The role of lateral shear in the development of submesoscale instabilities in the upper ocean

• Grant number: 24/03367-7
• Support Opportunities: Scholarships in Brazil - Master
• Start date until: April 01, 2024
• End date until: March 31, 2026
• Field of knowledge: Physical Sciences and Mathematics - Oceanography - Physical Oceanography
• Principal Investigator: César Barbedo Rocha
• Grantee: Rafael Couto Martins
• Host Institution: Instituto Oceanográfico (IO). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Associated research grant: 23/10506-0 - Small scales matter: the role of submesoscale dynamics in large-scale ocean circulation and climate, AP.JP

Abstract

Studies in the past decade have revealed that upper-ocean submesoscale features, such as instabilities with horizontal scales of O(1) km, play a fundamental role in air-sea interactions, potentially impacting global climate. The generation of these features is sporadic, and their evolution is relatively rapid, ranging from a few hours to a few days, making direct observation of submesoscale phenomena is therefore challenging. In November 2022, the Intensive Operations Period 1 campaign of the Submesoscale Ocean Dynamics Experiment (SMODE-IOP1) sampled a frontogenetic submesoscale front in the California Current region, downstream of which mature instabilities approximately 10 km in size eventually developed. Motivated by these unprecedented observations, this project aims to describe the dynamics of the generation and evolution of submesoscale front instabilities, such as those observed in the SMODE-IOP1 campaign. This study's hypothesis is that horizontal shear is fundamental for the energization and evolution of submesoscale front instabilities. To test this hypothesis and achieve the main goal of this project, we will set up and execute computational simulations of the Boussinesq equations using the Oceananigans model. These simulations will be configured with initial conditions representing a submesoscale front in thermal-wind balance fitted to the observations collected during the SMODE-IOP1 campaign. The spatial structure of the emerging instabilities in the simulations will be identified through a Proper Orthogonal Decomposition (POD) analysis, and their results will be compared to data collected by saildrones (robotic sailboats) during the SMODE-IOP1 campaign, which measured the three-dimensional velocity structure of the finite-amplitude instabilities that developed downstream of the submesoscale front. The mechanisms involved in the process of generation, growth, maturation, and subsequent evolution of instabilities will be characterized through momentum and energy balance analyses. Finally, the vertical transport of tracers (heat, buoyancy anomaly, etc) and momentum will be estimated at different stages of the instabilities' evolution. This project will improve the understanding of the physics ocean submesoscale processes, potentially contributing to improve the representation of these phenomena in global climate models.