Ocean-atmosphere interactions in the tropical Atlantic seasonal cycle and multidecadal variability of ENSO

The interaction between the ocean and atmosphere drives changes in the climate system in a wide variety of timescales. The strong annual cycle in the equatorial Atlantic, especially over the east, has been object of extensive research but the role of ocean-atmosphere interactions in driving the seasonal cycle remains to be fully understood in this region. The west African monsoon and the Atlantic cold tongue are the main phenomena controlling the seasonal variability in the equatorial Atlantic and a better understanding of their interaction is crucial for a complete comprehension of the dynamics of the annual cycle. Ocean atmosphere interactions are the main driver of ENSO, which is the leading mode of ocean-atmosphere variability at interannual timescales in the tropics. ENSO properties have experienced large changes in the last few decades but the drivers behind those changes are still in debate. The three studies presented in this thesis are based in climate model simulations. In the first and second papers the atmosphere and ocean components of NorESM model are used to investigate the dynamics of the seasonal cycle in the equatorial Atlantic. The third paper focuses on the identification of multidecadal modulation of ENSO properties by means of a strongly simplified model: the conceptual recharge oscillator model. The first part of this thesis presents an in-depth study of the mechanisms of the seasonal cycle in the equatorial Atlantic with special focus on the quantification of the role of the coupling between the ocean and the atmosphere. My results show that thermodynamic coupling is the main driver of the seasonal cycle in the western equatorial Atlantic and indicate that the dynamical Bjerknes feedback plays a secondary role. In the east, ocean dynamics and the monsoon are the main drivers of the seasonal cycle in the ocean and atmosphere, respectively, with ocean-atmosphere interactions contributing to the amplification of the annual cycle. In the second part of this thesis, I study the changes in observed ENSO properties at multidecadal timescales. The large observed changes in ENSO in the recent decades are reproduced with a conceptual model based on the recharge and discharge of the Pacific equatorial upper ocean heat content. This indicates that dynamic coupling is the main driver of ENSO in the last decades with the thermocline feedback being the mechanism responsible of the amplification of the SST anomalies in the eastern equatorial Pacific

Weakening of the Atlantic Niño variability under global warming

The Atlantic Nino is one of the most important patterns of interannual tropical climate variability, but how climate change will influence this pattern is not well known due to large climate model biases. Here we show that state-of-the-art climate models robustly predict a weakening of Atlantic Ninos in response to global warming, mainly due to a decoupling of subsurface and surface temperature variations as the upper equatorial Atlantic Ocean warms. This weakening is predicted by most (>80%) models in the Coupled Model Intercomparison Project Phases 5 and 6 under the highest emission scenarios. Our results indicate a reduction in variability by the end of the century by 14%, and as much as 24-48% when accounting for model errors using a simple emergent constraint analysis. Such a weakening of Atlantic Nino variability will potentially impact climate conditions and the skill of seasonal predictions in many regions. The Atlantic Nino is an important mode of tropical climate variability, but how it reacts to climate change is not well known due to model biases. Here the authors show a robust weakening of the Atlantic Nino of up to 24-48% under high emissions until the end of the century

Conflict transformation in indigenous' peoples territories: doing environmental justice with a 'decolonial turn'

One of the distinctive features of environmental justice theory in Latin America is its influence by decolonial thought, which explains social and environmental injustices as arising from the project of modernity and the ongoing expansion of a European cultural imaginary. The decolonization of knowledge and social relations is highlighted as one of the key challenges for overcoming the history of violent oppression and marginalization in development and conservation practice in the region. In this paper we discuss how conflict transformation theory and practice has a role to play in this process. In doing so, we draw on the Socio-environmental Conflict Transformation (SCT) framework elaborated by Grupo Confluencias, which puts a focus on building community capacity to impact different spheres of power: people and networks, structures and cultural power. We discuss this framework and its practical use in the light of ongoing experiences with indigenous peoples in Latin America. We propose that by strengthening the power of agency of indigenous peoples to impact each of these spheres it is possible to build constructive intra and intercultural relations that can help increase social and environmental justice in their territories and thus contribute to decolonizing structures, relations and ways of being

