Vertical Transport in Strain-Vorticity Space

Qiyu Xiao, New York University, New York, United States, Dhruv Balwada, Lamont -Doherty Earth Observatory, Palisades, NY, United States, K. Shafer Smith, New York University, Courant Institute of Mathematical Sciences, New York, NY, United States, Takaya Uchida, Columbia University of New York, Palisades, NY, United States and Ryan Abernathey, Lamont-Doherty Earth Observatory, Palisades, NY, United States
Submesoscale flows are often characterized by strong signals in vorticity, strain and surface divergence. Furthermore, a number of recent studies, both observational and modeling, have also shown that strong submesoscale flows are associated with localized regions of large vertical transport of tracers. This has lead to the hypothesis that submesoscale vertical transport might make for a large, unaccounted for, component of ventilation, nutrient and heat budgets in the ocean.

In our work we study the vertical transport in a high resolution idealized ocean model by transforming from geographical to strain-vorticity coordinates. This allows us to unambiguously quantify the transport that is associated with regions that are characterized locally as submesoscale flows, and contrast the contribution of these regions compared to more "quiescent" mesoscale flows. This transformation is a useful diagnostic tool, and allows a reduction in complexity of the turbulent flow. This is achieved as the statistics in the vorticity-strain coordinates are found to be temporally invariant. Our preliminary results show that while submesoscale flows create localized regions with strong fluxes, they do not have a disproportionately large contribution to the total flux of a passive tracer. However, these localized injections might still be important in fast time scale processes, such a phytoplankton blooms.