AbstractsBiology & Animal Science

Dynamics and variability of the alongshore flows on the northwestern iberian margin

by Ana Margarida Machado




Institution: Universidade de Lisboa
Department:
Year: 2014
Keywords: Oceanografia; Correntes marítimas; Anticiclones; Zonas costeiras; Península Ibérica; Teses de doutoramento - 2014
Record ID: 1324166
Full text PDF: http://www.rcaap.pt/detail.jsp?id=oai:repositorio.ul.pt:10451/11035


Abstract

Tese de doutoramento, Ciências Geofísicas e da Geoinformação (Oceanografia), Universidade de Lisboa, Faculdade de Ciências, 2014 This dissertation focuses on the Northwestern Iberian Margin, its seasonal and interannual variability, the vertical structure of the alongshore currents and the characteristics of the mesoscale field. These topics were explored by analyzing a 20-year simulation of the Regional Ocean Modeling System (ROMS) at 2.3 km resolution, forced by a 27 km resolution Weather Research and Forecast (WRF) winds (downscaled from Era-Interim reanalysis) covering the whole Western Iberian Margin. The model includes an explicit representation of the inflow/outflow at the Strait of Gibraltar in a nested grid system, and the climatological inflow of the main rivers. The model results are compared with various data. We show that currents over the slope are divided in three different cores: the Iberian Poleward Current (IPC), occupying the top 250 m, a deeper core at Mediterranean Water levels and in between the two, an equatorward core centered beneath the IPC core. The IPC is present almost yearlong, including in summer months, when it is close to the shelf-break and capped by the equatorward upwelling jet. After September, the IPC intensifies and its core surfaces. The main forcing mechanism of the IPC is the "Joint Effect of Baroclinicity and Relief" (JEBAR), but there is an important contribution from southerly winds in December and January, when the current is stronger and surface intensified. Regarding the interannual variability, we verified that the intensity of the IPC depends on the intensity of the southerly winds, from October to January. In September the intensity of the poleward flows depend on the larger scale wind stress curl, which changes JEBAR. We also show that the IPC transport has a strong variability at the synoptic scales, most of it forced by the wind. Short periods of relaxation of southerly winds are usually followed by the destabilization of the IPC and the origin of various anticyclones along the slope. A margem ocidental da Península Ibérica é uma região de grande interesse do ponto de vista oceanográfico devido à variedade de processos que a caracterizam e que acontecem a diferentes escalas espaciais e temporais. Na literatura esta região é particularmente conhecida por se situar no limite norte do sistema de afloramento das Canárias e por ser a região onde a Água Mediterrânica se difunde pelo Oceano Atlântico. Neste trabalho procurou-se contribuir para o conhecimento da circulação desta região, essencialmente através do desenvolvimento e análise de uma simulação numérica do oceano, de 20 anos, que cobre o período de 1989 a 2008. A simulação foi efectuada utilizando o modelo ROMS (Regional Ocean Modeling System) (Shchepetkin and McWilliams, 2005; Shchepetkin and McWilliams, 2003; Hedstrom, 2009), com uma resolução de 2.3 km e forçado por uma atmosfera que é uma saída do modelo atmosférico WRF, com 27 km de resolução e para o mesmo período. O modelo resolve explicitamente…