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Publication
Characterization of circulation patterns in the Gulf of Cadiz based on satellite altimetry
Advisor(s)
Abstract(s)
Os dados de altimetria de satélite (1993-2020) são utilizados para analisar as correntes geostróficas e a Topografia Dinâmica Absoluta (ADT) do Golfo de Cádis (GoC). O estudo do ADT anual mostrou que a subida do nível do mar do GoC está bem dentro da tendência global. A análise sazonal do ADT e dos fluxos geostróficos mostrou um padrão bilateral. Nos meses de Verão, ocorrem fortes correntes equatoriais sobre a área da plataforma, enquanto que as correntes no interior do GoC são mais fracas. No Inverno, contudo, as correntes do Equador sobre a área da prateleira são mais fracas e mais fortes no interior do GoC. Dois mecanismos em particular poderiam ser identificados para estes padrões opostos: (1) a ocorrência de ventos fortes a norte, que formam frentes de afloramento sobre a plataforma no Verão, e (2) a Corrente dos Açores que atinge e influencia os fluxos no interior do GoC no Inverno.
Além disso, são explorados os efeitos das variações do nível da água nos padrões de circulação na plataforma norte do GoC. O ADT e as circulações são comparados com medições in situ utilizando medidores de marés e Perfis Acústicos de Corrente Doppler (ADCP), respectivamente. Foi demonstrado que o ADT tem correlações moderadas a boas com as medições de marés. Não foi possível encontrar correspondência clara entre a direcção do fluxo alongshore e o declive alongshore. Isto pode ser devido ao erro do ADT perto da costa.
Além disso, os dados do Radar de Alta Frequência (HFR) são utilizados para examinar a relação entre o ADT e a Corrente Contadora Costeira (CCC) estabelecida durante cinco exemplos com as mais fortes variações do ADT. Demonstra-se que o ADT era adequado para identificar gradientes de pressão alongshore desequilibrados, que são condutores plausíveis do CCC para os exemplos analisados. As medições do HFR revelaram que os fluxos de fluxo em direcção aos pólos atingem a sua velocidade máxima dois dias após a inclinação alongshore se tornar desequilibrada.
Satellite altimetry data (1993-2020) is used to analyze the geostrophic currents and Absolute Dynamic Topography (ADT) of the Gulf of Cadiz (GoC). The study of the annual ADT showed that the sea level rise of the GoC is well within the global trend. The seasonal analysis of ADT and geostrophic flows showed a bilateral pattern. In the summer months, strong equatorward currents occur over the shelf area, whereas the currents in the interior of the GoC are weaker. In winter, however the equatorward currents over the shelf area are weaker and stronger at the interior of the GoC. Two mechanisms in particular could be identified for these countervailing patterns: (1) the occurrence of strong northerly winds, which form upwelling fronts over the shelf in summer, and (2) the Azores Current which reaches and influences the flows in the interior of the GoC in winter. Further, the effects of water level variations on circulation patterns at the northern shelf of the GoC are explored. The ADT and circulations are compared with in situ measurements using tidal gauges and Acoustic Doppler Current Profiles (ADCP), respectively. It was shown that the ADT has moderate to good correlations to tidal gauge measurements. No clear correspondence between the alongshore flow direction and alongshore slope could be found. This might be due to the ADT error near the coast. Moreover, High Frequency Radar (HFR) data is used to examine the relation between ADT and Coastal Counter Current (CCC) set up during five examples with strongest ADT variations. It is shown that the ADT was suitable to identify unbalanced alongshore pressure gradients, which are plausible drivers of the CCC for the analyzed examples. The HFR measurements revealed that poleward flows reach their maximum velocity two days after the alongshore slope becomes unbalanced.
Satellite altimetry data (1993-2020) is used to analyze the geostrophic currents and Absolute Dynamic Topography (ADT) of the Gulf of Cadiz (GoC). The study of the annual ADT showed that the sea level rise of the GoC is well within the global trend. The seasonal analysis of ADT and geostrophic flows showed a bilateral pattern. In the summer months, strong equatorward currents occur over the shelf area, whereas the currents in the interior of the GoC are weaker. In winter, however the equatorward currents over the shelf area are weaker and stronger at the interior of the GoC. Two mechanisms in particular could be identified for these countervailing patterns: (1) the occurrence of strong northerly winds, which form upwelling fronts over the shelf in summer, and (2) the Azores Current which reaches and influences the flows in the interior of the GoC in winter. Further, the effects of water level variations on circulation patterns at the northern shelf of the GoC are explored. The ADT and circulations are compared with in situ measurements using tidal gauges and Acoustic Doppler Current Profiles (ADCP), respectively. It was shown that the ADT has moderate to good correlations to tidal gauge measurements. No clear correspondence between the alongshore flow direction and alongshore slope could be found. This might be due to the ADT error near the coast. Moreover, High Frequency Radar (HFR) data is used to examine the relation between ADT and Coastal Counter Current (CCC) set up during five examples with strongest ADT variations. It is shown that the ADT was suitable to identify unbalanced alongshore pressure gradients, which are plausible drivers of the CCC for the analyzed examples. The HFR measurements revealed that poleward flows reach their maximum velocity two days after the alongshore slope becomes unbalanced.
Description
Keywords
Análise Sazonal do ADT Fluxos geostróficos Fluxos Interior do GoC no inverno