The James Webb Space Telescope Mission

Twenty-six years ago a small committee report, building on earlier studies, expounded a compelling and poetic vision for the future of astronomy, calling for an infrared-optimized space telescope with an aperture of at least $4m$. With the support of their governments in the US, Europe, and Canada, 20,000 people realized that vision as the $6.5m$ James Webb Space Telescope. A generation of astronomers will celebrate their accomplishments for the life of the mission, potentially as long as 20 years, and beyond. This report and the scientific discoveries that follow are extended thank-you notes to the 20,000 team members. The telescope is working perfectly, with much better image quality than expected. In this and accompanying papers, we give a brief history, describe the observatory, outline its objectives and current observing program, and discuss the inventions and people who made it possible. We cite detailed reports on the design and the measured performance on orbit.Comment: Accepted by PASP for the special issue on The James Webb Space Telescope Overview, 29 pages, 4 figure

Ocean-atmosphere interactions in the tropical Atlantic seasonal cycle and multidecadal variability of ENSO

The interaction between the ocean and atmosphere drives changes in the climate system in a wide variety of timescales. The strong annual cycle in the equatorial Atlantic, especially over the east, has been object of extensive research but the role of ocean-atmosphere interactions in driving the seasonal cycle remains to be fully understood in this region. The west African monsoon and the Atlantic cold tongue are the main phenomena controlling the seasonal variability in the equatorial Atlantic and a better understanding of their interaction is crucial for a complete comprehension of the dynamics of the annual cycle. Ocean atmosphere interactions are the main driver of ENSO, which is the leading mode of ocean-atmosphere variability at interannual timescales in the tropics. ENSO properties have experienced large changes in the last few decades but the drivers behind those changes are still in debate. The three studies presented in this thesis are based in climate model simulations. In the first and second papers the atmosphere and ocean components of NorESM model are used to investigate the dynamics of the seasonal cycle in the equatorial Atlantic. The third paper focuses on the identification of multidecadal modulation of ENSO properties by means of a strongly simplified model: the conceptual recharge oscillator model. The first part of this thesis presents an in-depth study of the mechanisms of the seasonal cycle in the equatorial Atlantic with special focus on the quantification of the role of the coupling between the ocean and the atmosphere. My results show that thermodynamic coupling is the main driver of the seasonal cycle in the western equatorial Atlantic and indicate that the dynamical Bjerknes feedback plays a secondary role. In the east, ocean dynamics and the monsoon are the main drivers of the seasonal cycle in the ocean and atmosphere, respectively, with ocean-atmosphere interactions contributing to the amplification of the annual cycle. In the second part of this thesis, I study the changes in observed ENSO properties at multidecadal timescales. The large observed changes in ENSO in the recent decades are reproduced with a conceptual model based on the recharge and discharge of the Pacific equatorial upper ocean heat content. This indicates that dynamic coupling is the main driver of ENSO in the last decades with the thermocline feedback being the mechanism responsible of the amplification of the SST anomalies in the eastern equatorial Pacific

Disentangling the impact of Atlantic Niño on sea-air CO2 flux

Abstract Atlantic Niño is a major tropical interannual climate variability mode of the sea surface temperature (SST) that occurs during boreal summer and shares many similarities with the tropical Pacific El Niño. Although the tropical Atlantic is an important source of CO2 to the atmosphere, the impact of Atlantic Niño on the sea-air CO2 exchange is not well understood. Here we show that the Atlantic Niño enhances (weakens) CO2 outgassing in the central (western) tropical Atlantic. In the western basin, freshwater-induced changes in surface salinity, which considerably modulate the surface ocean CO2 partial pressure (pCO2), are the primary driver for the observed CO2 flux variations. In contrast, pCO2 anomalies in the central basin are dominated by the SST-driven solubility change. This multi-variable mechanism for pCO2 anomaly differs remarkably from the Pacific where the response is predominantly controlled by upwelling-induced dissolved inorganic carbon anomalies. The contrasting behavior is characterized by the high CO2 buffering capacity in the Atlantic, where the subsurface water mass contains higher alkalinity than in the Pacific