The Role of Horizontal Shear in the Evolution of Submesoscale Mixed-Layer Instabilities: An Exploration of the Parameter Space

• Grant number: 25/05959-1
• Support Opportunities: Scholarships abroad - Research Internship - Master's degree
• Start date: June 01, 2025
• End date: November 15, 2025
• Field of knowledge: Physical Sciences and Mathematics - Oceanography - Physical Oceanography
• Principal Investigator: César Barbedo Rocha
• Grantee: Rafael Couto Martins
• Supervisor: Jonathan Gula
• Host Institution: Instituto Oceanográfico (IO). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: Laboratoire D'Océanographie Physique Et Spatiale, France
• Associated to the scholarship: 24/03367-7 - The role of lateral shear in the development of submesoscale instabilities in the upper ocean, BP.MS

Abstract

Studies over the past decade have revealed that submesoscale features in the upper ocean, such as instabilities with a horizontal scale of O(1) km, play a fundamental role in ocean-atmosphere interactions and can impact the global climate. The formation of these features is sporadic, and their evolution is relatively rapid, occurring over a few hours to a few days, making direct observations of submesoscale phenomena a challenging endeavor. 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 length eventually developed. Motivated by these unprecedented observations, this project aims to describe the dynamics of the formation and evolution of submesoscale front instabilities, such as those observed during the SMODE-IOP1 campaign. This study hypothesizes that horizontal shear is fundamental to the energization and evolution of submesoscale front instabilities. To test this hypothesis and achieve the main objective of this project, computational simulations of the Boussinesq equations are being developed using the Oceananigans model. The current simulations intend to reproduce the observed dynamics, configured with initial conditions based on the in-situ data, representing a submesoscale front in thermal wind balance. Besides these control simulations, in this project, we intend to run different simulation configurations varying some key parameters, related to horizontal shear and vertical shear, and study the impact of this variation in the generation and growth of the instabilities. The mechanisms involved in the generation, growth, maturation, and subsequent evolution of these instabilities will be characterized through momentum and energy balance analyses and the results will be compared to data collected by saildrones (autonomous sailing robots) during the SMODE-IOP1 campaign, which measured the three-dimensional velocity structure of the finite-amplitude instabilities that developed downstream of the submesoscale front. This project will deepen our understanding of the phenomenology and consequences of oceanic submesoscale processes, potentially contributing to the improved representation of these phenomena in global climate models.