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ENSO Teleconnections Oscar Vergara Ventilation of the oceanic circulation in the Southeast Pacific by mesoscale activity and Rossby waves at interannual to decadal timescales : ENSO teleconnections Oscar Vergara To cite this version: Oscar Vergara. Ventilation of the oceanic circulation in the Southeast Pacific by mesoscale activity and Rossby waves at interannual to decadal timescales : ENSO teleconnections. Ocean, Atmosphere. Université Paul Sabatier - Toulouse III, 2017. English. NNT : 2017TOU30356. tel-02059950v2 HAL Id: tel-02059950 https://tel.archives-ouvertes.fr/tel-02059950v2 Submitted on 1 Feb 2019 HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. THTHESEESE`` En vue de l’obtention du DOCTORAT DE L’UNIVERSITE´ DE TOULOUSE D´elivr´e par : l’Universit´eToulouse 3 Paul Sabatier (UT3 Paul Sabatier) Prt ´esen ´ee et soutenue le 07/04/2017 par : Oscar Vergara Ventilation de la circulation oc´eaniquedans le Pacifique Sud-Est par les ondes de Rossby et l’activit´em´eso-´echelle : t´el´econnexionsd’ENSO. JURY Monsieur Peter Brandt Professeur d’Universit´e Rapporteur Monsieur Thierry Penduff Charg´ede Recherche CNRS Rapporteur Monsieur Boris Dewitte Directeur de Recherche IRD Directeur de th`ese Monsieur Nicholas Hall Professeur d’Universit´e Pr´esident du Jury Madame Angelique´ Melet Charg´eede Recherche Examinatrice Monsieur Oscar Pizarro Professeur d’Universit´e Examinateur Monsieur Marcel Ramos Directeur de Recherche Invit´e Ecol´ e doctorale et sp´ecialit´e : SDU2E : Oc´ean,Atmosph`ere et Surfaces Continentales Unit´e de Recherche : Laboratoire d’Etudes´ en G´eophysiqueet Oc´eanographie Spatiales (UMR 5566) Directeur de Th`ese : Boris Dewitte Rapporteurs : Peter Brandt et Thierry Penduff THTHESEESE`` En vue de l’obtention du DOCTORAT DE L’UNIVERSITE´ DE TOULOUSE D´elivr´e par : l’Universit´eToulouse 3 Paul Sabatier (UT3 Paul Sabatier) Prt ´esen ´ee et soutenue le 07/04/2017 par : Oscar Vergara Ventilation of the oceanic circulation in the Southeast Pacific by mesoscale activity and Rossby waves at interannual to decadal timescales: ENSO teleconnections. JURY Monsieur Peter Brandt Professeur d’Universit´e Rapporteur Monsieur Thierry Penduff Charg´ede Recherche CNRS Rapporteur Monsieur Boris Dewitte Directeur de Recherche IRD Directeur de th`ese Monsieur Nicholas Hall Professeur d’Universit´e Pr´esident du Jury Madame Angelique´ Melet Charg´eede Recherche Examinatrice Monsieur Oscar Pizarro Professeur d’Universit´e Examinateur Monsieur Marcel Ramos Directeur de Recherche Invit´e Ecol´ e doctorale et sp´ecialit´e : SDU2E : Oc´ean,Atmosph`ere et Surfaces Continentales Unit´e de Recherche : Laboratoire d’Etudes´ en G´eophysiqueet Oc´eanographie Spatiales (UMR 5566) Directeur de Th`ese : Boris Dewitte Rapporteurs : Peter Brandt et Thierry Penduff Acknowledgements I gratefully thank my advisor, Dr. Boris Dewitte, for his patience in guiding me through the unveiling of the present research subject, and his confidence in my work. I would also like to thank Dr. Oscar Pizarro, with whom I shared invaluable discussions about ocean dynamics and the challenges of being a researcher. I would also like to thank both rapporteurs, Pr. Peter Brandt and Dr. Thierry Penduff, for their construc- tive comments and suggestions that contributed to improve this thesis. My warm thanks to the whole of the LEGOS laboratory personnel, who pulled me through the dreadful amounts of paperwork needed every time I went abroad for a conference or field work, and also assisted me with every detail of the clerical aspects involved in conducting a thesis work. I couldn’t finish this manuscript without acknowledging the support and friend- ship that I was able to find among the PhD students, postdocs, interns and engineers at LEGOS. I thank you for your good mood and I will always treasure the good times shared along my PhD years. Last but not least, I would like to thank my family for their priceless support and inspiration which helped me complete this project. Finally, I would like to thank Chris- telle; without your constant backing and encouragement all of this would have not been possible. Your precious support helped me to endure the harshest moments of this work, and undeniably, part of it is as yours as it is mine. iii Contents Acknowledgements iii 1 Introduction 1 1.1 Wind-driven circulation . 2 1.2 The Humboldt Currents system . 3 1.2.1 Large scale circulation in the HCS . 4 1.2.2 The south Pacific Oxygen Minimum Zone . 8 1.2.3 Mesoscale features . 8 1.3 Teleconnection with the equatorial Pacific . 10 1.3.1 A brief description of El Niño . 12 1.3.2 The ENSO arrival at the Humboldt Currents System . 