Submesoscale kinetic energy and tracer horizontal wavenumber spectra from saildrones

• Grant number: 24/05528-8
• Support Opportunities: Scholarships in Brazil - Scientific Initiation
• Start date: June 01, 2024
• End date: May 31, 2026
• Field of knowledge: Physical Sciences and Mathematics - Oceanography - Physical Oceanography
• Principal Investigator: César Barbedo Rocha
• Grantee: Lara Medeiros Schlumbom
• 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

Understanding the distribution of kinetic energy and tracer variance amongst spatial scales in the submesoscale range is critical to improving the representation of the effects of submesoscale flows in Earth Systems models. Yet such an understanding has been hindered by the paucity of submesoscale-resolving observations. To narrow this gap, this project will compute the mixed-layer horizontal wavenumber spectra from novel observations collected with saildrones (robotic sailboats) in two field experiments, one in the California Current region and the other in the North Brazil Current Retroflection region. In both experiments, several saildrones sampled velocity in the upper 100 m with an RD Instruments 300-kHz ADCP (Acoustic Doppler Current Profiler) and surface temperature/salinity data with a Seabird37 CTD (Conductive, Temperature and Depth profiler). The velocity data will be used to estimate kinetic-energy horizontal wavenumber spectra and the CTD data will be used to estimate tracer-variance horizontal wavenumber spectra. The kinetic-energy spectra will be decomposed into rotational and divergent components using a spectral Helmholtz decomposition and into wave and vortex components using a wave-vortex decomposition. Kinetic-energy and tracer variance spectra will be compared against spectra from realistic numerical simulations. The results will be interpreted in terms of existing theories for the energization of submesoscale flows and for tracer stirring at submesoscales. By producing a detailed spectral characterization of submesoscale-resolving observations in two dynamically different regions, we expect to contribute new insights into submesoscale stirring and mixing of tracers.