A comprehensive study of the marine currents of the Gulf of Uraba ´is presented for temporal scales ranging from intertidal to seasonal. The analyses made were based on three-dimensional (3D) numerical modeling and extensive current observations. The hydrodynamic model based on the Delft3D platform included the influence of different forcings such as tide, waves, atmosphere, river discharges, and density gradients. Because field data concerning these variables are scarce for the study area, measuring campaigns, in combination with global models and databases, were used to overcome this condition. The evaluation of the model was attained by the use of unprecedented field data obtained in different climatic seasons through a mobile gauge station. This station registered instantaneous vertical profiles of flow along 1200 km with approximately 50-m spacing. This type of measurement was preferred instead of those obtained from stationary stations, because the spatial gradients of the currents were much greater than their temporal variations. The good agreement of the 3D mathematical model in the reproduction of the observed instantaneous currents supported its use in defining the marine currents in the gulf. A combined analysis of the model results and the measured currents revealed a complex circulation pattern comprising simultaneously typical estuarine circulation, one-to three-layer flows, and even inverse circulation. This flow complexity would hardly have been determined through common measurement methodologies based on stationary gauge stations.

This paper deals with a methodology to quantitatively determine the effect of a number of coastal processes and external forcing on the hydrodynamics of the Urabá Gulf, which are preliminarily assumed to affect flow behavior. According to this purpose, a coupled flow-wave numerical simulation at the Uraba Gulf is performed by means of the Delft3D modeling system. The simulation includes the following processes: (i) the marine influence through the tidal forcing at the northern boundary of the Gulf; (ii) waves; (iii) thermal and salinity stratification; (iv) wind drag, and (v) fluvial influence through the discharges of the Atrato river and other secondary tributaries. The importance of a specific process and the region inside the Gulf where it is predominant, is defined through the proposed methodology. The analysis evidences the importance, and extended effect, of the Atrato river and the density currents on the magnitude of the flow velocities. Other processes are relevant over certain areas of the Gulf, which present special conditions, such as depth, energy, season, and coastal landforms, thus allowing them to stand out when compared to the main processes.

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The importance of near-surface faceted crystals in forming weak layers associated with snow avalanches has recently received greater attention. However, there is still much to be learned concerning the formation and growth of these crystal types, their geographical extent, and related avalanche activity. Here we report on a spatially extensive avalanche cycle that occurred during late September 1999 at high-elevations in the Bolivian Andes, claiming two lives. Climbers released one slide at about 5,300 m in the Cordillera Apolobamba (on El Presidente), and four days later snow scientists servicing a high-elevation meteorological site triggered another at 6,300 m near the summit of Illimani (Cordillera Real). Both slab avalanches followed lateral fracture propagation through 25-50 cm of relatively new snow; deeper pockets existed due to wind redistribution. Analysis of a snowpit on Illimani, from a nearby and safe location, showed that the avalanche ran on a thick layer of near-surface faceted crystals overlying the austral winter dry-season snow surface. Average size of the crystals was 5-7 mm, and individual crystals exceeded 10 mm in diameter. We evaluate local and regional meteorological information in an effort to understand what caused the growth of these large crystals and the resultant snowpack instability. Insights are offered regarding the avalanche hazard due to near-surface faceted crystal growth in high-elevation areas of the Tropics, where avalanches are not generally recognized as a significant hazard during the climbing season.

Several studies have been performed to determine the disease transmission potential of early bovine embryos. Most of them agree that the Zona Pellucida (ZP) is a barrier that generally protects the embryo from infection but can also be a potential route for the transmission of pathogens. This review will initially focus on the characteristics of the ZP and the potential ways in which an embryo can transmit disease and the possible alternatives to reduce this hazard.