Elisabet Rodríguez Cruz Padrões De Circulação Na Ría De Pontevedra
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Universidade de Aveiro Departamento de Física 2017 Elisabet Rodríguez Padrões de circulação na Ría de Pontevedra Cruz em situações de aoramento e afundamento Circulation patterns of Ría de Pontevedra under upwelling and downwelling conditions Universidade de Aveiro Departamento de Física 2017 Elisabet Rodríguez Padrões de circulação na Ría de Pontevedra Cruz em situações de aoramento e afundamento Circulation patterns of Ría de Pontevedra under upwelling and downwelling conditions Dissertação apresentada à Universidade de Aveiro para cumprimento dos requesitos necessários à obtenção do grau de Mestre em Ciências do Mar e da Atmosfera, realizada sob a orientação cientíca de Prof. Dr. Jesús Manuel Pedreira Dubert, Professor Auxiliar do Departamento de Física da Universidade de Aveiro e da Dra. Maria Rita Teixeira de Sampaio Nolasco, Investigadora da Universidade de Vigo e do CESAM. the jury / o júri president / presidente Prof. Doutor José Manuel Henriques Castanheira Professor Auxiliar da Universidade de Aveiro examiners committee / vogais Prof. Doutor Jesús Manuel Pedreira Dubert Professor Auxiliar da Universidade de Aveiro (Orientador) Prof. Doutor Joaquim Guilherme Henriques Dias Professor Auxiliar da Universidade de Lisboa Palavras-chave uxo; tempo de renovação; aoramento; afundamento; EOF; Ría de Pon- tevedra. Resumo Diversos estudos tem sido realizados sobre os padrões de circulação em algu- mas das Rías Baixas, mas este não é o caso da Ría de Pontevedra. Ao longo desta tese tentaremos completar os conhecimentos sobre esta Ría. Uma conguração do sistema ROMS-AGRIF foi utilizada neste estudo, sendo esta validada com base na comparação com dados de temperatura e salinidade medidos semanalmente pelo INTECMAR. A analise realizada baseia-se no estudo de três episódios representativos da circulação: um de aoramento e dois de afundamento, um destes com caudal do río Lérez signicativo. Foram ainda analisadas séries temporais de uxos e de tempos de renovação através de diversas secções. Foi analisada a correlação entre estas séries e os parâmetros forçadores (ventos e caudais dos rios). Foi realizado um estudo utilizando técnicas de funções empíricas ortogonais aplicado ao campo de velocidades normal às secções. Os eventos de aoramento são caracterizados por um reforço da circulação positiva na Ría, consistente com os uxos de saída pela camada superior e uxos de entrada pela camada inferior do canal principal da Ría, e com uxos de entrada pela boca norte e os uxos de saída pela boca sul. Nos eventos de afundamento o comportamento é oposto ao anterior. São dis- cutidas evidências de recirculação vertical em forma de células no sentido dos ponteiros do relógio na zona externa da Ría, associado à subdução de águas oceânicas que entram na Ría pela camada superior. Este fenómeno parece criar uma zona de bloqueio no meio do eixo da Ría, que pode ser um mecanismo responsável pelo desenvolvimento das denominadas marés vermelhas. Os uxos para o evento de afundamento são superiores aos dos eventos de aoramento. O tempo de renovação é próximo dos 2 dias para o afundamento e dos 4 dias para o aoramento. O estudo por funções empíricas ortogonais conrma a circulação descrita du- rante os episódios de aoramento e afundamento discutidos neste trabalho. A previsão das condições físicas na Ría de Pontevedra é importante para a compreensão dos processos associados ao desenvolvimento de marés vermel- has. Keywords ux; ushing time; upwelling; downwelling; EOF; Ría de Pontevedra. Abstract Circulation patterns inside some of the Rías Baixas have been widely studied, but this is not the case of the Ría de Pontevedra. Through this thesis, we try to enhance the knowledge about the circulation pattern of this Ría. A ROMS-AGRIF system conguration was used in this study. This congu- ration was validated through the comparison with weekly temperature and salinity data measured by INTECMAR. The analysis done in this work is based on the study of three representative events of the circulation patterns: one upwelling event and two downwelling events, one of them with Lérez river ow increase. Also, was analyzed temporal series of uxes and ushing times through the external mouths and the correlations between these series and the forcing parameters (winds and average of the rivers ow). An EOF's study was applied to the subinertial normal velocities at the sections. Upwelling events are characterized by a reinforcement of the positive estuar- ine circulation, consistent with surface layer outows and deep layer inows at the main channel of the Ría, and inows/outows at the north/south mouths. Downwelling events have an opposite behaviour