13 1.3.3 The connection between the equatorial Pacific and the deep east- ern Pacific . 14 1.4 ENSO diversity . 17 1.4.1 ENSO diversity trend . 18 1.5 Thesis motivations and objectives . 19 1.5.1 Scientific objectives and manuscript plan . 23 Introduction (français) . 25 2 Methodology and Observations 29 2.1 The regional ocean modeling system: ROMS . 29 2.1.1 Coordinate transformation . 31 2.1.2 Pressure gradient errors . 32 2.1.3 Spatial discretization and time stepping . 32 2.1.4 Advection scheme and mixing parametrization . 34 2.2 Long Rossby waves . 35 2.2.1 At the origin of long Rossby waves: the β-plane . 35 2.2.2 The dispersion relation for long Rossby waves . 36 2.2.3 Theoretical approach for vertically propagating Rossby waves . 39 2.2.4 Rossby wave energy flux . 41 Dissipation of the Rossby wave energy flux . 42 v 2.3 ENSO indices . 44 2.4 Observations . 46 2.4.1 Climatologies and reanalyses . 47 Simple Ocean Data Assimilation (SODA) reanalysis data set . 47 CSIRO Atlas of Regional Seas (CARS) . 48 ICOADS data set . 49 MetOffice temperature analyses . 49 2.4.2 Remote sensing data . 50 Sea Surface Temperature (SST) . 50 Sea Level Height (SLH) . 50 Chlorophyll-a . 51 2.4.3 In situ data . 52 Sea level stations . 52 ARGO floats data . 52 Currents . 53 3 Subthermocline variability in the South Eastern Pacific: interannual to decadal timescales 55 3.1 Overview . 55 3.2 Is it possible to use ARGO data to observe the long Rossby wave? . 56 3.2.1 Argo data set . 57 3.2.2 The equatorial Rossby wave . 57 3.2.3 The Extra-Tropical Rossby wave . 61 3.2.4 Conclusion . 61 3.3 Vertical energy flux at interannual to decadal timescales . 64 Résumé Article (français) . 93 3.4 Synthesis . 94 4 Ventilation of the South Pacific oxygen minimum zone: the role of the ETRW and mesoscale 97 4.1 Overview . 97 4.2 Seasonal variability of the oxygen minimum zone . 98 Résumé Article (français) . 121 4.3 Synthesis . 123 5 Conclusions and Perspectives 125 Conclusions et Perspectives (français) . 134 References 137 vi Abstract 157 Résumé 159 vii A mis padres. viii Chapter 1 Introduction In addition to hosting the most productive upwelling system in the world, the South Eastern Pacific (SEP) is subject to a rich variability at different timescales, due in part to the remote influence of the equatorial Pacific as well as to a prominent ocean-atmosphere interaction. Locally, the circulation in the SEP relates to a nearly year-round equatorward wind field, associated with the eastern rim of the South Pa- cific Anticyclone (Muñoz and Garreaud, 2005). This alongshore wind field propels the coastal upwelling of colder and nutrient-rich subsurface waters that fertilizes the eu- photic zone, and ultimately results in the high productivity found in the SEP (Strub et al., 1998). The conditions imposed by the local forcing in the SEP are also subject to the remote influence of the equatorial Kelvin waves (EKW) at a variety of timescales (cf. Shaffer et al., 1997; Pizarro et al., 2002; Pizarro and Montecinos, 2004), where the South American coast behaves as an extension of the equatorial waveguide and allows for the poleward propagation of coastally trapped Kelvin-like waves (Spillane et al., 1987), which con- nect the climate variability in the SEP to the tropical Pacific variability. In this manner, climatic events that take place in the tropical Pacific, such as the ENSO (El Niño South- ern Oscillation) events, reflect on the coastal circulation system in the SEP, modulating the local oceanographic and atmospheric conditions. Considering the high productiv- ity of the SEP in terms of fish catch, the occurrence of such events is intertwined with deep socioeconomic repercussions (cf. Cashin et al., 2014), which has motivated sev- eral international efforts to improve the current understanding of the SEP dynamics and its teleconnection with the tropical Pacific (e.g. VOCALS-VAMOS1, CLIVAR2 and TPOS20203 programs). Although observational efforts to monitor the SEP circulation are currently under- way, in situ subsurface observations remain sparse, which has prevented a full under- standing of the circulation in the region. In this context, the present work focuses on 1www.eol.ucar.edu 2www.clivar.org 3www.tpos2020.org 1 Chapter 1. Introduction the problem of the subsurface SEP circulation variability in connection with the vari- ability in tropical Pacific, based on regional oceanic modeling tools. The present chap- ter introduces the main aspects of the SEP circulation and variability, as well as the processes involved in the oceanic teleconnection between the SEP and the equatorial Pacific. Towards the end of the chapter, a brief description of the ENSO phenomenon and its diversity is made.
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