Solar Cell Performance

CdTe devices have reached a remarkable success in the market due to the robustness of the material and the simplicity of producing stoichiometric absorbers. For many years one of the strong limitations of this material was its high electron affinity that needs copper in the back contact degrading the cells. However a wide community of researchers has investigated and partially solved this issue, but very little has been done on the effect of the front contact on the degradation of the cells. In this paper we analyze the effect of different TCOs on the stability of CdTe solar cells. Solar cell efficiencies show similar values but with some differences in Jsc, mostly due to the effect on the transmission spectra. However most interesting results come from the analysis of the capacitance-voltage and drive level capacitance profiling and from the aging of the different devices. Results show a different distribution of the defects for the solar cells with ITO front contact, compared to ITO/ZnO based devices. This difference is confirmed also by the aging results in open circuit, CV-DLCP measurements suggests diffusion of impurities from the glass/ITO stack