Energy Cascade and Dynamics of Internal Waves on a Subtropical Continental Shelf

• Grant number: 25/08224-2
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate (Direct)
• Start date: April 01, 2026
• End date: March 31, 2027
• Field of knowledge: Physical Sciences and Mathematics - Oceanography - Physical Oceanography
• Principal Investigator: Marcelo Dottori
• Grantee: Arian Dialectaquiz Santos
• Supervisor: Piero Luigi Fernandes Mazzini
• Host Institution: Instituto Oceanográfico (IO). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: Virginia Institute Of Marine Science, United States
• Associated to the scholarship: 22/16352-2 - Internal waves and their influence on the oceanic thermodynamics of the Alcatrazes Archipelago, BP.DD

Abstract

During the summer of 2002-a period representative of typical summer stratification-internal waves were observed in the South Brazil Bight (SBB), coinciding with the upwelling of Atlantic Central Water and the dynamics of Internal Tides, with the M2 frequency contributing approximately 10% of the energy spectrum. Using the Regional Ocean Modelling System (ROMS) at a horizontal resolution of 1 km, we examine the generation and interaction of Internal Tides within the SBB, identifying substantial spatial variability. Offshore energy hotspots are influenced by supercritical topography, local topographic features, and the Brazil Current, with 8.70% of all 5.204 GW converted energy-concentrated along the slope- comprising only 1.64% of the area. The topographic features and the Brazil Current trap extend the residence time of the Mode-1 M2 Internal Tide by five days beyond theoretical predictions, amplifying nonlinear interactions. At this level, wave-wave interactions become as significant as wave-mean flow interactions, transferring energy to higher frequencies and sustaining baroclinic energy in shallower waters, where stratification rapidly weakens. Approximately 16.18% of the M2 energy transferred from barotropic to baroclinic cascades to higher harmonics, while 63.73% reflects back. Scattered energy supports weakly coherent internal waves at depths shallower than 200 m, creating a nearly closed energy budget in the model. The Internal Tide enhances vertical mixing diffusivity by up to 21%, primarily near the seabed, and increases cold-water advection and thermal diffusivity coefficients, while reducing the vertical temperature gradient, particularly at the surface and subsurface levels. To expand these results, the here presented project aims to explore the role of wind-driven internal waves and their interactions with the Brazil Current in enhancing mixing, with emphasis on topographic conversion hotspots and remote internal wave reflections, through modelling via ROMS, a model which the Virginia Institute of Marine Sciences has vast expertise and network, especially concerning wind-driven processes, and fine-scale parametrizations.