Small scales matter: the role of submesoscale dynamics in large-scale ocean circulation and climate

• Grant number: 23/10506-0
• Support Opportunities: Research Grants - Young Investigators Grants
• Duration: February 01, 2024 - January 31, 2029
• Field of knowledge: Physical Sciences and Mathematics - Oceanography - Physical Oceanography
• Principal Investigator: César Barbedo Rocha
• Grantee: César Barbedo Rocha
• Host Institution: Instituto Oceanográfico (IO). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated researchers: Arjun G. Jagannathan ; Dante Campagnoli Napolitano ; Hector Torres ; John Thomas Farrar ; Paulo Henrique Rezende Calil
• Associated scholarship(s): 24/05528-8 - Submesoscale kinetic energy and tracer horizontal wavenumber spectra from saildrones, BP.IC; 24/03367-7 - The role of lateral shear in the development of submesoscale instabilities in the upper ocean, BP.MS; 24/03717-8 - Statistics of submesoscale fronts in the upper ocean, BP.IC

Abstract

The ocean plays a central role in Earth's changing climate. It has absorbed about 30% of carbon dioxide from burning fossil fuels in the industrial era and taken up, in the form of heat, about 90% of the radiation imbalance caused by the excess greenhouse gases, carbon dioxide included, that remained in the atmosphere. Global warming and its consequences thus depend crucially on the rates at which heat and carbon dioxide are absorbed at the air-sea interface, sequestered into the ocean interior, and redistributed across the global ocean. This in turn depends on eddying processes that stir and mix and transport heat, carbon and other tracers, whose physics are by and large poorly understood and whose models are largely divorced from robust in-situ measurements. This project focuses on a class of relatively small eddying processes called submesoscales -- fronts, instabilities and eddies with horizontal scales of several hundreds of meters to about 20 km. We will test the hypothesis that submesoscale phenomena in the upper ocean play an important role in large-scale ocean circulation and climate. To that end, we will analyze unprecedented observations of submesoscale flows that we recently collected as part of the Submesoscale Ocean Dynamics Experiment (SMODE) and of sea-surface height and derived geostrophic velocities from the recently launched Surface Water & Ocean Topography (SWOT) satellite mission. From SMODE velocity and water density measurements collected with an array of robotic sailboats traveling in submesoscale formation, we will calculate kinematic quantities such as vertical vorticity and horizontal divergence and estimate the vertical velocity across different submesoscale flows (fronts, instabilities, etc.). More important, we will use these data and analysis to inform the development and test the predictions of a hierarchy of theoretical and numerical models that we will develop with the goal of characterizing the lateral and vertical transport by submesoscale flows. These include idealized models with simple geometry and reduced equations (surface quasi-geostrophic model, stacked-Eady quasi-geostrophic model, Young-and-BenJellou model), models with simple geometry but full Boussinesq hydrostatic equations, and realistic submesoscale-resolving models in the Southwestern Atlantic. From the SWOT data, we will characterize the statistics and structure of submesoscale geostrophic velocities. SWOT geostrophic velocities will also be used to advect tracers and particles to estimate the eddy diffusivity due to balanced submesoscale flows. By the end of this project, we expect to produce a nuanced, quantitative characterization and physical understanding of submesoscale eddy transport, based on solid theoretical ground and constrained by in-situ observations. Such an understanding is crucial to developing physically meaningful parameterizations of submesoscale eddy transport in climate models, and therefore can pave the way for more accurate long-term climate forecasts. We also expect to produce a global estimate of the contribution of submesoscale phenomena to the total eddy transport in the global ocean. The project will support the Principal Investigator---a young scientist who was recently recruited back to Brazil after 9.5 years in the United States---to establish his research group at Universidade de São Paulo, starting a new research line in the country while maintaining his broad array of international collaborations. The project will fund two graduate and four undergraduate students, who will be trained in ocean and climate physics through cutting-edge research, learning skills highly valued in academic research and transferable to careers in industry. (AU)