to the event de- scribed before. There are evidences of the vertical mixing through clockwise circulations at the outer part of the Ría, associated with the ocean waters subduction that enter into the Ría through the surface layer. As a conse- quence, a blocking can be generated at the middle part of the Ría, which has been associated by other authors with the "red tides". Fluxes for downwelling events are higher than for upwelling events. Flushing times are around 2 days for downwelling and around 4 days for upwelling events. The EOF's study conrms the circulation described for upwelling and downwelling events, in this work. The forecast of the physical conditions at Ría de Pontevedra are important for the understanding of the processes behind the production of HABs. Contents 1 Introduction 1 1.1 Motivation . .1 1.2 Aims . .2 1.3 Work structure . .2 2 Study Area 3 2.1 The Galician Adjacent shelf: Rías Baixas . .3 2.2 Ría de Pontevedra . .4 2.2.1 Winds . .6 2.2.2 Circulation Patterns . .7 2.2.3 Water Mass . .8 2.2.4 Tides . .8 3 Methodology 11 3.1 Numerical Ocean Model . 11 3.1.1 Conguration . 14 3.2 Flux and Flushing Time: denition and computation . 16 3.3 Empirical Orthogonal Functions (EOFs) . 17 4 Results 19 4.1 Introduction . 19 4.2 Forcings . 19 4.2.1 Winds . 19 4.2.2 Rivers . 20 4.3 Model Validation . 21 4.4 Upwelling Event . 25 4.5 Downwelling Event . 28 4.6 Downwelling Event with River Inow Increases . 31 4.7 Flux and Flushing Time . 34 4.8 Empirical Orthogonal Functions (EOFs) . 36 5 Discussion 41 i ii CONTENTS 6 Conclusions 45 List of Figures 2.1 Map of the Ría de Pontevedra with some important locations. From Google Earth Pro . .4 2.2 Location map of the Ría de Pontevedra with bathymetry, sections and stations. Red lines indicate sections and red dots the stations. Black cross indicates the wind measurement point. Isobaths are shown at 10 m intervals, between 10 and 110 m. .5 2.3 Representation of an upwelling region illustrating the Ekman drift in the upper layer being replaced near the coast by upward-moving water from the lower- layer. The winds blows from the north to the south. Source: Mann and Lazier (2006). .7 3.1 Position of the variables in a s-coordinate system (a) on the Arakawa horizontal C-grid and (b) on the staggered vertical grid. From Penven Pierrick (2000). 13 3.2 Geographic location of (a) the large (LD), (b) rst (FD), second (SD) and third (TD) domains. The FD shows the 50, 500, 1000 and 2500 m bathymetric contours. 15 3.3 Along-ría section at Ría de Pontevedra. Isobaths are shown at 10 m intervals between 10 and 100 m. 16 4.1 Wind directions and intensities (m/s) each four hours. Positives values indi- cates southerly winds and negative values indicates northerly winds. (a) From January to June and (b) from July to December. 20 4.2 Time evolution of the river ow (m3=s) for Lérez (green), Verdugo (red) and Miño (blue) rivers. 21 4.3 Comparison of modelled (solid line) and measured (Intecmar; red star) tem- perature and salinity at (a) station P5 and (b) P9. (c,d) Measured (Intecmar) temperature and salinity (top row) and (c,d) modelled temperature and salinity (bottom row) at station P5. 23 4.4 Intensities and directions of wind (m/s) during July with the summer upwelling event (blue) represented. Positives values indicate a northward component and negative values indicate a southward component. 25 4.5 Subinertial velocities (cm/s) across sections and station P4 for July 12 at 13 hours. The depth of the arrows correspond to the scale of colors of the colorbar. 26 iii iv LIST OF FIGURES 4.6 Along-Ría section for salinity (a, c, e, g, i) and temperature (°C; b, d, f, h, j) data with along and vertical subtidal velocities (cm/s and mm/s; black arrows) on July 11, 12, 13, 14, 15. The sampling transect is shown in Figure 3.3. 28 4.7 Intensities and directions of wind (m/s) during the downwelling event (red). Positives values indicate a northward component and negative values indicate a southward component. 28 4.8 Subinertial velocities (cm/s) across sections and station P4 for August 26 at 13 hours. The depth of the arrows correspond to the scale of colors of the colorbar. 29 4.9 Along-Ría section for salinity (a, c, e, g, i, k) and temperature (°C; b, d, f, h, j, l) data with along and vertical subtidal velocities (cm/s and mm/s; black arrows) on August 24, 25, 26, 27 and 28. The sampling transect is shown in Figure 3.3. 31 4.10 Intensities and directions of wind (m/s) during the downwelling event with river ow increase. Positives values indicate a northward component and negative values indicate a southward component. 32 4.11 Subinertial velocities (cm/s) across sections and station P4 for April 30 at 13 hours. The depth of the arrows correspond to the scale of colors of the colorbar.