Lagrangian evolution of bottom boundary-generated potential vorticity anomalies and their controls on submesoscale flows and mixing in the interior
Abstract
Improving our ability to predict and observe submesocale flows in the ocean interior is one of the next grand challenges in physical oceanography. In the upper ocean we have made great inroads in these tasks in part using Lagrangian methods informed by the theoryof potential vorticity (PV) dynamics. The PV approach has demonstrated skill in predicting where and when submesoscale turbulence forms, in understanding its dynamical evolution, and in quantifying its effect on turbulent mixing. The goal of this proposal is to extend what we have learned in the upper ocean and adapt it to the interior to study the Lagrangian evolution of submesoscale PV anomalies generated by the interaction of larger-scale currents with topography. The emphasis will be on wakes of low PV fluid shed from headlands, seamounts, or abrupt changes in topography which preliminary simulations and observational analyses show can lead to anactive submesoscale wake. This includes the generation of submesoscale symmetric (SI) and centrifugal (CI) instabilities, which canmodify both the dynamical and turbulent properties of the interior flow, but which also in the interior have many open questions intheir Lagrangian lifecycle from generation to dissipation. We propose that topographic wakes can be usefully organized#particularlyfor field campaign planning purposes#into two dynamical regions, first a nearfield CI/SI stabilization region, where the PV is returned to near-zero by SI/CI, and then further downstream a vortex formation region where the low PV anomalies coalesce into submesoscale coherent vortices (SCV). Each of these regions are associated with distinct open questions as to their dynamics, turbulent properties, and optimal observing strategies which will be addressed in the course of this work. To accomplish this we will use theory paired with high-resolution regional and large-eddy simulations (LES) to characterize the Lagrangian evolution of submesoscale PV anomalies and small-scale turbulence that form in CI/SI stabilization and vortex formation regions and their dependence on larger-scale currents, topography, and stratification. The regional simulations will ultimately target the sites of the RIOT field campaigns, butas interim areas of interest we will focus on either the continental slope north of Alaska into the Beaufort Gyre, where there is observational evidence of CI stabilization and vortex formation in the interior, or the New England Seamount Chain where the Gulf Stream can generate an eddying interior wake. Exploration of the fundamental parameter space, including the effects of smaller-scale topographic variations, and the two-way coupling between 3D turbulence and the submesoscales will be studied with LES. The regional simulations and LES will both be used to help plan the field campaigns by identifying locations where CI/SI stabilization and vortex formation regions are likely to be found#including identifying the essential controlling parameters#and by characterizing key submesoscale phenomena of interest. In addition, they will be used to run Lagrangian-based OSSEs to help design sampling strategies for optimally observing these phenomena. Post-cruise idealized process simulations configured with flow parameters representative of the observations will be performed to aid in the interpretation of the measurements and to delve into the governing physics. This work is a collaborative effort between Leif Thomas (Stanford) and Jacob Wenegrat (UMD), who have submitted identical project narratives.Approved for public release.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 09, 2024
- Source ID
- N000142412583
Entities
People
- Jacob Wenegrat
Organizations
- Office of Naval Research
- United States Navy
- University of Maryland